Universidad Nacional Mayor de San Marcos, School of Veterinary Medicine, Lima,. Peru. 7. ..... from Isla Noblecilla, and a new resident in Nuevo Progreso.
TAENIA SOLIUM CYSTICERCOSIS HOTSPOTS SURROUNDING TAPEWORM CARRIERS
by Andres G. Lescano, M.H.S., M.H.S.
A dissertation submitted to Johns Hopkins University in conformity with the requirements for the degree of Doctor in Philosophy
Baltimore, Maryland October 2007
2007 Andres G. Lescano All rights reserved
UMI Number: 3309801 Copyright 2007 by Lescano, Andres G.
All rights reserved.
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Dissertation Abstract
Neurocysticercosis, the infection of the central nervous system with the cestode Taenia solium, is a major cause of acquired epilepsy and an important public health problem. This parasite has a two-host life cycle: humans are the definitive host that harbors the adult tapeworm, while both humans and pigs are intermediate hosts and harbor the cysticerci. This dissertation evaluates the clustering of human and porcine cysticercosis surrounding T. solium tapeworm carriers and discusses its implications for epidemiology and control.
This dissertation is presented in three papers. In the first, a short follow-up field study of T. solium cysticercosis and taeniasis, swine seropositivity clustered in hotspots around tapeworm carriers. Swine seroprevalence increased from 18% at >500m from carriers to 69% within 50m, and seroincidence increased from 4% at >500m to 44% within 50m. Pigs owned by carriers had four times more seroincidence than other pigs.
The
second
paper
evaluated
the
aggregation
of
human
cysticercosis
seroprevalence and seizures around carriers. Seroprevalence increased closer to carriers from 21% >50m from carriers to 64% among tapeworm carriers and their families. Seizures, however, were not associated with the distance to the carrier.
Finally, the clustering of necropsy-confirmed viable swine cysticercosis infection around tapeworm carriers was evaluated. Viable infection prevalence formed a
ii
significant gradient going from 0.5% at >500m to 10.6% at 2-500m, and to 70.0% at the carriers' homes. Nearly all pigs with viable infection were within 500m of carriers. The aggregation of viable swine infection and human and swine seropositivity around carriers provides an avenue to apply focused control measures inside transmission hotspots where both infected hosts can be reached. Increased risk was also present among carriers' neighbors and their neighbors' pigs, extending for up to hundreds of meters.
Many gaps remain in our knowledge of cysticercosis' transmission dynamics, such as egg dispersion mechanisms and their implications for disease transmission. With the promise of swine vaccines, the benefits derived of an improved understanding of T. solium epidemiology can be unappreciated. However, the limited impact of control measures call for caution about the success of future interventions until T. solium transmission dynamics are better understood.
Dissertation Readers Lawrence H. Moulton, PhD (Advisor) Robert H. Gilman, MD, DTM&H Kenrad E. Nelson, MD Thaddeus K. Graczyk, MSc, PhD Andrea J. Ruff, MD, MPH Clive J. Shiff, PhD
Acknowledgments To Professor Gilman, mentor and second father, for his unbreakable faith in all of us Peruvians
To my parents, for showing me that hard work was the only way to move forward in life
To Dr. Hector H. Garcia, for opening the door and guiding me into the world of international research
To Dr. Moulton, for his wise advice and patience
To Armando Gonzalez, Victor Tsang and all the other members of the Cysticercosis Working Group in Peru, for their support in preparing this dissertation
To the army of field workers, veterinarians, laboratory scientists, physicians and epidemiologists that contributed with their hard work to conduct this investigation
To Kelika, for bringing a new light into my life
To Talula, for graciously enduring the bumpy rides to Matapalo for nearly three months
To Alfonso, Heidi and Renan, who were at the beginning of this journey in 1989
IV
Dedication
To young researchers in the developing world. There is hope.
To all my friends and relatives who never stopped encouraging me to finish this dissertation, and very specially, to Richard M. Phillips.
v
TABLE OF CONTENTS
Chapter One-INTRODUCTION
1
Chapter Two - BACKGROUND
6
ILL LIFE CYCLE
6
11.2. DIAGNOSIS
9
11.2.1. Diagnostic methods for taeniasis
9
11.2.1.1. Self-report
9
11.2.1.2. Microscopic Examinations
9
11.2.1.3. Examination of Tapeworm Segments
10
11.2.1.4. Coproantigen Detection by ELISA
11
11.2.1.5. Copro-DNA Detection
11
11.2.1.6. Serology
12
11.2.2. Diagnostic methods for human cysticercosis
14
11.2.2.1. Serology
14
11.2.2.2. Neuroimaging
17
11.2.3. Diagnostic methods for swine cysticercosis
20
11.2.3.1. Tongue Examination
20
11.2.3.2. Carcass Evaluation
22
11.2.3.3. Serology
22
11.3. CLINICAL FEATURES
23
II.3.1. Taeniasis
23
vi
11.3.2. Human cysticercosis
24
11.3.2.1. Neurocysticercosis
24
11.3.2.2. Ophthalmic cysticercosis
27
11.3.2.3. Sub-Cutaneous and Muscular cysticercosis .
27
11.3.2.4. Cardiac cysticercosis
27
11.3.3. Swine cysticercosis
29
II.4. TREATMENT
29
11.4.1. Taeniasis
29
11.4.1.1. Praziquantel
30
11.4.1.2. Niclosamide
30
11.4.2. Human Cysticercosis
31
11.4.2.1. Intraparenchymal Cysticercosis
33
11.4.2.2. Subarachnoid Cysticercosis
34
11.4.2.3. Ventricular Cysticercosis
34
11.4.3. Swine Cysticercosis
35
11.4.3.1. Praziquantel and Albendazole
35
11.4.3.2. Oxfendazole
36
H.5. DISEASE BURDEN
38
11.6. EPIDEMIOLOGY
40
11.6.1. Taeniasis
40
11.6.2. Human Cysticercosis
42
11.6.3. Swine Cysticercosis
45
11.7. EGG DISPERSION MECHANISMS
46
vii
II.7.1.Wind
47
11.7.2. Birds
47
11.7.3. Flies
47
11.7.4. Dung beetles
48
II.7.5.Pigs
48
11.8. CLUSTERING AROUND CARRIERS 11.8.1. Taenia solium cysticercosis 11.8.2. Experiments on T. hydatigena and T. ovis 11.9. PREVENTION AND CONTROL 11.9.1. Mass Chemotherapy
49 50 52 56 57
11.9.1.1. China
58
11.9.1.2. Mexico
58
11.9.1.3. Ecuador
59
11.9.1.4. Guatemala
59
II.9.1.5.Peru
59
11.9.2. Education
60
11.9.3. Vaccination
61
Chapter Three - SWINE CYSTICERCOSIS HOTSPOTS SURROUNDING TAENIA SOLIUM TAPEWORM CARRIERS
63
III. 1. ABSTRACT
65
111.2. INTRODUCTION
66
111.3. MATERIAL AND METHODS
68
via
111.3.1. Study Site
68
111.3.2. Study Design
68
111.3.3. Research Ethics
68
111.3.4. Taeniasis Mass Treatment
69
111.3.5. Tapeworm Detection
69
111.3.6. Swine Serosurveys
70
111.3.7. Statistical Analyses
71
111.4. RESULTS
73
111.4.1. Study Population
73
111.4.2. Tapeworm Detection and Treatment
73
111.4.3. Treatment Effectiveness
75
111.4.4. Pig Farming Practices
75
111.4.5. Distance Gradients
76
111.4.6. Risk Factors for Seroprevalence
80
111.4.7. Risk Factors for Seroincidence
82
111.5. DISCUSSION
84
Chapter Four - TAENIA SOLIUM CYSTICERCOSIS HOTSPOTS SURROUNDING TAPEWORM CARRIERS: CLUSTERING ON HUMAN SEROPREVALENCE BUT NOT ON SEIZURES
87
IV.l. ABSTRACT
89
IV.2. INTRODUCTION
90
IV.3. MATERIAL AND METHODS
91
ix
IV.3.1. Study Design and Site
91
IV.3.2. Taeniasis Mass Treatment and Tapeworm Detection .
92
IV.3.3. Human Serosurvey
92
IV.3.4. Neurologic Evaluations
93
IV.3.5. Swine Serosurvey
93
IV.3.6. Statistical Analyses
93
IV.4. RESULTS
95
IV.4.1. Census
95
IV.4.2. Serological and Stool Surveys
96
IV.4.3. Seizure Cases
96
IV.4.4. NCC-Related Seizures
96
IV.4.5. Seroprevalence and Seizure Prevalence Around Carriers
99
IV.4.6. Other Variables Associated with Seroprevalence IV.5. DISCUSSION
102 102
Chapter Five - CLUSTERS OF CONFIRMED SWINE CYSTICERCOSIS INFECTION AROUND TAENIA SOLIUM TAPEWORM CARRIERS
106
V.l. ABSTRACT
108
V.2. INTRODUCTION
109
V.3. MATERIAL AND METHODS
109
V.3.1. Study Site
109
X
V.3.2. Study Design
110
V.3.3. Research Ethics
110
V.3.4. Taeniasis Mass Treatment
110
V.3.5. Tapeworm Detection
Ill
V.3.6. Swine Serology and Necropsy
112
V.3.7. Statistical Analyses
114
V.4. RESULTS
115
V.4.1. Census and Tapeworm Detection
115
V.4.2. PigFarming and Swine Cysticercosis
117
V.4.3. Infection Distance Gradients
121
V.4.4. Seroprevalence Gradients
124
V.5. DISCUSSION
125
Chapter Six - INTEGRATED DISCUSSION
129
VI. 1. Conclusions
129
VI.2. Limitations
134
VI.3. Directions of Future Research
138
VI.3.1. Define the Appropriate Radius of the Intervention Target Zone
138
VI.3.2. Revisit the Intervention Package and its Delivery
138
VI.3.3. Improve Diagnostic Tools for Cysticercosis Infection .
139
VI.3.4. Enhance our Understanding of Transmission Mechanisms
139
XI
REFERENCES
141
CURRICULUM VITAE
160
xii
LIST OF TABLES
Table 1. Revised diagnostic criteria for neurocysticercosis
13
Table 2. Revised degrees of certainty for the diagnosis of neurocysticercosis
15
Table 3. Treatment guidelines for the diverse forms of neurocysticercosis ..
32
Table 4. Cyst counts in grazing lambs before and after introducing a T. hydatigena tapeworm carrier
53
Table 5. Baseline sociodemographics of the human and swine population, prevalence of taeniasis and swine cysticercosis seropositivity, Tumbes, Peru, 1999-2000
74
Table 6. Baseline seroprevalence of swine cysticercosis by selected risk factors, Tumbes, Peru, 1999-2000
79
Table 7. Multiple regression analysis of baseline seroprevalence of swine cysticercosis by selected risk factors, Tumbes, Peru, 1999-2000
82
Table 8. Seroincidence rate of swine cysticercosis by selected risk factors, Tumbes, Peru, 1999-2000
83
Table 9. Seizure frequency by distance to the nearest tapeworm carrier, Tumbes,Peru, 1999
100
Table 10. Covariate associations with the seroprevalence of human cysticercosis, Tumbes, Peru, 1999
101
Table 11. Characteristics of the human and swine population and number of T. solium tapeworm carriers by village, Tumbes, Peru, 2005
xiii
116
Table 12. Necropsy-confirmed T. solium swine cysticercosis infection, Tumbes, Peru, 2005
118
Table 13. Distance to the nearest T. solium carrier and swine cysticercosis risk, Tumbes, Peru, 2005
120
Table 14. Risk factors for the presence of one or more viable T. solium cysts on swine, Tumbes, Peru, 2005
123
XIV
LIST OF FIGURES
Figure 1. Life cycle of Taenia solium
2
Figure 2. Stages of Cysticercosis/Taeniasis
8
Figure 3. Parenchymal neurocysticercosis with three viable cysts
19
Figure 4. Positive visual tongue examination
21
Figure 5. Neurocysticercosis with multiple calcifications and a shunt valve alleviating intracranial hypertension
26
Figure 6. Pig brain massively infected with viable T. solium cysts with noticeable scoleces
28
Figure 7. Ten adult, mature T. solium tapeworms recovered from a single patient after treatment with niclosamide and purge with electrolytepolyethyleneglycol salt
42
Figure 8. Layout of grazing plots
53
Figure 9. Taenia hydatigena and T. ovis cyst counts found in an investigation of an accidental outbreak of cysticercosis Figure 10. Study site and swine population, Tumbes, Peru
55 67
Figure 11. Gradients of swine cysticercosis seroprevalence and four-month cumulative seroincidence by distance to the nearest Taenia solium tapeworm carrier, Tumbes, Peru, 1999-2000
78
Figure 12. Seroprevalence and four-month seroincidence of swine cysticercosis and location of Taenia solium tapeworm carriers, Tumbes,Peru, 1999-2000
81
XV
Figure 13. Proportion seroprevalence of human cysticercosis and location of T. solium tapeworm carriers and NCC-related cases, Tumbes, Peru, 1999
97
Figure 14. Household human cysticercosis seroprevalence (2a) and NCC-related seizure prevalence (2b) by distance to the nearest T. solium tapeworm carrier, Tumbes, Peru, 1999
98
Figure 15. Transportation of pigs to field laboratory and necropsy procedures, Tumbes, Peru 2005
113
Figure 16. Location of pig farms and Taenia solium tapeworm carriers, Tumbes, Peru, 2005
119
Figure 17. Swine cysticercosis infection and seroprevalence gradients by distance ranges, Tumbes, Peru, 2005
XVI
122
Chapter One INTRODUCTION
Neurocysticercosis (NCC), the infection of the central nervous system with the cestode Taenia solium, affects approximately 50 million people worldwide and is considered the single major cause of acquired epilepsy in the world[l-4] and thus an important public health problem. This zoonotic parasite has a complex two-host life cycle. Humans are the only definitive host and harbor the adult tapeworm, and both humans and pigs may act as intermediate hosts and harbor the larvae or cysticerci (Figure 1). Neurocysticercosis is highly endemic in different parts of the developing world where pigs are raised for food and sanitation infrastructure is limited. [5, 6] The disease is endemic throughout Latin America, and in most countries in Asia, Sub-Saharan Africa and Oceania. Recently, neurocysticercosis has also become increasingly diagnosed in industrialized countries as a result of immigration of tapeworm carriers. [6-9]
Taeniasis, the infection with the adult stage of the parasite, is acquired by the ingestion of raw or improperly cooked pork infected with T. solium cysts. When ingested, cysts enter the digestive system and evaginate in the small intestine, attaching to the intestinal mucosa. The adult tapeworm forms within approximately two months, but causes little if any disability or morbidity. [10] The most distal proglottids detach periodically and disseminate mature eggs in the environment with the stools of tapeworm carriers, which can occasionally reach either pigs or humans.
1
Figure 1. Life cycle of Taenia solium. From Garcia and Martinez, Eds., Taenia Solium Taeniasis/Cysticercosis. Permission requested from authors. Human (Definitive host) Ingestion of infected pork, poorly cooked: Tacnio*u 1 ngestton of T. solium eggs by fecal contamination: Human cysfkexcoeis
Ingestion of T, sotiutn eggs or proglottids: Porcine cysticercosis
Kg (Interme diate host)
Swine, the intermediate host, are infected with T. solium eggs by direct ingestion of human feces, although exposure through contaminated water, soil, vegetables or insects is also possible. Humans, on the other hand, are infected mostly by accidental ingestion of Taenia eggs by fecal oral infection. In both humans and pigs, the embryos contained in the eggs cross the intestinal mucosa, are transported by the circulatory system, and then are distributed throughout the body. Cysts most often establish in muscle, eyes and brain, causing cysticercosis. Clinical manifestations reflect the
2
compromise of the affected organs. Swine cysticercosis mostly involves infection in muscle, brain and tongue. In humans, cysticercosis outside the nervous system is mostly asymptomatic and cysts are often destroyed by the host's immune response. Symptoms usually result from parasites located in the eye or the central nervous system, causing neurocysticercosis (NCC). Clinical manifestations of NCC are varied and non-specific, related to individual differences in the number, size, location and stage of lesions and in the severity of the host's immune response to the parasites. [11, 12]
Both taeniasis and cysticercosis cluster within households. Allan et al. demonstrated an unusually high rate of multiple tapeworm carriers in a single household was found in Guatemala. [13] Garcia et al. demonstrated evidence of household clustering of human cysticercosis defined by seroprevalence.[14] Clustering of swine cysticercosis has not been formally demonstrated, but it is reasonable to expect that several pigs in a herd would acquire infection together due to common risk factors and shared exposures. Other clustering patterns, however, such as aggregation surrounding tapeworm carriers, are likely to occur but have not been rigorously studied for T. solium cysticercosis. Common understanding of the life cycle shows that both tapeworm carriers and their contacts have increased cysticercosis seroprevalence rates compared to individuals without close contact to carriers.[14] However, is not well known if tapeworm carriers can contaminate the environment beyond their immediate surroundings, or how far from a carrier the risk of acquiring cysticercosis remains significantly increased. Similarly, it is conceivable that pigs owned by a tapeworm carrier could have higher cysticercosis rates compared to other pigs, but surprisingly none of these hypotheses have been evaluated to
3
date. Evidence from experimental studies about the transmission of T. hydatigena and T. ovis demonstrated that there is higher risk of cysticercosis nearer canine carriers, and a gradient of increased risk is observed progressively closer to carriers.[15, 16] Sheep, however, are coprophobic[17] and their cestodes require the dissemination of eggs in pasture. Pigs, on the other hand, are coprophagic,[18, 19] and for that reason the broad spread of infection observed in T. hydatigena and T. ovis transmission may not occur in T. solium cysticercosis.
It has been suggested that control programs for T. solium cysticercosis should include a cost-effective, practical combination of interventions targeting both the intermediate and definitive hosts of the disease, pigs and humans, respectively [10]. Mass combined interventions, however, imply an inherent logistical burden and may be difficult to implement and sustain over time. Clustering of cysticercosis infection around carriers, if present, would provide a narrow target area where control interventions could be focused efficiently. Focused interventions will probably use less resources than massive campaigns to reach both tapeworm carriers humans and cysticercotic pigs. The strength of the clustering and the size of the transmission hotspots surrounding carriers would influence the efficiency of this approach.
This dissertation evaluates the presence, magnitude and geographical extent of clustering of swine and human cysticercosis surrounding tapeworm carriers in order to provide evidence that could guide control interventions in the future. The document is divided in three related manuscripts. The first paper is entitled "Swine cysticercosis
4
hotspots surrounding Taenia solium tapeworm carriers", and evaluates clustering in swine cysticercosis seroprevalence and seroincidence, key parameters to assess the risk of further disease transmission. The second paper is entitled "Taenia solium cysticercosis hotspots surrounding tapeworm carriers: clustering on human seroprevalence but not on seizures", and evaluates if patterns of swine seropositivity are also present for human cysticercosis seroprevalence and neurocysticercosis-related seizure cases. Finally, the third paper is entitled "Clusters of confirmed swine cysticercosis infection surrounding Taenia solium tapeworm carriers", and uses necropsy-confirmed viable swine infection, the gold standard measure of disease burden, to evaluate the presence of hotspots of viable infection surrounding carriers, as well as their size and magnitude. Together, the three papers provide a comprehensive overview of the clustering patterns of different markers of exposure and infection in both humans and pigs and illustrate the value and possible interpretation of the resulting epidemiological parameters.
5
Chapter Two BACKGROUND
II.l LIFE CYCLE Taenia solium is a zoonotic cestode of the genus Taenia and has a complex twohost life cycle. Humans are the only definitive host of the adult tapeworm; both humans and pigs can act as intermediate hosts, harboring the larvae or cysticerci (Figure 1). The adult tapeworm has three main components, a scolex with four suckers and a rostellum or double crown of hooks, a narrow neck, and a strobila formed by several hundred of proglottids that usually measures 2 to 4 meters but can exceptionally reach 10 meters. The more distal proglottids of mature tapeworms are usually gravid, and are frequently detached from the worm and expelled with feces, disseminating 50,000 to 60,000 eggs per proglottid. Taeniasis, the infection with the tapeworm or adult stage of the parasite (Figure 2) occurs only in the human host and is acquired by the ingestion of raw or poorly cooked pork infected with T. solium cysts. The experiments of Kuchenmaister (1855) confirmed the link between taeniasis and cysticercosis, and showed that young tapeworms could be detected in necropsy from prisoners who were fed infected pork. [20] Viable T. solium cysts present in pork evaginates in the small intestine after ingestion, and the scolex attaches strongly to the intestinal mucosa by the suckers and hooks. Then the parasite starts forming segments or proglottids and after 2-3 months reaches adult form, [21] although causing little if any morbidity to the host. [10] At that time, proglottids mature
6
and the most distal segments begin detaching from the rest of the worm spreading fertile T. solium eggs in the environment, which can reach either pigs or humans. Cysticercosis is the infection with the larval stage of the parasite T. solium following the ingestion of viable eggs. Swine, the intermediate host, are often infected with T. solium eggs by direct ingestion of human feces, although exposure through contaminated water, soil, vegetables or insects is also possible. Humans are infected primarily by accidental ingestion of Taenia eggs by fecal oral infection. After ingestion, gastric acid helps to liberate the embryos or oncospheres contained in the eggs, which cross the intestinal mucosa and are then transported by the circulatory system to the liver and lungs. It appears that a proportion of all embryos are cleared in the liver[22] and the rest of the surviving parasites reach skeletal muscle, the brain or other tissue and in approximately three months develop into larval vesicles also called cysts or cysticerci.[23] Cysts are most often found in muscle, eyes and brain (Figure 2), and they can cause diverse clinical manifestations in humans depending on their number, stage, location and immune reaction of the host. Seizures are one of its most apparent symptoms, and tend to appear 3-5 years after exposure generally after the degeneration and death of cysts.[4] Swine cysticercosis, however, rarely presents with clinical symptoms not even for massive infections. Pigs are often slaughtered on average at 9-12 months of age [24] and this is most likely before cysts have had enough time to deteriorate and die.
7
Figure 2. Stages of Cysticercosis/Taeniasis Photos courtesy of Javier Bustos, Hector Garcia and Guillermo Gonzalvez
..M
Adult T. solium specimen under the microscope
Pork infected with high parasitic burden
Multiple viable T. solium cysts found in a single pig. Scoleces are clearly recognizable
8
II.2. DIAGNOSIS
II.2.1. Diagnostic methods for taeniasis. A number of alternatives exist to assess the presence of the adult form of the cestode, and most of them depend on the detection of parasite material in stools. Several of the existing methods, however, are limited by the unreliable excretion of parasite material in feces and the morphological similarity of the human tapeworms, T. solium, T. saginata and T. saginata asiatica.
11.2.1.1.
SELF-REPORT.
The expulsion of proglottids in T. solium taeniasis is
passive and rarely noticeable by carriers.[13, 21] In contrast, the proglottids of T. saginata are more motile and actively come out of the carrier's anus, and are often found in the clothes of the carrier[25, 26]. Self-report and questioning about a history of passing tapeworm segments has very low sensitivity and specificity[27] and is used in epidemiological studies mostly as a risk marker but rarely as method of diagnosis.[27] Additionally, questioning and self-report often have a poor positive predictive value because subjects may confuse tapeworm segments with nematodes[21, 28] and tapeworm infections may be interrupted by treatment or natural death of the parasite soon after passage of proglottids.
11.2.1.2. MICROSCOPIC
EXAMINATIONS.
Classic parasitological examinations are
known to have poor sensitivity to diagnose taeniasis. Direct visualization of Taenia eggs was one of the first diagnostic methods used, but missed approximately 60%-70% of all cases,[13] most likely limited by the intermittent
9
nature of egg excretion. [29] The sensitivity of the test can be improved by using repeated serial stool specimens.[30, 31] The Graham "scotch tape" test has also been used with limited sensitivity for T. solium although better results for T. saginata. [27, 29, 32]. The test is implemented applying adhesive tape to the perianal region, and using the tape to swab the area. The presence of eggs is determined then by microscopic examination of the tape.[25] However, none of these is able to differentiate the infecting species because the eggs of T. solium, T. saginata and T. asiatica are morphologically indistinguishable.
II.2.1.3.
EXAMINATION O F TAPEWORM SEGMENTS.
Species differentiation can
be performed by macroscopically identifying the unique features of the scoleces and segments of each human tapeworm species. Identification of T. solium, for example, can be based on three morphological features of mature, gravid proglottids: 1) the presence of three ovarian lobes, 2) The absence of a vaginal sphincter, and 3) the presence of 7-11 unilateral uterine branches.[33] Morphological assessments can be facilitated by longitudinal sectioning of the gravid proglottid followed by haematoxylin-eosin staining.[34] If the scolex is recovered, the characteristic presence of the double crown of hooks would identify the species as T. solium.[27] The methods described above, however, are limited by a number of factors. Modern cysticidal drugs cause the disintegration of the proximal end of the worm and therefore reduce the chances of recovering the scolex after treatment. [24] Even with the use of a purge immediately before treatment, scoleces and
10
proglottids have only been recovered in 25% and 53% of all carriers, respectively.[35]
Morphological
diagnosis
using
proglottid
materials,
additionally, is not absolute due to the occurrence of some overlap in the number of uterine branches between species[36] as well as morphological abnormalities.
11.2.1.4.
COPROANTIGEN DETECTION BY
ELISA. In 1990, Allan et al. reported
an enzyme-linked immunoabsorvent assay (ELISA) test to detect parasite-specific molecules (copro-antigens) in the feces of tapeworm carriers, thus demonstrating current infection with an adult tapeworm. This assay has 95% sensitivity and specificity greater than 99%, detecting 2.6 times as many cases as traditional stool microscopy assessments and immediately becoming an effective tool for epidemiological studies and individual diagnoses.[13, 37-39] Additionally, this assay can detect the presence of a tapeworm before egg production began, and ceases to detect it within a week after treatment. [3 7] Although the coproantigen ELISA assay has no cross-reactions with other intestinal helminth infections, a major disadvantage is that it cannot differentiate T. solium and T. saginata infections.[37] The coproantigen ELISA has also been implemented in a dipstick format, although its sensitivity was only 76%. [40, 41]
11.2.1.5.
C O P R O - D N A DETECTION.
Several molecular approaches have been
developed to detect the presence of T. solium DNA in human feces, mainly with the purpose of discriminating T. solium and T. saginata infections.[34, 39, 42-45] Several highly sensitive methods based on polymerase chain reaction (PCR) exist,
11
and most of them can amplify small amounts of oncospheric DNA, although they require sophisticated equipment and facilities unavailable in most settings where cysticercosis is endemic.
II.2.1.5.
SEROLOGY.
The diagnoses of T. solium taeniasis by the detection of
circulating antibodies using an immunoblot assay (EITB) was recently demonstrated by Wilkins et al.[46] This assay has 95% sensitivity and did not present cross-reactions on subjects with other parasitic diseases such as Echinococcus, Hymenolepis nana, Ascaris, filariasis and schistosomiasis. Its specificity, however, appears to be impaired by the detection of remaining antibodies long after removal of the intestinal parasite.[47] Also, the production of T. solium excretory secretory products is expensive, time-consuming and labor intensive. A new assay based on recombinant forms of the proteins TSES33 and TSES38 was successfully developed,[48] and recently demonstrated 97% sensitivity and 100% specificity using the rES33 antigen.[49]
12
Table 1. Revised diagnostic criteria for neurocysticercosis, as reported by Del Brutto OH et al. Proposed diagnostic criteria for neurocysticercosis. Neurology. 2001 Jul 24;57(2): 177-83 Categories of Criteria criteria Absolute 1. Histologic demonstration of the parasite from biopsy of a brain or spinal cord lesion 2. Cystic lesions showing the scolex on CT or MRI 3. Direct visualization of subretinal parasites by fundoscopic examination Major 1. Lesions highly suggestive of neurocysticercosis on neuroimaging studies* 2. Positive serum EITBf for the detection of anticysticercal antibodies 3. Resolution of intracranial cystic lesions after therapy with albendazole or praziquantel 4. Spontaneous resolution of small single enhancing lesionsj Minor 1. Lesions compatible with neurocysticercosis on neuroimaging studies § 2. Clinical manifestations suggestive of neurocysticercosis!! 3. Positive CSF ELISA for detection of anticysticercal antibodies or cysticercal antigens 4. Cysticercosis outside the CNS^f Epidemiologic 1. Evidence of a household contact with Taenia solium infection 2. Individuals coming from or living in an area where cysticercosis is endemic 3. History of frequent travel to disease endemic areas * CT or MRI showing cystic lesions without scolex, enhancing lesions, or typical parenchymal brain calcifications | Enzyme-linked immunoelectrotransfer blot assay using purified extracts of Taenia solium antigens, as developed by the Centers for Disease Control and Prevention (Atlanta, GA) % Solitary ring-enhancing lesions measuring less than 20 mm in diameter in patients presenting with seizures, a normal neurological examination and no evidence of an active systemic disease § CT or MRI showing hydrocephalus or abnormal enhancement of the leptomeninges, and myelograms showing multiple filling defects in the column of contrast medium I! Seizures, focal neurologic sign, intracranial hypertension, and dementia ^f Histologically confirmed subcutaneous or muscular cysticercosis, plain X-ray films showing "cigar-shaped" soft-tissue calcifications, or direct visualization of cysticerci in the anterior chamber of the eye
13
II.2.2. Diagnostic methods for human cysticercosis. It has been clearly established that the clinical presentation of human cysticercosis depends on the number, location, size, and stage or viability of cysts, as well as the presence of inflammation.[50] Considering all the possible combinations of these factors, it is not surprising that cysticercosis can present with virtually all possible neurological symptoms[51], complicating the diagnosis of the disease. Recognizing this heterogeneity, standardized diagnostic criteria for human cysticercosis were first proposed in 1996[52] and later refined specifically for neurocysticercosis in 2001 after an expert meeting in Lima, Peru.[53] Both the criteria proposed in 1996 and 2001 are based primarily on a combination of imaging and serological evidence combined with clinical and epidemiological findings. Table 1 presents the categories and specific criteria proposed, and Table 2 shows the proposed 'degrees of certainty' for each combination of criteria. The following sections provide additional detail about the different
tools used for the diagnosis of human
neurocysticercosis. II.2.2.1.
SEROLOGY.
The availability of immunodiagnosis tests for the diagnosis
of T. solium cysticercosis by serology provided an excellent tool to understand the epidemiology of cysticercosis and support the diagnosis and management of clinical cases. However, since the physician needs to know the number, location, size and stage of the parasites on the brain to make therapeutic choices, serology for human cysticercosis is mostly used as a screening tool and for confirmatory purposes in conjunction with brain imaging. Different approaches for antibody and antigen detection exist, with varied sensitivity and specificity, as well as interpretation.
14
Table 2. Revised degrees of certainty for the diagnosis of neurocysticercosis. As reported by Del Brutto OH et al. Proposed diagnostic criteria for neurocysticercosis. Neurology. 2001 Jul 24;57(2): 177-83 Diagnostic Criteria certainty Definitive 1. Presence of one absolute criterion 2. Presence of two major plus one minor and one epidemiologic criterion Probable 1. Presence of one major plus two minor criteria 2. Presence of one major plus one minor and one epidemiologic criterion 3. Presence of three minor plus one epidemiologic criterion The presence of two different lesions highly suggestive of neurocysticercosis on neuroimaging studies should be considered as two major diagnostic criteria. However, positive results in two separate types of antibody detection tests should be interpreted only on the bases of the test failing in the highest category of diagnostic criteria.
Antibody detection by EITB. Different techniques are available to detect antibodies to T. solium, including both enzyme-linked immunoabsorvent assay (ELISA) as well as enzyme-linked immunoelectrotransfer blot (EITB). The test of choice is the EITB developed at the Centers for Disease Control and Prevention,[54, 55] an immunoblot of seven glycoproteins purified by lentil-lectin chromatography. This test is 98% sensitive for infection with two or more cysts and 100% specific, but is less sensitive in patients with calcified lesions only, and can be as low as 28% in cases with only a single cyst in the brain.[56] Careful interpretation of EITB results is required in clinical and epidemiological settings, because the presence of antibodies only indicates exposure to infection and not always actual disease. Also, it has been demonstrated that antibody response can be short lived, with up to 40% seroreversion of EITB positive during only a year. [57] Finally, EITB has limited value for post-treatment follow-up of
15
confirmed neurocysticercosis patients because antibodies may persist for a long time after parasite elimination. [5 8] Despite these limitations, EITB is regularly used as confirmatory test to neuroimaging assessments.[53] Additionally, it has been extremely valuable for conducting epidemiological studies to identify risk factors associated with the transmission of T. solium cysticercosis, and to identify communities with increased seroprevalence where control measures are needed.[59, 60] Antibody detection by ELISA. Antibody-detecting ELISA tests provide a simpler and more affordable assay for developing country settings, although its sensitivity and specificity traditionally has been lower than EITB's.[61, 62] Additionally, the test has been plagued by cross-reactions with other cestode infections.[62-64] It has been suggested that ELISA test should be used mainly with cerebrospinal fluid (CSF),[27] although the invasiveness of this approach clearly limits its use. Recently, however, improvements in the purification of glycoproteins from cyst fluid have led to the development of an antibody-ELISA, reportedly with 90% sensitivity and 100% specificity,[65] and without cross-reactions with T. hydatigena.[66] Antigen detection by ELISA. Antigen detection assays can detect live parasites and present a suitable alternative to antibody detection for monitoring antiparasitic therapy, [27, 67] although only limited evidence exists about its sensitivity and specificity. Garcia et al. reported 85% sensitivity of a serum antigen-detecting ELISA in EITB+ patients, the highest reported yet, although the sensitivity decreased to 65%) in patients with a single viable cyst or enhancing lesions
16
only.[68] Monoclonal antibodies, particularly in CSF, appear to perform better, [68-70] although lumbar punctures are clearly more invasive and burdensome. [67]
II.2.2.2.
NEUROIMAGING.
The diagnosis of neurocysticercosis was greatly
improved with the advent of neuroimaging techniques, specifically allowing a better description of the number, location and size of lesions in the brain, as well as the presence and degree of inflammatory reactions. [71] Positive brain imaging is one the three absolute criteria for the diagnosis of neurocysticercosis,[53] although in most cases imaging findings are not always pathognomonic and often need to be confirmed with serological tests.[72] The degenerative stages of cysticerci are classified in four stages: viable, colloidal, nodular-granular and calcified. [73] Viable, healthy T. solium cysticerci are seen on neuroimaging as hypodense images with an eccentric hyperdense nodule representing the scolex, a pathognomonic feature called "hole-with-dot". Colloidal cysts appear surrounded by edema resulting from the reaction of the host immune system, usually visible after contrast administration. Nodulargranular lesions are hyperdense images surrounded visualized with edema after contrast (granulomas), called single enhancing lesions if only one is present. [74] Calcifications of dead cysts show as small, punctate hyperdense lesions. Multiple lesions are not uncommon, often with cysts in different stages, and neuroimages resemble the appearance of Swiss cheese.
17
Computed tomography (CT). Initial evidence of the value of computed tomography for the diagnosis of neurocysticercosis was published in 1977,[75, 76] and provided substantial advantages over existing methods. Computer tomography is non-invasive, well tolerated and has minimum exposure to X-rays. Additionally, CT is cheaper and more available than magnetic resonance in endemic settings, therefore remaining the most widely available screening neuroimaging procedure. The use of CT allowed the description of the evolution of the parasite in the brain and the classification of the different presentations of the disease, providing the basis to propose therapeutic approaches specific for each presentation[77, 78]. The sensitivity and specificity of CT reportedly exceeds 95% for most forms of neurocysticercosis, although its sensitivity is lower for some presentations of the disease such as ventricular or cisternal neurocysticercosis. For ventricular cysticercosis with obstructive hydrocephalus, for example, only indirect evidence can be seen on CT such as cavity enhancement/deformation. As a result, more often than not, CT imaging results are not pathognomonic of neurocysticercosis. [79] For calcified cysts, however, CT is more sensitive than magnetic resonance,[80, 81] as this type of lesions usually cannot be visualized on MRI.[71]
18
Figure 3. Parenchymal neurocysticercosis with three viable cysts. MRI using FLAIR technique at baseline and after 6 months of treatment with Albendazole at 15 mg/kg day for two weeks. Photo courtesy of Javier Bustos and Javier Pretell
P.ESJUHSA -
E1 month, with high doses of steroids; or surgical excision Albendazole 15 mg/kg/day for >1 month, with high doses of steroids Endoscopic aspiration or surgical resection, use of antiparasitic drugs is controversial No antiparasitic treatment, ventricular shunt No antiparasitic treatment, high doses of steroids for >1 month No antiparasitic treatment, ventricular shunt if indicated, high doses of steroids
Surgical resection, albendazole may be used Surgical resection
32
Garcia et al.[50] highlighted four key issues in neurocysticercosis management: 1) handling seizures, headache and inflammation, 2) dealing carefully with intracranial hypertension, if present, 3) paying special attention to presentations at high-risk of complications and death, and 4) individualizing treatment according to cyst location, inflammation and clinical features. Neurologists' attention to these crucial points, however, has been continuously distracted by the ongoing debate regarding the benefits of using anti-parasitic drugs. [132] The diversity of presentations of the disease, lack of controlled trials for therapeutic approaches, and limited understanding of the pathophysiologic processes that determine clinical illness further complicate the clinicians' responsibilities. Existing treatment guidelines acknowledge the existence of these limitations, and propose relevant questions to respond in the future.[133] A simplified overview of the most general approaches proposed is listed in Table 3 and is briefly presented in the following sections. H.4.2.1.
INTRAPARENCHYMAL CYSTICERCOSIS.
A recent placebo-controlled trial
of the treatment of viable intraparenchymal cysts with albendazole demonstrated a long-term benefit of anti-helmintic therapy in reducing generalized seizures compared to placebo. [134] The results of this study were confirmed in 2006 by a meta-analysis
of
anti-helmintic
treatment
studies
for
parenchymal
cysticercosis.[135] Alternatively, praziquantel can be used in a single- or 15-day dosage.[100, 136] The results of the meta-analysis also apply to the treatment of single enhancing lesions, suggesting a benefit from antiparasitic treatment. [133, 135] There is no reason, on the other hand, to use antiparasitic drugs to treat calcified cysticerci.[50] In patients with massive infection and cysticercotic
33
encephalitis, antiparasitic drugs may increase intracranial hypertension and should not be used. [78] 11.4.2.2.
SUBARACHNOID CYSTICERCOSIS.
Handling intracranial hypertension is
the main priority for cases of subarachnoid or sylvian cysticercosis.[50] Although there are no controlled trials, recent case series using anticysticidals with steroids and shunts have shown better results than previous series,[112, 137, 138] and most experts consider than anti-helmintic drugs are warranted.[78] Antiparasitic treatment is needed to stop the growth of the cysts, but in patients with hydrocephalus this should be done only after placing a ventricular shunt to handle the additional intracranial hypertension resulting from administering anticysticidal drugs.[50] Treatment with steroids is mandatory in most cases to prevent stroke. 11.4.2.3.
VENTRICULAR CYSTICERCOSIS.
Cysticerci lodged in the ventricles may
cause hydrocephalus by blocking CSF flow or via inflammation, often requiring the placement of ventricular shunts. Albendazole can treat most ventricular cysts but
may
also
launch
an
acute
inflammatory
reaction
leading
to
hydrocephalus. [114] Therefore, anticysticidals should be administered under a personalized approach. [107] Recent reports suggest that neuroendoscopy conducted by expert hands may be a safer and potentially effective treatment approach.[139-141]
34
II.4.3. Swine cysticercosis. Swine treatment has two equally important goals: 1) interrupt potential disease transmission to the definitive human host and 2) recover the economic market value of infected animals. In order to sell the pigs at average markets prices, treated animals need to be cyst-free and additionally their meat should be free of traces or resemblance of previous infection. II.4.3.1.
PRAZIQUANTEL AND ALBENDAZOLE.
Flisser et al. reported partial effect
of praziquantel treatment for swine cysticercosis,[142] and later a single-dose treatment scheme resulted in 59% effectiveness.[143] Kaur reported 100% efficacy of 30-day treatment with albendazole at 15 mg/kg body weight.[144] However, albendazole treatment apparently caused side effects, as demonstrated in a randomized trial in Peru of two dosages of albendazole compared to placebo. Pigs receiving three-day treatment with a 30 mg/kg body weight dose presented side effects including lethargy and anorexia compared to no side effects in the placebo arm. In the second albendazole arm, all seven pigs receiving a single dose of 50 mg/kg presented side effects including extreme prostration, complete anorexia and reluctance to move, and one animal died. Treatment effectiveness measured by necropsy at 12 weeks post treatment was 100% with a three-day dose and 88-93% effective with a single dose, although both albendazole arms left dead and degenerated cysts. On necropsy the meat looked measly and unsuitable for being sold in markets.[145] Another treatment strategy was tested in Mexico using an 8-day two-injection scheme using albendazole sulphoxide at 15 kg/mg. This approach also reached 100% efficacy killing cysts in muscle 12 weeks post-
treatment, but treatment was apparently unable to achieve a complete visual disappearance of cysts in muscle. [146] II.4.3.2.
OXFENDAZOLE.
Gonzalez et al. conducted four placebo-controlled
randomized trials to evaluate the effectiveness, dosage, and timeliness of effect of oxfendazole for the treatment of swine cysticercosis.[124, 147-149] These trials studied naturally infected pigs and evaluated effectiveness by a detail necropsy procedure applied to muscle, tongue, heart and brain, and included evaluation of the viability of cysts by evagination procedures. The first study demonstrated that a single 30 mg/kg body weight dose of oxfendazole was 100% effective to clear all cysts after 12 weeks post-treatment without any detectable side effects. The meat of the treated animals appeared clean on the naked eye and only minute scars were observed. Pork appeared completely normal and suitable for marketing, without differences in its taste when compared to meat acquired from supermarkets in Lima. [124] The second trial compared the effectiveness of three oxfendazole doses, 10, 20 and 30 mg/kg. In the groups treated with 10 and 20 mg/kg doses, four of six pigs presented cysts in the muscle and brain. Pigs in the 30 mg/kg trial arm achieved 100% treatment efficacy again without side effects, and the carcasses appeared normal on visual inspection, looking suitable for sale.[147] The third trial evaluated the evolution in the effectiveness of 30 mg/kg treatment at 1, 2, 4 and 12 weeks post-treatment to assess how fast the drug acted. Results after one week demonstrated decreased cyst counts and lower viability, but viable cysts were found in all tissues even four weeks after treatment. At 12 weeks post-treatment
36
no pig had live cysts, except for one animal with brain cysts. This study demonstrated that cyst death was not immediate and oxfendazole treatment could not be applied immediately before slaughtering. Another result of this study is that cyst survival in the brain was possible, potentially because of protection from the blood-brain barrier or immune evasion.[150] This finding, however, most likely does not have implications for transmission because pig brain is rarely eaten raw. [27] In a final experiment, Gonzalez evaluated the ability of oxfendazole to protect treated animals against re-infection. Naturally infected, treated pigs were placed in their endemic settings of origin and then matched with naive pigs acquired in a cysticercosis-free commercial farm. All pigs were necropsied after 12 weeks, observing infection in 38% of non-treated pigs versus 0% in treated animals, confirming that oxfendazole protected treated pigs from further infection for at least three months post-treatment. [149] These studies confirmed the safety and efficacy of oxfendazole. This inexpensive veterinary benzimidazole can provide treatment in a single dose, without side effects or visual evidence of previous infection in meat. Although some authors have concerns about the safety of meat of treated pigs for human consumption, [10] the withdrawal time in sheep and cattle is actually short (10 days for a 6 mg/kg dose) and should be lower in monogastric animals like pigs.
37
II.5. DISEASE BURDEN Neurocysticercosis is considered the most common parasitic infection of the central nervous system, and because of its prevalence and substantial burden it has been suggested that it should be declared an international reportable disease.[151] WHO estimates that there are more than 50,000 annual deaths due to human neurocysticercosis, although these figures represent only the tip of a much larger iceberg[72] composed of an estimated 50 million human cases worldwide. While the disease was eliminated from the developed world due to improvements in public sanitation and pig farming practices, cysticercosis remains common in most developing countries where pigs are raised in close contact with humans. In Latin America alone there are approximately 400,000 people living with symptomatic cysticercosis out of an approximately 75 million people living in endemic areas.[152] Cysticercosis is also endemic in most countries in Asia, Africa and Oceania. [10] Migration and tourism have extended the risk to developed countries, and the number of imported and even local cases is increasing due to tapeworm carriers visiting from endemic regions.[33] Cysticercosis is a common neurological diagnosis in hospitals that serve large Hispanic populations in the United States.[153, 154] Cases of cysticercosis are also being diagnosed more frequently in other developed regions of the world.[155-159] Even populations that do not eat pork due to cultural or religious reasons have been shown to be at risk, as demonstrated by cases among Orthodox Jews in New York,[8, 160] Muslims in Kuwait and Saudi Arabia,[161, 162] and vegetarians in India.[163] Neurocysticercosis imposes a heavy burden on affected individuals. Seizures can occur in up to 70% of all cysticercosis patients[2, 108] and are the most debilitating
38
manifestation of the disease. Epileptic patients suffer from the social, psychological and economic impact of the disease, and their quality of life is reduced proportionally to their frequency of seizures.[164] They are stigmatized and suffer from fear and rejection from spouses, relatives and neighbors. In some rural settings where the disease is common, seizures are attributed a magical origin and epileptic patients are thought to be possessed, further increasing the stigma associated with the disease. In these settings, communities tend to outcast and isolate epileptic patients due to fear of contagion or spread of disease, as observed by Avode et al. in Benin.[165] Stigma and disability lead to lower economic productivity,[166] decreasing down to 30% among epileptic patients.[167] Preux reported that 39% of cases were unable to enter the labor marked in Cameroon,[168] while Rajkotia observed in Peru that 66% of cysticercosis patients lost their jobs after disease onset and 61% failed to re-enter the labor market. [169] The disability resulting from the disease has not been assessed to date, but it is most likely sizeable as most patients cannot afford treatment and live with symptoms up to several years or are forced to delay the beginning of treatment. [169] In the developed world, the costs of neurocysticercosis treatment are significant. Hospitalization expenses alone cost an average of $6539 in the United States, while income lost amounts to $1416 per case. [170] These figures are comparable to the overall costs of all medical services required for epilepsy patients.[171] In developing country settings, only a small fraction of patients with neurocysticercosis have access to healthcare and are able to afford treatment. [172] In Peru, these patients spend 54% of an annual minimum wage in the management of the disease during the first year of treatment and 16% during the second year. [169] The costs to the healthcare system are also
39
sizeable, and Roberts estimated that treatment costs in Brazil were 85 million dollars in 1994, [170] while a study in Mexico demonstrated that in 1986 a total of 15 million dollars were spent in the treatment of newly hospitalized patients. [173] Swine cysticercosis causes substantial economic losses to the pig farming industry[174] and imposes a disproportionate burden to small farmers in rural areas [10]. Cysticercosis-infected pigs cannot be sold in formal slaughterhouses were they would be confiscated, so positive animals are often sold in informal markets at 50% of the regular market price or less.[175] In 1980, the annual porcine farming losses in Mexico due to the elimination of infected meat were approximately 43 million dollars[173], accounting for approximately half of the national swine production[176]. In South Africa, a study in 2006 estimated a loss of 5 million dollars only in the East Cape Province, [177] and a conservative estimate of the annual losses in ten African countries was 34 million dollars. [172]
II.6. EPIDEMIOLOGY
II.6.1. Taeniasis. T. solium taeniasis results from the ingestion of raw or poorly cooked pork, and exposure/infection takes place almost exclusively in endemic settings with ineffective meat inspection procedures. Prevalence is fairly low even in highly endemic settings, ranging from 0.3% to 6.0%,[178, 179] although these figures may be underestimated due to the low sensitivity of microscopic diagnosis [3 7] and the erratic nature of egg excretion[31]. Incidence estimates are very rare, a study in Guatemala suggested 0.8% incidence (7/851) over 10 months.[180]
40
Allan's work in Guatemala confirmed the clustering of T. solium tapeworm carriers within households,[13] a finding observed in multiple other field studies.[89, 181-184] Clustering of tapeworm carriers may be related to common exposure opportunities, whether simultaneous or at different times. For instance, Diaz-Camacho reported in a carefully described study that five of the six T. solium tapeworm carriers detected lived in four neighboring households. Exposure to raw meat was probably direct, as the local butcher lived in one of these households, and his family was related to the other three neighboring households.[181] Prevalence has been observed to be 50% higher in females compared to males[13, 59, 183] and higher rates have been observed in subjects 5 - 3 9 years old.[13] The low numbers of tapeworm carriers detected in epidemiological studies limits the assessment of risk factors for taeniasis. Only one study reported higher rates of taeniasis associated with living in a household that owns infected pigs and eating infected pork.[185] As confirmed detection of a tapeworm is uncommon, a history of passing tapeworm segments is often studied instead despite its poor sensitivity and specificity to identify current tapeworm carriers. [90] Factors found associated to reported passage of tapeworm segments were reporting eating uncooked pork (prevalence ratio=4.5),[186] having owned infected pigs (OR=2.6) and having eaten infected pork (OR=1.9).[187] Traditional understanding of taeniasis suggested that carriers harbored only one T. solium tapeworm, although there were isolated reports of multi-infestation.[13, 131] Improved recovery of tapeworm segments after anti-helmintic therapy, however, showed multiple tapeworms in four out of 20 subjects who expelled scoleces after treatment, demonstrating that T. solium taeniasis is not necessarily solitaire (Figure 7).[35]
41
Figure 7. Ten adult, mature T. solium tapeworms recovered from a single patient after treatment with niclosamide and purge with electrolyte-polyethyleneglycol salt
Photo courtesy qf Javier Bustos
42
II.6.2. Human cysticercosis. Human cysticercosis arises from accidental ingestion of T. solium eggs through fecal-oral contamination. Most infection takes place in endemic settings, but transmission can also occur in non-endemic settings.[8, 160] Non-accidental infection can occur, according to Willingham, who reported that unqualified, self-taught healers in South Africa occasionally use pulverized Taenia segments to treat taeniasis.[10] Furthermore, Kriel reported the malevolent practice of adding T. solium segments to beverages as punishment to unfaithful wives or spouses.[188] These practices, however, appear to be fairly uncommon. The knowledge about the epidemiology of human infection with T. solium cysts improved substantially with the advent of brain imaging. [27] However, only two comparative studies of the risk factors for confirmed neurocysticercosis were identified despite the abundance of case series of neurocysticercosis in the literature. An analysis of neurologic patients in Peru found an association between seropositivity and being born outside Lima, having raised pigs, older than 20 years old, a history of seizures, and a history of taeniasis.[189] A case control study of CT-confirmed NCC found an association with eating street food (OR=2.3) and a family history of NCC (OR=2.4).[190] Most field investigations studying the epidemiology of cysticercosis have analyzed serology defined by ELISA or EITB. Human seroprevalence measured by EITB ranges in endemic areas range between 2% and 34%, and in general is higher than if measure by ELISA.[179] Similarly to taeniasis, human cysticercosis seroprevalence cases cluster within households[14, 186, 187, 191] and within communities.[14] Several studies report that seroprevalence increases with age [14, 192] and does not present differences by sex.[14, 59, 179, 185, 186, 192-194]
43
Close proximity to an actual tapeworm carrier is the main risk factor for cysticercosis seroprevalence, although this factor was rarely analyzed as a risk factor in comparative epidemiological analyses. Being a confirmed tapeworm carrier is associated with a 4- to 18-fold increased odds[14, 59] and living with a carrier was associated with a 6- to 9-fold increase in seroprevalence odds.[181] Self-report of previously passing proglottids, on the other hand, was also associated with higher seroprevalence although not always as strongly as being a confirmed carrier (OR: 1.7 to 14.0).[187, 195-197] Other factors found associated in multiple studies were raising pigs (OR: 1.3 to 5.4),[14, 194, 197-199] absence of sanitary facilities (OR=1.9 to 2.9)[187, 195, 197, 199], less education (OR: 2.5 to 3.7)[194, 195, 199], and poor knowledge about the parasite (OR=2.4).[197, 199] Multiple factors were found associated in a single study: having infected pigs (OR=1.3),[14] lack of potable water (OR= 3.7),[199] dirt floor (OR=2.5),[199]
eating pork
frequently
(OR=1.6),[187]
not bathing
frequently
(OR=3.5),[187] eating street food (OR=3.6),[196] and not having a television set (OR=4.2).[200] Two studies were conducted among clearly unusual populations are worth describing separately. Among pork vendors, having daily contact with pork led to higher risk (40% vs. 0%),[198] while among Orthodox Jews in New York associated factors were female sex (relative risk [RR]=2.45), hiring a domestic worker for child care (RR=3.8) and having personnel from Central America (RR=2.7).[160] In one study that used multiple regression adjustment, the effect of raising pigs and having infected pigs [14] become not significant after the inclusion of living with a carrier.
44
II.6.3. Swine cysticercosis. Similar to human cysticercosis, swine infection originates from ingestion of T. solium eggs, although in most cases exposure arises due to the coprophagic behavior of pigs. The test of choice to assess swine cysticercosis exposure is EITB,[54, 55] although seroprevalence overestimates the actual presence of infection. The tongue test, on the other hand, is used in the field to evaluate actual infection, although its sensitivity is clearly lower. [83] Both EITB and lingual examination, however, are becoming more commonly used in epidemiological studies, and the risk factors identified in field studies are similar for both tests. Proximity to T. solium tapeworm carriers has not been analyzed in the studies reviewed in the literature, despite multiple anecdotic reports of tapeworm carriers that owned pigs with infection confirmed by tongue inspection.[182, 185] Similarly, the clustering of infection within households requires further study and only few studies have analyzed seroincidence.[95, 201] Analysis including multiple
regression-adjusted
estimates were more frequently published in recent years.[201-204] Porcine cysticercosis seroprevalence is high already at 2-4 months of age probably due to maternal antibodies, and increases with age.[14, 88, 187, 195, 201, 205, 206] Older pigs have lower seroincidence, and there were no differences associated to the sex of the pig.[201] Castration and pregnancy increased the odds of seropositivity.[205, 206] Other factors associated with increased risk in several studies were being a freeranging pig (OR: 1.7 to 10.3),[87, 185, 187, 202, 204, 206, 207] and having access to human feces (OR: 1.8 to 3.4).[87, 88, 185, 187] The absence of sanitary facilities was associated with higher risk in several studies (OR: 1.8 to 5.6),[195, 203, 206, 207] although pigs owned by households that had toilets were found to be at increased risk in
45
two studies.[88, 202] Being owned by large families (OR: 1.9 to 2.4),[202] home slaughter (OR: 4.0 to 6.1),[207] and being a native breed (OR=1.4)[206] were found to be associated with increased risk in only one study each.
II.7. EGG DISPERSION MECHANISMS Although most transmission probably occurs by direct contact between tapeworm carriers and susceptible hosts, cases of human and swine cysticercosis are often spread throughout multiple households and herds indicating substantial dispersion.[195] Such disseminated disease presence suggests either displacement of carriers and susceptible hosts or the action of egg dispersion mechanisms increasing contact between carriers and hosts. However, the possible role of dispersion mechanisms for T. solium transmission has been poorly studied. The last comprehensive review on this topic was published in 1983 [208] and little additional evidence has been generated since then. No proof exists to date about T. solium cysticercosis transmission through egg dispersion in field conditions. The consistent failure to find Taenia eggs in the soil near the homes of tapeworm carriers seems to suggest that egg dissemination mechanisms have a limited role in the transmission of T solium cysticercosis. A study evaluated 400 soil samples and found eggs and larvae of nematodes, coccidian and mites, but no Taenia sp. eggs. [184] Another study with 412 soil samples found helminth eggs in 2.6% of the samples but Taenia sp. eggs in only one.[187] In a third study, only one of 15 soil and dust samples from carriers' homes had eggs morphologically compatible with Taenia sp.[182] Another study in Peru evaluated five pools of soil samples from spots with high likelihood of contamination but again obtained negative results.[209] The interpretation of these
46
results, however, should consider the poor sensitivity of microscopy used to detect T. solium eggs in soil. A review of the main potentially contributing egg dispersion mechanisms is warranted before reaching final conclusions.
11.7.1. Wind. The outer surface of T. solium eggs is particularly sticky and keeps them trapped in fecal matter, making them unlikely to become airborne. Additionally, Taenia eggs are extremely sensitive to desiccation and may not survive until fecal matter dries, when the wind could disseminate them.[208] Additionally, T. solium proglottids lack the motility of other tapeworm species, [24] and probably require a dispersion mechanism stronger than the wind to disseminate them. Finally, T. hydatigena eggs presented a uniform radial dissemination around carriers without an association with wind spread, despite the known reliance of T. hydatigena on egg dispersion mechanisms.[16]
11.7.2. Birds. Although is unclear if birds can compete with pigs for access to human feces, there is evidence that seagulls and young chickens can ingest T. saginata proglottids and eggs and expel them intact.[210, 211] Gladkov (1969) also observed that crows and sparrows could support dissemination of Taeniid eggs.[212] However, T. solium proglottids are substantially less motile than T. saginata proglottids [24] and therefore potentially less noticeable to birds looking for food. However, these mechanisms remain as an open possibility to be explored.
11.7.3. Flies. Flies seem to be a natural mechanism to transport Taenia eggs due to their natural attraction to human and animal feces for feeding and breeding, but current
47
evidence does not suggest an important role in T. solium transmission. Zmeev (1936) and Nadzhafov (1967) found T. saginata eggs externally attached to different types of flies.[213, 214] Extensive laboratory and field evidence describes several types of flies able to provide internal carriage for T. saginata and T. hydatigena eggs,[208] including the confirmed transmission of T. hydatigena to lambs and pigs by blowflies.[215] More recently, however, two attempts to recover Taenia sp. eggs in domestic flies failed both from 600 fly specimens [184] as well as from the guts and legs of 180 flies. [216] In a second study on flies, no other parasite eggs were found either, suggesting that flies may not have enough feeding time on feces to ingest eggs.
11.7.4. Dung beetles. Dung beetles are another likely candidate for T. solium egg dispersal due to their intimate ecological linkage to fecal material.[208, 217] Zenkov (1978) observed viable eggs of T. solium over a period of 48 hours in coprophagous, leather beetles (Dermestes spp.) who ingest eggs with fecal material.[217, 218] Other species feed on proglottids and/or pick up eggs externally and viable T. saginata eggs have been found in their grubs.[219] However, available evidence on the flight range of these coleoptera is limited and suggests a short travel distance, compatible with the short dispersal range of Taenia eggs.[217]
11.7.5. Pigs. Gonzalez et al. described four different pieces of evidence that support the possibility that pigs that ingested viable T. solium eggs could transmit them to other susceptible pigs in their vicinity. [220, 221] Although it seems that this mechanism could explain part of the dissemination of T. solium eggs in the environment, the level of
48
contact between pigs in natural environment conditions may not allow for the transmission observed in controlled, laboratory settings.
II.8. CLUSTERING AROUND CARRIERS. Ingestion of T. solium eggs is the necessary cause to acquire human or swine T. solium cysticercosis. Egg ingestion mainly occurs by direct fecal-oral contamination in humans or coprophagia in pigs. Egg dispersion mechanisms probably allow transmission farther away from the immediate surroundings of carriers, although it has not yet been proven that egg dispersion substantially contributes to transmission rates in field settings. In most scenarios, close to each case of cysticercosis there is or there was a tapeworm carrier, and the presence of a current or former carrier should be the first risk factor to include when studying the epidemiology of cysticercosis. This crucial and necessary risk factor, however, has only been partially investigated in epidemiological field studies. Most evidence about the clustering of cysticercosis cases around tapeworm carriers was produced in experimental studies on T. hydatigena and T. ovis cysticercosis. These studies demonstrated not only increased risk surrounding carriers but also a clear gradient in risk at closer distances. However, it is unclear whether these findings can be extrapolated to T. solium cysticercosis mainly because sheep and cows are coprophobic[17, 208, 222] while pigs are coprophagic.[18, 19] This difference in the behavior of the intermediate host regarding feces completely alters the transmission dynamics of both porcine and ovine cysticercoses. T. solium transmission does not require an egg dispersion mechanism, while all the other cysticercoses do, and the ingested doses of Taenia eggs are probably substantially higher for swine cysticercosis.
49
The interpretation of existing evidence about the clustering of cysticercosis cases should consider these important differences in transmission dynamics.
II.8.1. Taenia solium cysticercosis. Three studies compared the risk associated with harboring a tapeworm carrier or living in the same house as a carrier including two crosssectional surveys conducted by Diaz-Camacho.[181] Subjects from randomly selected families had cysticercosis seroprevalences (ELISA) of 46% (8/13) and 8% (16/185) in families with and without confirmed carriers respectively (OR=9.1, 95% CI: 4.3 - 19.0). Among people from volunteer households, cysticercosis seroprevalence was 43% (13/30) and 10% (45/448) in families with and without confirmed carriers, respectively (OR=6.8, 95% CI: 3.1-14.9) Garcia-Noval et al. conducted a cross-sectional cysticercosis
study and determined
antigens with ELISA and taeniasis by microscopy and ELISA
coproantigen.[59] Cysticercosis seroprevalence was 29% (6/21) in confirmed T. solium tapeworm carriers versus 12% (157/1266) in non-carriers (OR=2.3, 95% CI: 1.2, 4.6). The seroprevalence in all Taenia carriers was 40% (14/35), 19% (20/107) in their household contacts, and 12% (173/1399) among residents of households without carriers. Contacts of carriers had slightly higher seroprevalence than non-contact individuals (OR=1.6, 95% CI: 0.9, 2.8) and carriers showed a non-significant increase in seroprevalence than their contacts (OR=1.7, 95% CI: 0.7, 4.1). Similar although significant increases in EITB seroprevalence around confirmed carriers by coproantigen and microscopy were observed by Garcia et al. in a cross-sectional study in Peru.[14] Seroprevalence among T solium tapeworm carriers was higher than among their
50
household contacts (23/30=77% vs. 22/55=40%, OR=4.9, 95% CI: 1.7, 15.7), and also was higher among contacts compared to residents of households without carriers (22/55=40% vs. 111/832=13%, OR=4.3, 95% CI: 2.3, 8.0). Four studies assessed the association between cysticercosis and passage of proglottids, and the strongest association was observed when cysticercosis was defined with more specific clinical and imaging criteria. Sarti conducted a cluster sample, crosssectional study in Mexico assessing seroprevalence by EITB and taeniasis by microscopic examinations. Four subjects excreted Taenia sp. eggs out of a total of 1552. Seroprevalence was 20.6% and 10.3% in subjects reporting having passed proglottids (n=90) or not (n=1462), respectively (OR=2.3, 95% CI=1.2, 4.4). Cao et al. conducted a population-based case-control study in Shandong province, China. [197] Forty-eight neurocysticercosis cases with two or more positive criteria (serology, symptoms, imaging or increased CSF pressure or presence of leukocytes/proteins) were compared to four age/sex-matched controls each. A history of passing proglottids was reported by seven cases (15%) and two controls (1%), a 14.0 unadjusted odds ratio. The odds ratio became 9.2 (95% CI: 1.2, 136.9) after adjusting by defecation habits, allowing pigs to feed on human feces and being unable to identify infected meat. Garcia-Garcia et al. conducted a case-control study in 117 relatives of soldiers positive for either cysticercosis (ELISA/Western Blot) or taeniasis (ELISA) compared to 110 relatives of negatives soldiers matching soldiers by age, gender, rank, education, residence and type of work. [196] A history of passing proglottids was reported by 12% and 4% of the relatives of positive and negative soldiers, respectively (OR=3.6, 95% CI: 1.0, 14.0). Carrique-Mas et al. conducted a cross-sectional study in the El Chaco zone of
51
Bolivia, and assessed taeniasis by microscopy and cysticercosis seroprevalence in humans by ELISA.[195] Five tapeworm carriers were found, and the seroprevalence was 30% (45/149) and 20% (32/159) in people who reported passing proglottids or not, respectively (OR=1.7, 95% CI: 1.0, 3.0). In Peru, Garcia et al. observed a minor increase in seropositivity by EITB associated with a history of passing proglottids (36/218=17% vs. 319/2364=13%, OR=1.3, 95% CI: 0.8, 1.9), that was significant only among subjects >25 years old (OR=2.8, 95% CI: 1.8, 4.1).[14] II.8.2. Experiments on T. hydatigena. Two experiments conducted and a semiexperimental study reported by Gemmell et al. confirmed the spontaneous dispersion of T. hydatigena and T. ovis eggs around tapeworm carriers. These studies also demonstrated the clustering of increased infection rates surrounding carriers and the presence of a gradient of parasitic burden related to the distance to carriers. In the first experiment, a dog with four confirmed T. hydatigena tapeworms was chained to a kennel at the end of strip of pasture, and seven wire-fenced pasture plots were created at different distances from the kennel.[15] Five lambs were grazed for 10 days before and after the introduction of the dog in each of the seven plots, and were necropsied three months later to determine cyst counts per animal. Table 4 shows that cyst counts after introducing the dog increased significantly in plots up to 80m from the carrier. Low but non-zero cyst counts were observed both before the introduction of the dog as well as far from the kennel after introducing the carrier. Results of the three plots farther away from the kennel are presented aggregated because no evidence of increased transmission was found that far from the carrier.
52
Table 4. Cyst counts in grazing lambs before and after introducing a T. hydatigena tapeworm carrier. Based on: Gemmell MA, Johnstone PD. Factors regulating tapeworm populations: dispersion of eggs of Taenia hydatigena on pasture. Ann Trop Med Parasitol. 1976 Dec;70(4):431-4. Distance to the kennel (m)
Time Before Infected / Total Cysts (Mean ± SD)
0-25*
26-80*
81-130
131-190
191-370
2/5
2/5
3/5
4/5
12/15
0.8
1.0
2.2 ±2.4
10.6 ± 14.7
1.3 ±2.2
5/5
5/5
5/5
5/5
5/15
After Infected / Total tysts(Mean±
8 9 0 ± 4 1 7
g_8 ±
7 6
3.0 ±1.8
2.0 ±1.4
0.5 ±0.8
Figure 8. Layout of grazing plots. Based on: Gemmell MA, Johnstone PD. Factors regulating tapeworm populations: dispersion of eggs of Taenia hydatigena on pasture. Ann Trop Med Parasitol. 1976 Dec;70(4):431-4.
53
A component of a second experiment provided additional results about the clustering of T. hydatigena infection around carriers.[16] Four dogs were placed for ten days in a 36m square kennel; three of them harbored confirmed T. hydatigena tapeworms. A grazing circle was devised, composed of two circular, concentric grazing zones were prepared around the kennel (6-21.6m and 21.7-30m), each divided grazing zone in nine identical, double-fenced grazing plots (Figure 8). Two sheep grazed in each plot for 10 days and were necropsied eight weeks after grazing. Average cysts counts appear to be uniform in all directions irrespective of wind and ground conditions. The average cyst count within 6-21.6m from the carriers was non-significantly higher than within 21.6-30m from the kennel (38.3±59.7 vs. 25.7±39.9). Additional evidence of the dispersal and clustering of cysticercosis arose when heavily infected lambs were unexpectedly found in a farm located adjacently to the research unit where the two experiments described about were conducted. [208] Sentinel sheep were placed in the plots for two months, and significantly higher T. hydatigena and T. ovis cyst counts were found during necropsy in animals nearer the dog kennel (Figure 9). The increasing parasitic burden at closer distances suggested that the kennel was the potential epicenter of this outbreak. Under this hypothesis, egg dispersal could have occurred up to 175m from the carriers.
54
Figure 9. Taenia hydatigena and T. ovis cyst counts found in an investigation of an accidental outbreak of cysticercosis. As presented in Lawson JR, Gemmell MA. Hydatidosis and cysticercosis: the dynamics of transmission. Adv Parasitol. 1983;22:261-308. Permission requested from the journal.
— Hedge
55
II.9. PREVENTION AND CONTROL In 1993, the International Task Force for Disease Eradication (ITFDE) listed T. solium cysticercosis as one of the six potentially eradicable diseases among a total of 100 pre-selected infectious conditions.[223] Ten years after, the ITFDE evaluated the progress in this rather ambitious goal, recognizing the existence of successful pilot demonstrations of control measures in Ecuador, Mexico and Peru. ITFDE2 concluded, however, that the proof of principle for the elimination or even control of T. solium infection at a national scale had yet to be shown. Its recommendations include the need for an improved understanding of the prevalence, economic impact, and transmission dynamics of T. solium. Additionally, the Task Force encouraged the evaluation of the impact of mass distribution of praziquantel and albendazole for the control of cysticercosis/taeniasis.[224]
The elimination of cysticercosis in developed countries was most likely the results of improvement in economic and sanitary conditions, including improved pig husbandry and regular meat inspection. [24] Such changes, however, cannot be expected to occur in the developing world in the near future,[183] and interventions such as indoor/corralled pig husbandry cannot be introduced promptly nor effectively in endemic settings.[183] Free-range pigs minimize expenses on food, and small farmers are unlikely to abandon this practice unless there is a strong economic incentive to alter it. [72] Meat inspection is severely limited by its low coverage, the extended practice of assessing infection by tongue examination before deciding where to sell pigs, and parallel marketing channels for cysticercotic animals.[91, 183] Only a few control approaches have been
56
implemented in the developing world as part of research trials with varied immediate results and long-term impact.
II.9.1. Mass chemotherapy. Encouraged by the success of mass chemotherapy to treat the adult carrier in the control of echinococcosis and ovine cysticercosis, this approach was promptly extended to the control of T. solium cysticercosis. Mass chemotherapy for T. solium cysticercosis has been implemented mainly in the Americas, and the use of praziquantel or niclosamide initially led to promising results. Combined targeting of both cysticercotic pigs and human tapeworm carriers[225] was added later. Swine chemotherapy with oxfendazole as a mass chemotherapy option[124, 147-149] was expected to lead to achieve elimination faster and with higher chances of success.
The results of mass chemotherapy interventions, either on taeniasis alone or combined with targeting swine cysticercosis, have been disappointing at best. The only published controlled trial to date showed reductions in swine seroprevalence and seroincidence that were far from ideal. [201] Part of the reason for the limited success of mass chemotherapy may derive from differences between the epidemiological stabilities of each cestodiasis.[226] T. hydatigena, for example is transmitted mainly in endemic state and mass chemotherapy drives it to extinction status, while T. solium is normally found in hyperendemic state and may only be driven to endemic state.[227] Additionally, only two studies have evaluated post-intervention sustainability, each with only partial success.[201, 228] The main chemotherapy-based control interventions documented to date are presented here.
57
11.9.1.1.
CHINA. AS
reported by Allan and quoted by Pawlowski, it appears that
the earliest evidence about the effectiveness of mass tapeworm treatment originates from China. Between 1983 and 1987, a combined intervention was conducted using bi-annual treatment with praziquantel, pig restraint and health education. Although no formal results have reached the international literature, it has been reported that the prevalence of taeniasis dropped from 1512 per 100,000 to 21 per 100,000, and the prevalence of swine cysticercosis dropped from 7.7% to 0.3%.[178, 229] 11.9.1.2.
MEXICO.
Three trials have been conducted in Mexico with varied
methodologies and results. In 1989, Keilbach et al. reported the effect of a mass treatment intervention using praziquantel at 5 mg/kg and education in a rural village in Guerrero (population: ~900p, coverage = 85%). The prevalence of Taenia sp. eggs by stool microscopy dropped in one year from 3.2% to 1.0%, but swine seroprevalence determined with tongue examination increased from 6% to 11%.[184] In 1988-9, Diaz-Camacho et al. conducted a mass treatment intervention with praziquantel (10 mg/kg) in a rural village in Sinaloa (population = 559, coverage = 70%). The prevalence of taeniasis dropped from 1.3% to 0% one year after treatment, and the prevalence of human seropositivity by ELISA dropped from
11.0% to 7.1%. Swine cysticercosis assessed by tongue
examination went from 1/72 to 0/57.[182] Finally, in 1991 Sarti et al. implemented a mass treatment program for human taeniasis in Atotonilco (population = 3007, coverage = 87%) with a single dose of praziquantel (5
58
mg/kg). Taeniasis by ELISA and microscopy dropped from 1.1% to 0.5% in 6 months, remaining at 0.5% three years after, while human cysticercosis seroprevalence by EITB first increased from 5.7% to 10.1% and then dropped to 2.2%. Swine cysticercosis measured by tongue examination had a sustained decrease (1.2%, 1.1% and 0.6%, respectively) but not according to EITB (4.8%, 2.2% and 3.4%, respectively.[228] 11.9.1.3.
ECUADOR.
Between 1985 and 1987, Cruz conducted a large taeniasis
mass treatment intervention in two provinces (population = 13,416, coverage = 76%) giving a single round of praziquantel at 5 mg/kg body weight. Taeniasis rates decreased from 2.2% to 0.5% in a small area where follow-up was conducted. Swine prevalence in slaughtered pigs dropped from 11.4% to 2.6%.[183] 11.9.1.4.
GUATEMALA.
In 1995, Allan and colleagues treated residents of two
communities in Jutiapa (population = 2119, coverage = 75%) with a single dose of niclosamide (2g for subjects > 6 years old, lg otherwise). Taeniasis by ELISA and microscopy dropped from 3.5% to 1.0% in 10 months, while swine seroprevalence by EITB dropped from 55% to 7%.[180] 11.9.1.5.
PERU.
The Cysticercosis Working Group in Peru has conducted to date
three combined mass chemotherapy interventions to humans and pigs, although the results of the second and third intervention are not yet available. In 1996, Garcia et al. implemented the first combined mass treatment intervention near Huancayo (population = 5678, coverage = 75% for taeniasis and >90% for swine cysticercosis). Swine seroprevalence and seroincidence was evaluated eight times,
59
every four months using EITB and five times after the intervention was delivered. Regression-adjusted
reductions
in
swine
seroprevalence
(OR=0.51)
and
seroincidence (OR=0.39) were reported, but the magnitude of the decrease was clearly unsatisfactory and far from achieving interruption of transmission. [201] Incomplete coverage, treatment failure and reintroduction of infection were the potential reasons accounting for the lack of effect. Gonzalez et al. reported preliminary results from a second combined mass intervention conducted in eight villages in Tumbes. Two niclosamide treatment rounds and four rounds of swine treatment with oxfendazole were provided every three months (population: ~900). No new swine infections were detected in two of the villages and a clearly decrease incidence was observed in the other five, but new porcine cases were observed six months after the second taeniasis mass treatment.[227] Currently, the Bill and Melinda Gates Foundation is supporting another project, also in Tumbes, to demonstrate the feasibility of the elimination of cysticercosis/taeniasis. Several control approaches are being tested including education and different combined chemotherapy schemes.[72, 221]
II.9.2. Education. In 1992-3, Elsa Sarti and her colleagues conducted the only cysticercosis control intervention based solely on health education in Chalcatzingo, Mexico (population = 1931). The educational intervention lasted six months and addressed the life cycle of the parasite and modification of risk behaviors. Educational activities reached schools, health facilities and households and community organizations. After the intervention, awareness about cysticercosis and taeniasis increased and this
60
effect was observed six months after the educational campaign concluded. Knowledge of the life cycle before and after the intervention was poor, and did not present a significant increase. Responses about hygiene behaviors appeared to be affected by social desirability and did not correlate with observed behaviors. Despite no evidence of effect in actual knowledge, the prevalence of swine cysticercosis dropped from 2.6% to 0% and 5.2% to 1.2% when assessed by tongue inspection and EITB, respectively. A nonsignificant reduction in taeniasis assessed by ELISA was also observed.[230] Research found that taeniasis-cysticercosis is not considered an important health problem in the community. In an intervention with an educational component in Mexico, only children improved their knowledge about the disease but adults showed no improvement. [184] Diaz-Camacho also noted that inhabitants were aware of swine cysticercosis {'ladillas') but did not link them with the tapeworms or with any disease threat. [182] Finally, risk behaviors such as outdoor defecation and eating infected pork did not decrease in the expected magnitude even after several years of intervention. [228]
II.9.3. Vaccination. Significant progress has been recently achieved in the development of efficacious vaccines against swine T. solium cysticercosis. The most encouraging results have been obtained using recombinant oncosphere antigens identified following the same approach that led to the development of an effective vaccine for T. saginata in cows.[231] Two candidate antigens, TSOL18 and TSOL45, have been tested in randomized trials, and both reached efficacy >97% against oral challenge.[125, 232] To date, separate research groups have conducted five highly successful evaluations in Mexico, Peru, Cameroon and Honduras. The TSOL18 antigen seems to be the most
61
effective, having reached >99% protection against high-dose challenges in each of the trials conducted.[233] Current research is focusing on optimizing duration dose, determining the appropriate dose, schedule and adjuvant, and demonstrating protection of neonates. Effectiveness field trials are expected to follow in the future. [234]
62
Chapter Three
SWINE CYSTICERCOSIS HOTSPOTS SURROUNDING TAENIA SOLIUM TAPEWORM CARRIERS
Andres G. Lescano,1"3 Hector H. Garcia,1'2'4 Robert H. Gilman,1'2'5 M. Claudia Guezala,6 Victor C. W. Tsang,7 Cesar M. Gavidia,2'6 Silvia Rodriguez,4 Lawrence H. Moulton,2 Justin A. Green,8 and Armando E. Gonzalez 2'6 for the Cysticercosis Working Group in Peru
1. Universidad Peruana Cayetano Heredia, School of Public Health and Administration (AGL) and Department of Parasitology (HHG, RHG), Lima, Peru 2. Johns Hopkins Bloomberg School of Public Health, Department of International Health, Baltimore, Maryland 3. United States Naval Medical Research Center Detachment, Public Health Training Program, Lima, Peru 4. Instituto de Ciencias Neurologicas, Cysticercosis Unit, Lima, Peru 5. Asociacion Benefica PRISMA (Proyectos en Informatica, Salud, Medicina y Agricultura), Research Department, Lima, Peru 6. Universidad Nacional Mayor de San Marcos, School of Veterinary Medicine, Lima, Peru 7. Centers for Disease Control and Prevention, Division of Parasitic Diseases, Atlanta, Georgia
63
8. Imperial College, Department of Infectious Diseases, London, United Kingdom
Word count: 3,397 (abstract 149)
Tables: 4
Figures: 2
References: 31
Running Title: Swine cysticercosis hotspots around tapeworm carriers
Keywords: Taenia solium, cysticercosis, epidemiology, geographic information systems, incidence, prevalence, western blotting, splines, swine, Peru
Acknowledgments
We want to thank the population of Matapalo and local health workers for their support and cooperation. This study was partially funded by research grants numbers P01 AI51976 and U01 AI35894 from the National Institute of Allergy and Infectious Diseases, NIH, USA. Research grants from the Wellcome Trust (063109), the Food and Drug Administration (002309) and the Bill and Melinda Gates Foundation (23981) fund ongoing cysticercosis research by the authors. The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official or reflecting the views of the United States Department of the Army or Navy or any of the other organizations listed.
64
III.l. ABSTRACT We estimated the Taenia solium swine cysticercosis risk gradient surrounding tapeworm carriers in seven rural communities in Peru. At baseline, the prevalences of taeniasis by microscopy and swine cysticercosis by serology were 1.2% (11/898) and 30.8% (280/908) respectively. The four-month cumulative seroincidence was 9.8% (30/307). The unadjusted swine seroprevalence and seroincidence rates increased exponentially by 12.0% (95% CI: 9.7%-14.3%) and 32.8% (95% CI: 25.0%-41.0%) respectively when distance to carriers decreased by half. Swine seroprevalence was 18.4% at >500m from a carrier, 36.5% between 51-500m5 and 68.9% within 50m (p9
1.00 2.07
1.72-2.48
8 (3rd tertile)
1.00 1.41
1.12-1.78
0.004
1.12
1.09-1.16
3 positive EITB bands, as stronger EITB positivity is associated with greater parasitic burden and more severe infection,[70, 193] and 2) lifetime overall seizure prevalence, either NCC or non-NCC related. All statistical analyses were performed using Stata 9.2 (Stata Corporation, College Station, TX) and all confidence intervals (CI) were calculated at the 95% level. Maps were prepared with ArcMap 9.0 (Environmental Sciences Research Institute, Redlands, CA).
IV.4. RESULTS IV.4.1. Census The baseline census registered 1004 people and 237 families. We excluded 106 subjects from the analyses: 12 due to incomplete GPS measurements, 54 because they did not reside in the study area, and 40 temporary residents who stayed
.
SjSO
9? Q. o .*.
••
•.
'*
. . • . ; - s
•
•
/
o
• •
CM
' * ..
*\#
• —
•
• •
o - • 1
I
I
I
1
2
4
8
• •••••
at • " » t—mmt • • • M n A . • . »
50m Tapeworm carriers Household contacts Total
All seizures % p.vaiue n / N
NCC-related seizures n/N % p-value
2/42 2/80 38/716
2.4 2.5 5.3
0.604
2/42 1/80 23/715
2.4 1.2 3.2
0.629
0/11 2 / 31
0.0 6.5
0.992
0/11 1 / 31
0.0 3.2
0.996
42/838
5.0
25 / 837
3.0
In the analysis of secondary outcomes, seroprevalence defined by the presence of three or more positive EITB bands increased 13% each time distance to the nearest carrier halved (95% CI: 6%, 22%, Wald test p=0.002). The seroprevalence distance gradient, however, was observed only within 50m of carriers. There were no differences between >50m and l-50m from a carrier (62/693=8.9% vs. 5/71=7.0%, Wald test p=0.637), but seroprevalence increased from 7.0% in l-50m to 14/39=35.9% at the carriers' home (PR=4.01, 95% CI: 2.32-6.93, Wald test pO.OOl). Additionally, carriers had significantly higher seroprevalence than their household contacts (8/11=72.7% vs. 6/28=21.4%, PR=3.39, 95% CI: 1.48-7.80, Wald test p=0.004). The prevalence of all seizures, in contrast, was not associated to the distance to the nearest carrier, neither as the base 2 logarithm of the distance nor when analyzed by distance ranges (Wald test p=0.842 and p=0.604 [2 DF], respectively).
100
Table 10. Covariate associations with the seroprevalence of human cysticercosis, Tumbes, Peru, 1999 Positive
Tested
Prevalence
Prevalence ratio (PR)
Village Tutumo Leandro Campos Nuevo Progreso Matapalo Isla Noblecilla Quebrada Seca Totora
24 18 33 59 12 26 24
118 83 147 239 47 94 75
20.3 21.7 22.4 24.7 25.5 27.7 32.0
1.00 1.07 1.10 1.21 1.26 1.36 1.57
Age (years) 0-9 10-19 20-29 30-39 40-49 50-59 60+
38 41 37 33 11 22 14
148 199 145 131 54 61 65
25.7 20.6 25.5 25.2 20.4 36.1 21.5
1.00 0.80 0.99 0.98 0.79 1.40 0.84
Gender Female Male
88 108
347 456
25.4 23.7
1.00 0.93
Owns pigs* No Yes
36 146
119 611
30.3 23.9
1.00 0.79
# pigs* Doesn't own pigs 1-3 (1st fertile) 4-7 (2nd fertile) >7 (3rd fertile)
36 36 55 55
119 169 201 241
30.3 21.3 27.4 22.8
1.00 0.70 0.90 0.75
% seropositive pigs* Doesn't own pigs 50.0% (3rd fertile)
36 41 42 63
119 208 226 177
30.3 19.7 18.6 35.6
1.00 0.65 0.61 1.18
Households within a 100m radius 1-3 (1st fertile) 4-8 (2nd fertile) >8 (3rd fertile)
61 77 58
321 260 222
19.0 29.6 26.1
1.00 1.56 1.37
Crowding (people/room)* 0 . 3 - 1 . 2 (1st fertile) 1.3 - 2 . 2 (2nd fertile) >2.2 (3rd fertile)
29 63 80
132 278 336
22.0 22.7 23.8
1.00 1.03 1.08
Latrine in household* No Yes
125 61
520 259
24.0 23.6
1.00 0.98
_
_
_
1.12
tapeworm 187 9
792 11
23.6 81.8
1.00 3.47
196
803
24.4
Variable
Total
r,'
Multivariate adjusted** PR p-value*** 95% CI
0.593
0.624 1.00 1.09 0.79 0.79 0.91 0.83 1.14
-
0.59-2.03 0.47-1.33 0.45-1.39 0.45-1.86 0.46-1.48 0.62 - 2.08
0.313
0.098 1.00 0.74 0.97 0.95 0.84 1.50 0.71
-
0.49-1.10 0.65-1.45 0.62-1.44 0.45-1.55 0.96 - 2.36 0.42-1.19
0.584
0.370 1.00 0.89
-
0.69-1.15
0.143
0.716 1.00 0.93
-
0.63-1.38
0.241
0.846 1.00 0.84 1.00 0.93
-
0.51 - 1 . 3 6 0.64-1.56 0.60-1.45
500m
Figure 17b. Swine seroprevalence 100 *
80
o> u c V
«
>
60
Q.
o
40
a> c
20
V (0
54 19 ?1 bands
?3 bands
H Carrier's home • 2 - 5 0 0 m D > 500m
122
Table 14. Risk factors for the presence of one or more viable T. solium cysts on swine, Tumbes, Peru, 2005 Bivariate Analysis PR p-value Ref 23.62 0.003 500m 2-500m Carriers' home
Viable Infection n/N % 1/222 0.5 10/94 10.6 7/10 70.0
Degenerated cysts
No Yes
8/295 10/31
2.7 32.3
Ref 11.90
Swine age
=10
3/183 15/143
1.6 10.5
Female Male
13/179 5/147
Households within 100m
0-2 >2
Poverty
Covariate
PR
Multiple Regression 95% CI p-value
6.55 48.67
0.63,68.07 5.28,449.00
0.116 0.001
500m and 2-500m of a carrier (95% CI: 0.6-68.1, p=0.116, Wald test) and 7.4 times between 2-500m and the carriers' home (95% CI: 4.2-13.3, p500m and 2-500m (PR=1.1, 95% CI: 0.8-1.5, p=0.472) but there was a clear increase from 2-500m to the carriers' home (PR=1.6, 95% CI: 1.3-2.1, p500m to 2-500m (PR=1.4, 95% CI: 0.7-2.8, p=0.379) with a sharper difference 2-500m to the carriers' home (PR=3.8, 95% CI: 2.0-7.1, pO.OOl). The number of EITB bands in seropositive pigs was inversely correlated with the distance to the nearest carrier, and pigs closer to tapeworms had more seropositive bands (Spearman's Rho = -0.17, p=0.022).
124
V.5. DISCUSSION Our results show significant clustering of viable swine cysticercosis infection near T. solium tapeworm carriers with 70% infection prevalence in swine owned by carriers and 11% within 500m of them. The prevalence of infection among pigs owned by carriers are 155 times higher than among swine living >500m from them. These findings provide direct evidence that previously observed swine seropositivity hotspots around carriers[244, 257] do correlate with actual clusters of infection, and illustrate the potential of tapeworm carriers to contaminate their homes and immediate surroundings. The dispersion patterns of T. ovis and T. hydatigena have shown similar clustering around carriers, despite the coprophobic behavior of sheep, providing additional support to the validity of our conclusions.[15, 208] On average, pigs with degenerated cysts were found farther from current tapeworm carriers compared to swine with viable infection. Looking specifically at herds located >500m away from carriers, non-viable infection was almost 12 times higher than viable infection (6% vs. 0.5%). It seems unlikely that current carriers would have infected all of those additional herds with non-viable cysts, either directly or through egg dispersion mechanisms, because such herds are too far away from carriers. Such distant pockets of non-viable infection may result instead from tapeworms once present near those herds, but who either died or the carrier migrated. Cysts usually form 2-3 months after exposure [23] and start to degenerate several months later, [4] so it is conceivable that months to years after, clusters of non-viable infection could be observed in the place where a carrier once lived. That would also explain why multiple pigs in one herd had degenerated cysts and why multiple infected herds are found in close proximity to each
125
other. Clusters of pigs with degenerated cysts only, particularly if far from detected carriers, may suggest in some cases close proximity to the location of a former carrier. Although viable infection clearly clusters around tapeworm carriers, some animals with viable infection were not found in the immediate proximity of carriers, suggesting that egg dispersion mechanisms could play a role in the transmission of T. solium cysticercosis. However, our understanding of this issue is very limited and little progress has been achieved since a landmark review was published in 1983. Recent evidence has disregarded the role of flies in egg dissemination,[216] and many attempts to collect T. solium eggs in soil and water[182, 184, 187, 209] suggest that dispersion may be limited. Gonzalez described that secondary cysticercosis transmission from pig to pig can occur,[220, 221] and there is great interest in the role of dung beetles, a potential mechanism reported many years ago [208] but that has not been reassessed until now. Clearly this is little explored area in transmission dynamics, and information regarding the actual possibility of transmission through these mechanisms is needed. The low prevalence of taeniasis[198, 261] and aggregation of tapeworm carriers within households[13] often limit the sample size and statistical power of studies associating cysticercosis risk to the presence of carriers. Additionally, the actual viability of cysts was not rigorously assessed and a few cysts may have been incorrectly classified as viable or degenerated. However, we observed a highly significant association between distance to the carrier and viable infection, and confirmed observations made in a different area and period using a smaller sample size than in our previous work. [244, 257] Also, we used a highly specific, gold standard measure of disease-burden, the presence of T. solium cysticerci determined by necropsy, and obtained findings clearly
126
consistent with previous evidence. Finally, the hypothesis of cysticercosis clustering around carriers has strong biological plausibility and has already been confirmed for T. ovis and T. hydatigena.[\5, 208]. Although our results could be explained by random chance, misclassification or biases, the consistency of our conclusions with the scientific literature suggests this possibility is unlikely. In this study, the seroprevalence rates observed at different distance to tapeworm carriers did not show the statistically significant gradient observed in a previous study,[244] particularly between 2-500m and >500m from carriers. Although the absence of a difference could be due to chance or the smaller sample size in this study, it could also be due to the high seroprevalence observed. The swine seroprevalence in this study (57%) nearly duplicates the 31% reported in Matapalo[244] and ranks among the highest ever reported together with the 62% reported in Huancayo, Peru. [14] In such hyperendemic settings, the chances of exposure and therefore formation of antibodies are probably uniformly high everywhere. The presence of a tapeworm carrier, therefore, may not alter substantially the already high seroprevalence farther away from its immediate vicinity. The rural, disperse conditions of the study area, on the other hand, could also reduce the likelihood that pigs find tapeworm carriers in their surroundings. To study the aggregation of human and swine cysticercosis around carriers in this and previous studies,[244, 257] we followed a method that can be generalized to other studies of the distribution of disease surrounding a few potential infection sources. We calculated the distance between subjects and potential sources and used generalized linear models[240] to assess changes in disease frequency when subjects get closer to those sources. Additionally, in the two previous studies we used splines to describe the distance
127
gradient, therefore avoiding preconceptions or arbitrary decisions when modeling the shape of the distance gradient. [262] A key advantage of our approach is to express the disease-distance gradient in easily interpretable measures of strength of association such as prevalence and incidence rate ratios. Additionally, the use of GLMs allowed modeling the distance gradient, and provided regression models not directly available in most spatial statistics software, a tool crucial to adjust disease-distance gradients by other covariates. Both splines and GLMs are implemented in most commercial statistical software and therefore fairly accessible. Further improvement of our approach is clearly needed, for example to estimate the average distance within which clustering occurs using a regression-based method, or to estimate the individual contribution of each potential infection source. However, in general we believe that the methods used here can be a fairly straightforward, understandable and flexible approach to assess diseasedistance gradients. In summary, we demonstrated clustering of swine cysticercosis infection in the immediate surroundings of confirmed T. solium tapeworm carriers and showed transmission patterns relevant for control interventions. We found that approximately 95% of all pigs with viable cysticercosis were found within 500m of a carrier and -40% were actually owned by a family with a tapeworm carrier. Pigs infected with healthy T. solium cysticerci are capable of supporting further disease transmission and these infection foci should be targeted by control interventions. The strong concentration of viable infection in the proximity of tapeworm carriers may allow us to focus our interventions thus improving both their efficacy and cost-effectiveness.
128
Chapter Six
INTEGRATED DISCUSSION
VI.l. CONCLUSIONS
Our results consistently show strong clustering of swine and human cysticercosis surrounding T. solium tapeworm carriers and confirm that carriers are the epicenter of cysticercosis hotspots where increased numbers of infected pigs and humans coexist. Swine seroprevalence increased from 18% at >500m from a tapeworm carrier to 69% within 50m of the carriers' homes, and swine seroincidence increased from 4% to 40%. Human seroprevalence increased from 21% >50m from a carrier to 64% at the homes of carriers. Viable swine infection, the most reliable marker of actual transmission potential, increased from 0.5% at >500m from confirmed T. solium carriers to 70% at the carriers' homes. These results
corroborate
evidence of increased
human
cysticercosis
seroprevalence at the homes of carriers,[14, 59, 181] and expand it by demonstrating that swine seroprevalence and infection are also increased around carriers.
In addition to clustering at the carriers' homes, all swine risk markers as well as human
seroprevalence
showed
a significant,
monotonic
cysticercosis
gradient
surrounding confirmed T. solium tapeworm carriers. Swine cysticercosis seroprevalence and seroincidence in pigs living 50-500m from carriers were significantly higher than in pigs at >500m, but lower than in pigs living within 50m of carriers. Similar findings were
129
observed for viable swine infection and human seroprevalence. Experimental infection rates in T. hydatigena and T. ovis also presented similar distance gradients[15, 16, 208] despite the known differences in transmission mechanisms of these taeniids compared to T. solium. The increased risk present in the carriers' immediate surroundings suggests that high-risk hotspots are not limited to the homes of carriers. Our results show that high-risk hotspots can extend up to 500m from carriers, and increased chances of cysticercosis exposure and infection can be seen in the carriers' neighbors and their porcine herds. These hotspots provide an opportunity to target most of the T. solium infection potential in the human and porcine hosts in a single intervention without having to reach every corner of the disperse, rural areas where cysticercosis is endemic.
The main approach used in field trials of cysticercosis control has been mass treatment, either for human taeniasis alone[180, 182-184, 228] or targeting swine cysticercosis as well.[72, 201, 221, 227] Targeting interventions to confirmed T. solium transmission foci defined by the presence of both infected hosts, human tapeworm carriers and cysticercotic pigs, was proposed recently as a potentially viable and costeffective approach. [10, 224, 263, 264] The impact of targeted interventions, however, is not well known. Observations of Craig et al. reported that a combined, targeted intervention in Zhangye, China between 1978 and 1988 reduced both the incidence of taeniasis and swine cysticercosis. However, these results were never formally published in the peer reviewed literature,[178] and apparently no other targeted interventions have been conducted. Targeted interventions, however, have been effective prevention and control strategies for other infectious diseases. Mop-up vaccination, i.e. intensified ring
130
vaccination around confirmed transmission foci, was key in the last stages of smallpox eradication[265] and is a major reason for the progress achieved towards poliomyelitis eradication. [266] Additionally, targeted outbreak response to transmissible, highly pathogenic H5N1 influenza could either contain a potential pandemic or at least delay international spread according to WHO.[267-269] The success of targeted control in smallpox and polio eradication processes encourages its use for cysticercosis, another potentially eradicable disease.[270]
Several key factors should be considered to devise and pilot focused interventions. A key decision is which control measure or measures should be applied to humans and pigs. Anti-helminth drugs are the control intervention of choice for taeniasis,[129] but either chemoprophylaxis or vaccines could be considered for pigs. The effectiveness of mass swine treatment with oxfendazole has been only partially effective at best, and the observed reductions in seroprevalence and seroincidence have been fairly disappointing. [201, 227] Vaccines, on the other hand, have shown high efficacy in controlled laboratory settings[125, 232] and focused interventions could be an avenue to assess their efficacy in field conditions.
Another potentially important parameter is the size of the intervention area. The observed swine infection gradient suggests that interventions could be delivered within 500m of carriers, as infection rates in that range were higher than >500m and nearly all pigs with viable infection lived within that radius. The gradients of swine cysticercosis seroprevalence and seroincidence also show clustering within 500m of a carrier, although
131
the aggregation was less evident in hyperendemic conditions. In general, the actual intervention radius ideally would be somewhere in the 50-500m range but could be ultimately defined according to available resources and geographic features of the pilot intervention region.
The life cycle of T. solium cysticercosis has been well described since the experiments of Kuchenmaister.[20] The risks associated with either harboring a tapeworm or living in close proximity to a carrier are well understood. In human cysticercosis, patients with symptomatic disease are known to have substantially increased rates of taeniasis compared to the general population. Additionally, harboring a tapeworm is related to severity of infection.[243] However, the proximity to a tapeworm carrier has not been analyzed in epidemiological studies as a risk factor for swine cysticercosis. We observed sharp gradients in swine seroincidence and viable infection around carriers, with 10-fold and 20-fold increases in the two rates when comparing pigs >500m from carriers to pigs immediately near carriers. These increases are the largest differences in seroincidence and infection rates reported. Consistent with knowledge about the life cycle of the parasite, our findings indicate that proximity to tapeworm carriers is the most important risk factor to acquire swine cysticercosis and should be studied in all field investigations. Similarly, studies of human cysticercosis epidemiology should attempt to assess the proximity of individuals to current or former tapeworm carriers.
132
Swine seroincidence and viable infection had a sharper gradient around carriers than swine and human seroprevalence, and no observable gradient was detected in neurocysticercosis-related seizure cases. This pattern demonstrates that recent exposure clusters stronger around current carriers. The risk gradient apparently blurs over time until it becomes undetectable years later, probably diluted by population dynamics, migration, disease progression and additional incident tapeworm carriers. Investigations of recent cysticercotic infections, therefore, should look for the current presence of a T. solium tapeworm carrier in close contact with cases. A history of passing proglottids among subjects in contact with cases, on the other hand, is probably a better risk factor for older exposure, such as cysticercosis seroprevalence, degenerated cysts, or cysticercotic seizures. This association has been significant in multiple observational studies of human cysticercosis seroprevalence. [14, 195-197]
We observed human and swine cysticercosis seroprevalence in a high proportion of all households and herds, respectively, and a similarly disseminated exposure pattern was reported in other hyperendemic settings.[195] A fraction of this highly spread exposure appears to result from direct egg ingestion via fecal-oral contamination in humans or coprophagia in pigs. Cases aggregate frequently within households[14, 186, 187] and herds[95, 201] and such clustering probably arises from shared exposure opportunities and common risk factors. The role of Taenia egg dissemination mechanisms, however, and their contribution to seropositivity and established infection remains poorly understood. There is evidence that pigs themselves and dung beetles disseminate viable T. solium eggs. [218, 221] Birds could potentially act as an additional
133
mechanism.[211, 212] Pig-pig transmission may play a role too, as susceptible pigs in contact with pigs experimentally fed with T. solium proglottids can develop viable infection, at least under controlled settings and if in close contact. [220] It is unclear, however, if any of these mechanisms could account for a sizable fraction of all infections. Nearly all attempts to recover T. solium eggs from soil and water near the residence and stool disposal of tapeworm carriers have been negative.[182, 184, 187, 209] This suggests that dispersion, if and when it occurs, does not lead to substantial environmental contamination and may not contribute substantially to infection rates.
VI.2. LIMITATIONS
One of the most important limitations of this research is the relatively small number of tapeworm carriers detected. Even in hyperendemic settings, the prevalence of taeniasis ranges between 0.3% and 6.0%[178, 179] and detection is further limited by the coverage of stool sample collection. The small number of tapeworm carriers detected limits the sources of variability and therefore our ability to detect differences. Additionally, for the study conducted in Matapalo (Chapters 3 and 4), Taenia eggs were detected by microscopy,[237] a technique that has 50% sensitivity[38] mainly due to the erratic egg excretion of T. solium tapeworms. [29] Undetected tapeworm carriers may have introduced misclassification when assessing the distance to the nearest tapeworm carrier, and some animals and humans were probably closer to carriers than our estimations. A more accurate identification of T. solium tapeworms may explain the
134
presence of high seropositivity hotspots without detected carriers nearby that lead to unexplained variability and poor fit in spline regression models.
The shape of the cysticercosis gradients surrounding carriers suggested an exponential increase in cysticercosis rates closer to carriers, but various factors limited the precision of such assessments. The few carriers detected, for example, were insufficient to accurately describe the cysticercosis gradient very close to carriers, partially because most households are far from each other in these semi-rural settings. Also, the number of households and herds was relatively small and did not provide sufficient data points to generate more precise estimates within each distance range.
A potential source of exposure misclassification in the Matapalo study was the lack of confirmation of Taenia species. Tapeworm carriers were detected by microscopy, but species identification was not achieved because the eggs of T. solium and T. saginata are visually indistinguishable and tapeworm segments were not found. As T. saginata is uncommon in the study area,[271] all tapeworms were considered T. solium. Therefore, it is possible that a few carriers had T. saginata tapeworms instead, and if so the distance to T. solium tapeworm carriers may be overestimated in some households and herds. However, it is unlikely that this type of misclassification was differential with regard to human and swine seropositivity. No apparent reason exists why microscopy would misclassify carriers differently in areas with higher or lower cysticercosis seropositivity. The impact of misclassification, thus, at most would be an attenuation of the strength of association between the distance to the carrier and cysticercosis seropositivity. The
135
clustering of seropositivity around carriers and the seropositivity gradient around them could actually be sharper than our estimations.
The test used to assess seropositivity is another important limitation of our research. The immunoblot assay, although highly sensitive and specific,[54, 55] assesses the presence of antibodies instead of infection status. However, the iceberg structure of human and swine cysticercosis shows that most exposure opportunities do not lead to establishment of infection but leave a detectable antibody response.[152] Often, antibody reactions are only transient and will disappear within a year,[57, 95] remaining unclear how they relate to immunity against future exposure. Additionally, piglets of infected mothers can remain seropositive for several months due to the persistence of maternal antibodies transmitted by colostrum.[94] Increased seropositivity near carriers, therefore, does not necessarily represent clusters of established infection, but instead could reflect clusters of continuously exposed individuals with a highly active antibody response but without infection. The presence of clusters of necropsy-confirmed swine infection around carriers, however, confirms that cysticercosis risk is substantially increased around carriers.
Our assessment of clustering in symptomatic neurocysticercosis surrounding carriers could be affected by outcome misclassification, as we relied on seizures cases as a marker of symptomatic neurocysticercosis. However, only 70% to 85% of all cases with symptomatic neurocysticercosis present with seizures.[108] Additionally, seizure cases could have been missed as a result of the incomplete coverage of the neurological
136
survey and imaging assessments or unreported seizures attacks due to the stigma associated with the condition. Therefore, some cases of symptomatic cysticercosis may be misclassified as non-cases, reducing the statistical power of the study and theoretically preventing the detection of a true association between symptomatic disease and distance to the carrier.
A limitation of the necropsy procedure was that the viability of apparently healthy, excised cysts was not evaluated beyond visual inspection. However, the sharper gradient of healthy cysts surrounding carriers compared to the gradient of degenerated cysts suggests that visual classification of viability was fairly accurate.
The information collected in the socioeconomic surveys could have improved the analysis by incorporating potential risk factors identified in previous epidemiological studies of cysticercosis transmission. A key variable was if pigs were raised free ranging, tied-up or in pens, to assess the benefits of different farming styles after controlling the effect of the distance to infection foci. Also, asking about a history of passing proglottids would have helped to evaluate if there was cysticercosis clustering around possible former carriers. Finally, two other indirect hygiene markers to consider in the future are the participants' education level and the materials of the households' floors and walls.
137
VI.3. DIRECTIONS OF FUTURE RESEARCH
VI.3.1 Define the appropriate radius of the intervention target zone. Evidence from this study supports expert opinions about the potential value of targeted control interventions applied to areas where a tapeworm carrier is detected. [10, 224, 263, 264] Our results, however, have not conclusively determined what should be the radius of the intervention area. Necropsy data showed that 94% of all cases of viable swine infection were found within 500m of a carrier, but the necropsy study was conducted in a highly rural area compared to Matapalo. The proportion of pigs living within 500m of a carrier in Matapalo were twice as high than in the necropsy study, and this factor may affect both the feasibility as well as the effectiveness of potential interventions. Also, further estimation of the shape of swine cysticercosis gradients around carriers in other settings should help to determine what the intervention radius should be.
VI.3.2 Revisit the intervention package and its delivery. The reductions in swine cysticercosis rates achieved by current cysticercosis control interventions are not satisfactory, and their sustainability has not been demonstrated. Combined chemotherapy, the most attractive option until a few years ago, [229] has not been able to attain and sustain low seropositivity in pigs in intervened areas, and the reasons for its limited effectiveness remain unclear. Treatment failure could be a factor, [201] as niclosamide cure rates of only 72% have been recently reported.[131] Additionally, simulation models of the effectiveness of control interventions have suggested that mass treatment coverage below 90% may not be sufficient to lead to elimination. [272] Reintroduction of disease
138
could be another factor. Vaccination currently appears as a promising alternative with high efficacy in controlled settings,[125, 232] but field trials have not been conducted yet. Additionally, vaccine delivery in field conditions may suffer from the same difficulties as the delivery of chemotherapy or other alternative control strategies.
VI.3.3 Improve diagnostic tools for porcine cysticercosis infection. The EITB test only detects antibodies and has limited specificity to detect infection or monitor the effectiveness of interventions. [201] Carcass examination is unfeasible in resource-limited settings,[10, 27, 83] and tongue examination has poor sensitivity in pigs with low burden infections,[66, 83, 84] which may be common after control interventions. An antigen detection urine test to assess viable infection in humans has been developed[273] and is currently being tested in field conditions. No similar tests exist for swine cysticercosis, however, limiting our ability to diagnose swine infection, conduct surveillance and evaluate intervention effectiveness.
VI.3.4 Enhance our understanding of transmission mechanisms. Despite the vast improvement in diagnostic, drugs and treatment for human and swine cysticercosis in the last 15 years, the understanding of transmission mechanisms has only improved marginally. Although the potential of flies and pigs to disseminate T. solium eggs is now better understood,[216, 220] it is still unknown whether these or other dispersion mechanisms play an important role in T. solium cysticercosis, and moreover, which mechanisms are important. Recent evidence has led to renewed interest about the role of dung beetles in T. solium egg dissemination (AE Gonzalez, non published observations), and future studies may help to elucidate this hypothesis.
139
REFERENCES
Commission on Tropical Diseases of the International League Against Epilepsy. Relationship between epilepsy and tropical diseases. Commission on Tropical Diseases of the International League Against Epilepsy. Epilepsia, 1994. 35(1):8993. Garcia HH, Gilman R, Martinez M, Tsang VC, Pilcher JB, Herrera G, Diaz F, Alvarado M, and Miranda E. Cysticercosis as a major cause of epilepsy in Peru. The Cysticercosis Working Group in Peru (CWG). Lancet, 1993. 341(8839): 197200. Medina MT, Rosas E, Rubio-Donnadieu F, and Sotelo J. Neurocysticercosis as the main cause of late-onset epilepsy in Mexico. Arch Intern Med, 1990. 150(2):325-7. Dixon HB, Lipscomb, FM., Cysticercosis: an Analysis and Follow-up of 450 cases. Special Report Series, ed. HMsS Office. Vol. 299. 1961, London: Medical Research Council. Schenone H, Epidemiology of human cysticercosis in LatinAmerica, in Cysticercosis: Present State of Knowledge and Perspectives, A Flisser, Willms, K., Laclette, J.P., Larralde, C , Ridaura, C , Beltran, F., Editor. 1982, Academic Press: New York. 25-38. White AC, Jr. Neurocysticercosis: a major cause of neurological disease worldwide. Clin Infect Dis, 1997. 24(2):101-13; quiz 114-5. Marconi VC, Garcia HH, and Katz JT. Neurocysticercosis. Curr Infect Dis Rep, 2006. 8(4):293-300. Schantz PM, Moore AC, Munoz JL, Hartman BJ, Schaefer JA, Aron AM, Persaud D, Sarti E, Wilson M, and Flisser A. Neurocysticercosis in an Orthodox Jewish community in New York City. N Engl J Med, 1992. 327(10):692-5. Tsang V and Wilson M. Taenia solium cysticercosis, an under-recognized but serious public health problem. Parasitol Today, 1995(11):124-126. Willingham AL, 3rd and Engels D. Control of Taenia solium cysticercosis/taeniosis. Adv Parasitol, 2006. 61:509-66. Nash TE and Neva FA. Recent advances in the diagnosis and treatment of cerebral cysticercosis. N Engl J Med, 1984. 311(23): 1492-6. Garcia HH and Del Brutto OH. Taenia solium cysticercosis. Infect Dis Clin North Am, 2000. 14(1):97-119. Allan JC, Velasquez-Tohom M, Garcia-Noval J, Torres-Alvarez R, Yurrita P, Fletes C, de Mata F, Soto de Alfaro H, and Craig PS. Epidemiology of intestinal taeniasis in four, rural, Guatemalan communities. Ann Trop Med Parasitol, 1996. 90(2): 157-65. Garcia HH, Gilman RH, Gonzalez AE, Verastegui M, Rodriguez S, Gavidia C, Tsang VC, Falcon N, Lescano AG, Moulton LH, Bernal T, and Tovar M. Hyperendemic human and porcine Taenia solium infection in Peru. Am J Trop Med Hyg, 2003. 68(3):268-75.
140
15.
16.
17. 18. 19. 20.
21.
22.
23.
24.
25.
26. 27. 28.
29. 30. 31.
Gemmell MA and Johnstone PD. Factors regulating tapeworm populations: dispersion of eggs of Taenia hydatigena on pasture. Ann Trop Med Parasitol, 1976. 70(4):431-4. Gemmell MA, Johnstone PD, and Boswell CC. Factors regulating tapeworm populations: dispersion patterns of Taenia hydatigena eggs on pasture. Res Vet Sci, 1978. 24(3):334-8. Cooper J, Gordon IJ, and Pike AW. Strategies for the avoidance of faeces by grazing sheep. Appl Anim Behav Sci, 2000. 69(1): 15-33. Gleed PT and Sansom BF. Ingestion of iron in sow's faeces by piglets reared in farrowing crates with slottedfloors. Br J Nutr, 1982. 47(1):113-7. Sansom BF and Gleed PT. The ingestion of sow's faeces by suckling piglets. Br J Nutr, 1981. 46(3):451-6. Henneberg R, Die tierischen parasiten des zentralnervensystem, in Handbuch der neurologie, M Lewandowsky, Editor. 1912, Verlag Von Julius Springer: Berlin. 643-712. Flisser A, Correa D, Avila G, and Maravilla P, Biology of Taenia Solium, Taenia Saginata and Taenia Saginata Asiatica, in WHO/FAO/OIE Guidelines for the Surveillance, Prevention and Control ofTaeniasis/Cysticercosis, KD Murrell, Editor. 2005: Geneva, Switzerland. 1-10. de Aluja AS, Martinez MJ, and Villalobos AN. Taenia solium cysticercosis in young pigs: age at first infection and histological characteristics. Vet Parasitol, 1998. 76(l-2):71-9. Yoshino K. Studies on the post-embryonal development of Taenia solium: III. On the development of Cysticercus cellulosae within the definitive intermediate host. J Med Assoc Formosa, 1933. 32:166-169. Gemmell M, Matyas, Z., Pawlowsky, Z., Soulsby, E.J.L., Guidelines for surveillance and control of Taeniasis/Cysticercosis. VPH. Vol. 83.49. 1983, Geneva: World Health Organization. 207. Willingham AL, 3rd, De NV, Doanh NQ, Cong le D, Dung TV, Dorny P, Cam PD, and Dalsgaard A. Current status of cysticercosis in Vietnam. Southeast Asian J Trop Med Public Health, 2003. 34 Suppl 1:35-50. Pawlowski Z and Schultz MG. Taeniasis and cysticercosis (Taenia saginata). Adv Parasitol, 1972. 10:269-343. Garcia HH, Gonzalez AE, Evans CAW, Gilman RH, and The Cysticercosis Working Group in Peru. Taenia solium cysticercosis. Lancet, 2003. 362:547-56. Garcia HH, Gilman RH, Tsang VC, and Gonzalez AE. Clinical significance of neurocysticercosis in endemic villages. The Cysticercosis Working Group in Peru. Trans R Soc Trop Med Hyg, 1997. 91(2):176-8. Schantz PM and Sarti-Gutierrez E. Diagnostic methods and epidemiologic surveillance of Taenia solium infection. Acta Leiden, 1989. 57(2): 153-63. Richards F, Jr. and Schantz PM. Cysticercosis and taeniasis. N Engl J Med, 1985. 312(12):787-8. Hall A, Latham MC, Crompton DW, and Stephenson LS. Taenia saginata (Cestoda) in western Kenya: the reliability of faecal examinations in diagnosis. Parasitology, 1981. 83:91-101.
141
32. 33.
34.
35.
36. 37. 38.
39.
40.
41. 42.
43.
44.
45.
de Kaminsky RG. Albendazole treatment in human taeniasis. Trans R Soc Trop MedHyg, 1991. 85(5):648-50. Schantz PM, Wilkins PP, and Tsang VCW, Immigrants, imaging and immunoblots: the emergence ofneurocysticercosis as a significant public health problem, in Emerging Infections 2, WM Scheld, WA Craig, and JM Hughes, Editors. 1998, ASM Press: Washington. 213-241. Mayta H, Talley A, Gilman RH, Jimenez J, Verastegui M, Ruiz M, Garcia HH, and Gonzalez AE. Differentiating Taenia solium and Taenia saginata infections by simple hematoxylin-eosin staining and PCR-restriction enzyme analysis. J Clin Microbiol, 2000. 38(1): 133-7. Jeri C, Gilman RH, Lescano AG, Mayta H, Ramirez ME, Gonzalez AE, Nazerali R, and Garcia HH. Species identification after treatment for human taeniasis. Lancet, 2004. 363(9413):949-50. Verster A. Redescription of Taenia solium Linnaeus, 1758 and Taenia saginata Goeze, 1782. Z Parasitenkd, 1967. 29(4):313-28. Allan JC, Avila G, Garcia Noval J, Flisser A, and Craig PS. Immunodiagnosis of taeniasis by coproantigen detection. Parasitology, 1990. 101 Pt 3:473-7. Allan JC, Velasquez-Tohom M, Torres-Alvarez R, Yurrita P, and Garcia-Noval J. Field trial of the coproantigen-based diagnosis of Taenia solium taeniasis by enzyme-linked immunosorbent assay. Am J Trop Med Hyg, 1996. 54(4):352-6. Yamasaki H, Allan JC, Sato MO, Nakao M, Sako Y, Nakaya K, Qiu D, Mamuti W, Craig PS, and Ito A. DNA differential diagnosis of taeniasis and cysticercosis by multiplex PCR. J Clin Microbiol, 2004. 42(2):548-53. Allan JC, Mencos F, Garcia-Noval J, Sarti E, Flisser A, Wang Y, Liu D, and Craig PS. Dipstick dot ELISAfor the detection of Taenia coproantigens in humans. Parasitology, 1993. 107(Pt l):79-85. Allan JC and Craig PS. Coproantigens in taeniasis and echinococcosis. Parasitol Int, 2006. 55 Suppl:S75-80. Gonzalez LM, Montero E, Sciutto E, Harrison LJ, Parkhouse RM, and Garate T. Differential diagnosis of Taenia saginata and Taenia solium infections: from DNA probes to polymerase chain reaction. Trans R Soc Trop Med Hyg, 2002. 96 Suppll:S243-50. Rodriguez-Hidalgo R, Geysen D, Benitez-Ortiz W, Geerts S, and Brandt J. Comparison of conventional techniques to differentiate between Taenia solium and Taenia saginata and an improved polymerase chain reaction-restriction fragment length polymorphism assay using a mitochondrial 12S rDNA fragment. J Parasitol, 2002. 88(5):1007-11. Gonzalez LM, Montero E, Harrison LJ, Parkhouse RM, and Garate T. Differential diagnosis of Taenia saginata and Taenia solium infection by PCR. J Clin Microbiol, 2000. 38(2):737-44. Gonzalez LM, Montero E, Puente S, Lopez-Velez R, Hernandez M, Sciutto E, Harrison LJ, Parkhouse RM, and Garate T. PCR tools for the differential diagnosis of Taenia saginata and Taenia solium taeniasis/cysticercosis from different geographical locations. Diagn Microbiol Infect Dis, 2002. 42(4):243-9.
142
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
Wilkins PP, Allan JC, Verastegui M, Acosta M, Eason AG, Garcia HH, Gonzalez AE, Gilman RH, and Tsang VC. Development of a serologic assay to detect Taenia solium taeniasis. Am J Trop Med Hyg, 1999. 60(2): 199-204. DeGiorgio C, Pietsch-Escueta S, Tsang V, Corral-Leyva G, Ng L, Medina MT, Astudillo S, Padilla N, Leyva P, Martinez L, Noh J, Levine M, del Villasenor R, and Sorvillo F. Sero-prevalence of Taenia solium cysticercosis and Taenia solium taeniasis in California, USA. Acta Neurol Scand, 2005. lll(2):84-8. Levine MZ, Calderon JC, Wilkins PP, Lane WS, Asara JM, Hancock K, Gonzalez AE, Garcia HH, Gilman RH, and Tsang VC. Characterization, cloning, and expression of two diagnostic antigens for Taenia solium tapeworm infection. J Parasitol, 2004. 90(3):631-8. Levine MZ, Lewis MM, Jimenez JA, Rodrigues S, Khan A, Garcia HH, Gonzalez AE, Gilman RH, and Tsang VCW. Development an enzyme-linked immunoelectrotransfer blot (EITB) assay using two baculovirus expressed recombinant antigens for diagnosis of taenia solium taeniasis. J Parasitol, 2007. 93(2):409-417. Garcia HH, Del Brutto OH, Nash TE, White AC, Jr., Tsang VC, and Gilman RH. New concepts in the diagnosis and management of neurocysticercosis (Taenia solium). Am J Trop Med Hyg, 2005. 72(l):3-9. Garcia HH, Gonzalez AE, Tsang VCW, Gilman RH, and For The Cysticercosis Working Group in Peru. Neurocysticercosis: some of the essentials. Practical Neurology, 2006. 6:206-14. Del Brutto OH, Wadia NH, Dumas M, Cruz M, Tsang VC, and Schantz PM. Proposal of diagnostic criteria for human cysticercosis and neurocysticercosis. J Neurol Sci, 1996. 142(l-2):l-6. Del Brutto OH, Rajshekhar V, White AC, Jr., Tsang VC, Nash TE, Takayanagui OM, Schantz PM, Evans CA, Flisser A, Correa D, Botero D, Allan JC, Sarti E, Gonzalez AE, Gilman RH, and Garcia HH. Proposed diagnostic criteria for neurocysticercosis. Neurology, 2001. 57(2):177-83. Tsang VC, Brand JA, and Boyer AE. An enzyme-linked immunoelectrotransfer blot assay and glycoprotein antigens for diagnosing human cysticercosis (Taenia solium). J Infect Dis, 1989. 159(l):50-9. Tsang VC, Pilcher JA, Zhou W, Boyer AE, Kamango-Sollo EI, Rhoads ML, Murrell KD, Schantz PM, and Gilman RH. Efficacy of the immunoblot assay for cysticercosis in pigs and modulated expression of distinct IgM/IgG activities to Taenia solium antigens in experimental infections. Vet Immunol Immunopathol, 1991.29(l-2):69-78. Wilson M, Bryan RT, Fried JA, Ware DA, Schantz PM, Pilcher JB, and Tsang VC. Clinical evaluation of the cysticercosis enzyme-linked immunoelectrotransfer blot in patients with neurocysticercosis. J Infect Dis, 1991. 164(5): 1007-9. Garcia HH, Gonzalez AE, Gilman RH, Palacios LG, Jimenez I, Rodriguez S, Verastegui M, Wilkins P, and Tsang VC. Short report: transient antibody response in Taenia solium infection infield conditions-a major contributor to high seroprevalence. Am J Trop Med Hyg, 2001. 65(l):31-2.
143
58.
59.
60.
61.
62.
63.
64.
65. 66.
67. 68.
69.
70.
Garcia HH, Gilman RH, Catacora M, Verastegui M, Gonzalez AE, and Tsang VC. Serologic evolution of neurocysticercosis patients after antiparasitic therapy. Cysticercosis Working Group in Peru. J Infect Dis, 1997. 175(2):486-9. Garcia-Noval J, Allan JC, Fletes C, Moreno E, DeMata F, Torres-Alvarez R, Soto de Alfaro H, Yurrita P, Higueros-Morales H, Mencos F, and Craig PS. Epidemiology of Taenia solium taeniasis and cysticercosis in two rural Guatemalan communities. Am J Trop Med Hyg, 1996. 55(3):282-9. Subahar R, Hamid A, Purba W, Wandra T, Karma C, Sako Y, Margono SS, Craig PS, and Ito A. Taenia solium infection in Irian Jaya (west Papua), Indonesia: a pilot serological survey of human and porcine cysticercosis in Jayawijaya district. Trans R Soc Trop Med Hyg, 2001. 95(4):388-90. Proano-Narvaez JV, Meza-Lucas A, Mata-Ruiz O, Garcia-Jeronimo RC, and Correa D. Laboratory diagnosis of human neurocysticercosis: double-blind comparison of enzyme-linked immunosorbent assay and electroimmunotransfer blot assay. J Clin Microbiol, 2002. 40(6):2115-8. Gekeler F, Eichenlaub S, Mendoza EG, Sotelo J, Hoelscher M, and Loscher T. Sensitivity and specificity ofELISA and immunoblot for diagnosing neurocysticercosis. Eur J Clin Microbiol Infect Dis, 2002. 21(3):227-9. Baily GG, Mason PR, Trijssenar FE, and Lyons NF. Serological diagnosis of neurocysticercosis: evaluation ofELISA tests using cyst fluid and other components of Taenia solium cysticerci as antigens. Trans R Soc Trop Med Hyg, 1988. 82(2):295-9. Diwan AR, Coker-Vann M, Brown P, Subianto DB, Yolken R, Desowitz R, Escobar A, Gibbs CJ, Jr., and Gajdusek DC. Enzyme-linked immunosorbent assay (ELISA)for the detection of antibody to cysticerci of Taenia solium. Am J Trop Med Hyg, 1982. 31(2):364-9. Sako Y and Ito A. Recent advances in serodiagnosis for cysticercosis. Southeast Asian J Trop Med Public Health, 2001. 32 Suppl 2:98-104. Sato MO, Yamasaki H, Sako Y, Nakao M, Nakaya K, Plancarte A, Kassuku AA, Dorny P, Geerts S, Benitez-Ortiz W, Hashiguchi Y, and Ito A. Evaluation of tongue inspection and serology for diagnosis of Taenia solium cysticercosis in swine: usefulness ofELISA using purified glycoproteins and recombinant antigen. Vet Parasitol, 2003. 111(4):309-22. Dorny P, Brandt J, Zoli A, and Geerts S. Immunodiagnostic tools for human and porcine cysticercosis. Acta Trop, 2003. 87(l):79-86. Garcia HH, Parkhouse RM, Gilman RH, Montenegro T, Bernal T, Martinez SM, Gonzalez AE, Tsang VC, and Harrison LJ. Serum antigen detection in the diagnosis, treatment, andfollow-up of neurocysticercosis patients. Trans R Soc Trop Med Hyg, 2000. 94(6):673-6. Correa D, Sandoval MA, Harrison LJ, Parkhouse RM, Plancarte A, Meza-Lucas A, and Flisser A. Human neurocysticercosis: comparison of enzyme immunoassay capture techniques based on monoclonal and polyclonal antibodies for the detection of parasite products in cerebrospinal fluid. Trans R Soc Trop Med Hyg, 1989. 83(6):814-6. Garcia HH, Harrison LJ, Parkhouse RM, Montenegro T, Martinez SM, Tsang VC, and Gilman RH. A specific antigen-detection ELISAfor the diagnosis of human
144
71. 72.
73.
74.
75.
76. 77.
78.
79.
80.
81. 82.
83.
84.
neurocysticercosis. The Cysticercosis Working Group in Peru. Trans R Soc Trop Med Hyg, 1998. 92(4):411-4. Garcia HH and Del Brutto OH. Imaging findings in neurocysticercosis. Acta Tropica, 2003. 87:71-78. Garcia HH, Gonzalez AE, Gilman RH, and for The Cysticercosis Working Group in Peru. Diagnosis, treatment and control of Taenia solium cysticercosis. Curr Opin Inf Dis, 2003(16):411-419. Escobar A, The pathology of neurocysticercosis, in Cysticercosis of the central nervous system, E Palacios, J Rodriguez-Carbajal, and JM Taveras, Editors. 1983, Charles C. Thomas: Springfield. 27-54. Rajshekhar V, Wilson M, and Schantz PM. Cysticercus immunoblot assay in Indian patients with single small enhancing CT lesions. J Neurol Neurosurg Psychiatry, 1991. 54(6):561-2. Carbajal JR, Palacios E, Azar-Kia B, and Churchill R. Radiology of cysticercosis of the central nervous system including computed tomography. Radiology, 1977. 125(1):127-31. Bentson JR, Wilson GH, Helmer E, and Winter J. Computed tomography in intracranial cysticercosis. J Comput Assist Tomogr, 1977. 1(4):464-71. Sotelo J, Guerrero V, and Rubio F. Neurocysticercosis: a new classification based on active and inactive forms. A study of 753 cases. Arch Intern Med, 1985. 145(3):442-5. Garcia HH, Evans CA, Nash TE, Takayanagui OM, White AC, Jr., Botero D, Rajshekhar V, Tsang VC, Schantz PM, Allan JC, Flisser A, Correa D, Sarti E, Friedland JS, Martinez SM, Gonzalez AE, Gilman RH, and Del Brutto OH. Current consensus guidelines for treatment of neurocysticercosis. Clin Microbiol Rev, 2002. 15(4):747-56. Garcia HH, Herrera G, Gilman RH, Tsang VC, Pilcher JB, Diaz JF, Candy EJ, Miranda E, and Naranjo J. Discrepancies between cerebral computed tomography and western blot in the diagnosis of neurocysticercosis. The Cysticercosis Working Group in Peru (Clinical Studies Coordination Board). Am J Trop Med Hyg, 1994. 50(2): 152-7. Martinez HR, Rangel-Guerra R, Elizondo G, Gonzalez J, Todd LE, Ancer J, and Prakash SS. MR imaging in neurocysticercosis: a study of 56 cases. AJNR Am J Neuroradiol, 1989. 10(5):1011-9. Dumas JL, Vusy JM, and Belin C. Parenchymal neurocysticercosis: follow up and staging by MRI. Neuroradiology, 1997. 39:12-16. Suss RA, Maravilla KR, and Thompson J. MR imaging of intracranial cysticercosis: comparison with CT and anatomopathologic features. AJNR Am J Neuroradiol, 1986. 7(2):235-42. Gonzalez AE, Cama V, Gilman RH, Tsang VC, Pilcher JB, Chavera A, Castro M, Montenegro T, Verastegui M, Miranda E, and Bazalar H. Prevalence and comparison of serologic assays, necropsy, and tongue examination for the diagnosis of porcine cysticercosis in Peru. Am J Trop Med Hyg, 1990. 43(2): 1949. Sciutto E, Martinez JJ, Villalobos NM, Hernandez M, Jose MV, Beltran C, Rodarte F, Flores I, Bobadilla JR, Fragoso G, Parkhouse ME, Harrison LJ, and de
145
85.
86.
87.
88.
89.
90.
91. 92. 93. 94.
95.
96.
97. 98. 99. 100.
Aluja AS. Limitations of current diagnostic procedures for the diagnosis of Taenia solium cysticercosis in rural pigs. Vet Parasitol, 1998. 79(4):299-313. Nguekam A, Zoli AP, Vondou L, Pouedet SM, Assana E, Domy P, Brandt J, Losson B, and Geerts S. Kinetics of circulating antigens in pigs experimentally infected with Taenia solium eggs. Vet Parasitol, 2003. 111(4):323-32. Phiri IK, Domy P, Gabriel S, Willingham AL, 3rd, Speybroeck N, and Vercruysse J. The prevalence of porcine cysticercosis in Eastern and Southern provinces of Zambia. Vet Parasitol, 2002. 108(l):31-9. Pouedet MS, Zoli AP, Nguekam, Vondou L, Assana E, Speybroeck N, Berkvens D, Dorny P, Brandt J, and Geerts S. Epidemiological survey of swine cysticercosis in two rural communities of West-Cameroon. Vet Parasitol, 2002. 106(l):45-54. Sarti Gutierrez E, Schantz PM, Aguilera J, and Lopez A. Epidemiologic observations on porcine cysticercosis in a rural community ofMichoacan State, Mexico. Vet Parasitol, 1992. 41(3-4):195-201. Sarti-Gutierrez EJ, Schantz PM, Lara-Aguilera R, Gomez Dandoy H, and Flisser A. Taenia solium taeniasis and cysticercosis in a Mexican village. Trop Med Parasitol, 1988. 39(3): 194-8. Dorny P, Detection and Diagnosis, in WHO/FAO/OIE Guidelines for the Surveillance, Prevention and Control ofTaeniasis/Cysticercosis, KD Murrell, Editor. 2005: Geneva, Switzerland. 45-55. The Cysticercosis Working Group in Peru. The marketing of cysticercotic pigs in the Sierra of Peru. Bull World Health Organ, 1993. 71(2):223-8. Escalante S. [Epidemiology of cysticercosis in Peru]. Rev Neuropsiquiatr, 1977. 40(l):29-39. Inope L, Rojas M, and Bullon F. [Cysticercosis in Peru. Various statistical aspects]. Rev Neuropsiquiatr, 1977. 40(l):40-52. Gonzalez AE, Verastegui M, Noh JC, Gavidia C, Falcon N, Bernal T, Garcia HH, Tsang VC, Gilman RH, and Wilkins PP. Persistence of passively transferred antibodies in porcine Taenia solium cysticercosis. Cysticercosis Working Group in Peru. Vet Parasitol, 1999. 86(2):113-8. Garcia HH, Gonzalez AE, Gavidia C, Falcon N, Bernal T, Verastegui M, Rodriguez S, Tsang VC, and Gilman RH. Seroincidence of porcine T. solium infection in the Peruvian highlands. Prev Vet Med, 2003. 57(4):227-36. Dorny P, Phiri IK, Vercruysse J, Gabriel S, Willingham AL, 3rd, Brandt J, Victor B, Speybroeck N, and Berkvens D. A Bayesian approach for estimating values for prevalence and diagnostic test characteristics of porcine cysticercosis. Int J Parasitol, 2004. 34(5):569-76. Botero D, Tanowitz HB, Weiss LM, and Wittner M. Taeniasis and cysticercosis. Infect Dis Clin North Am, 1993. 7(3):683-97. Flisser A. Taeniasis and cysticercosis due to Taenia solium. Prog Clin Parasitol, 1994.4:77-116. Bia FJ and Barry M. Parasitic infections of the central nervous system. Neurol Clin, 1986. 4(l):171-206. Sotelo J, del Brutto OH, Penagos P, Escobedo F, Torres B, Rodriguez-Carbajal J, and Rubio-Donnadieu F. Comparison of therapeutic regimen of anticysticercal drugs for parenchymal brain cysticercosis. J Neurol, 1990. 237(2):69-72.
146
101.
102.
103.
104.
105.
106.
107. 108.
109. 110.
111. 112.
113. 114.
115. 116.
Nash TE, Del Brutto OH, Butman JA, Corona T, Delgado-Escueta A, Duron RM, Evans CA, Gilman RH, Gonzalez AE, Loeb JA, Medina MT, Pietsch-Escueta S, Pretell EJ, Takayanagui OM, Theodore W, Tsang VC, and Garcia HH. Calcific neurocysticercosis and epileptogenesis. Neurology, 2004. 62(11):1934-8. Cruz ME, Schantz PM, Cruz I, Espinosa P, Preux PM, Cruz A, Benitez W, Tsang VC, Fermoso J, and Dumas M. Epilepsy and neurocysticercosis in an Andean community. Int J Epidemiol, 1999. 28(4):799-803. Sanchez AL, Lindback J, Schantz PM, Sone M, Sakai H, Medina MT, and Ljungstrom I. A population-based, case-control study of Taenia solium taeniasis and cysticercosis. Ann Trop Med Parasitol, 1999. 93(3):247-58. Garcia-Noval J, Moreno E, de Mata F, Soto de Alfaro H, Fletes C, Craig PS, and Allan JC. An epidemiological study of epilepsy and epileptic seizures in two rural Guatemalan communities. Ann Trop Med Parasitol, 2001. 95(2): 167-75. Del Brutto OH, Santibanez R, Idrovo L, Rodriguez S, Diaz-Calderon E, Navas C, Gilman RH, Cuesta F, Mosquera A, Gonzalez AE, Tsang VC, and Garcia HH. Epilepsy and neurocysticercosis in Atahualpa: a door-to-door survey in rural coastal Ecuador. Epilepsia, 2005. 46(4):583-7. Medina MT, Duron RM, Martinez L, Osorio JR, Estrada AL, Zuniga C, Cartagena D, Collins JS, and Holden KR. Prevalence, incidence, and etiology of epilepsies in rural Honduras: the Salama Study. Epilepsia, 2005. 46(1): 124-31. Garcia HH and Del Brutto OH. Neurocysticercosis: updated concepts about an old disease. Lancet Neurol, 2005. 4(10):653-61. Del Brutto OH, Santibanez R, Noboa CA, Aguirre R, Diaz E, and Alarcon TA. Epilepsy due to neurocysticercosis: analysis of 203 patients. Neurology, 1992. 42(2):389-92. Rajshekhar V and Abraham J. Disappearing CT lesions in Indian patients with epilepsy. J Neurol Neurosurg Psychiatry, 1990. 53(9):818-9. Chandy MJ, Rajshekhar V, Ghosh S, Prakash S, Joseph T, Abraham J, and Chandi SM. Single small enhancing CT lesions in Indian patients with epilepsy: clinical, radiological and pathological considerations. J Neurol Neurosurg Psychiatry, 1991. 54(8):702-5. Rangel R, Torres B, Del Bruto O, and Sotelo J. Cysticercotic encephalitis: a severe form in young females. Am J Trop Med Hyg, 1987. 36(2):387-92. Proano JV, Madrazo I, Avelar F, Lopez-Felix B, Diaz G, and Grijalva I. Medical treatment for neurocysticercosis characterized by giant subarachnoid cysts. N Engl J Med, 2001. 345(12):879-85. Bickerstaff ER, Cloake PCP, Hughes B, and Smith WT. The racemose form of cerebral cysticercosis. Brain, 1952. 75:1-16. Cuetter AC, Garcia-Bobadilla J, Guerra LG, Martinez FM, and Kaim B. Neurocysticercosis: focus on intraventricular disease. Clin Infect Dis, 1997. 24(2): 157-64. Rahalkar MD, Shetty DD, Kelkar AB, Kelkar AA, Kinare AS, and Ambardekar ST. The many faces of cysticercosis. Clin Radiol, 2000. 55(9):668-74. Pushker N, Bajaj MS, Chandra M, and Neena. Ocular and orbital cysticercosis. Acta Ophthalmol Scand, 2001. 79(4):408-13.
147
117. 118.
119. 120.
121.
122. 123.
124.
125.
126. 127.
128.
129. 130. 131.
Sawhney BB, Chopra JS, Banerji AK, and Wahi PL. Pseudohypertrophic myopathy in cysticerosis. Neurology, 1976. 26(3):270-2. Ito A, Yamasaki H, Nakao M, Sako Y, Okamoto M, Sato MO, Nakaya K, Margono SS, Ikejima T, Kassuku AA, Afonso SM, Ortiz WB, Plancarte A, Zoli A, Geerts S, and Craig PS. Multiple genotypes of Taenia solium—ramifications for diagnosis, treatment and control. ActaTrop, 2003. 87(1):95-101. Dixon HBF and Smithers DW. Epilepsy in cysticercosis (Taenia solium). A study of seventy-one cases. Quart J Med, 1934. 3:603-616. Costa-Cruz JM, Rocha A, Silva AM, De Moraes AT, Guimaraes AH, Salomao EC, and Alcantara TM. [Occurrence of cysticercosis in autopsies performed in Uberlandia, Minas Gerais, Brazil]. Arq Neuropsiquiatr, 1995. 53(2):227-32. Wadia N, Desai S, and Bhatt M. Disseminated cysticercosis. New observations, including CT scan findings and experience with treatment by praziquantel. Brain, 1988. lll(Pt3):597-614. Xu ZB. [Muscular pseudohypertrophy due to cysticercus: a report of 3 cases (author's transl)]. Zhonghua Nei Ke Za Zhi, 1979. 18(6):409-l 1. Rabiela MT, Rivas A, Rodriguez J, Castillo S, and Cancino FM, Anatomopathological aspects of human brain cysticercosis, in Cysticercosis: Present State of Knowledge and Perspectives, A Flisser, Willms, K., Laclette, J.P., Larralde, C , Ridaura, C , Beltran, F., Editor. 1982, Academic Press: New York. 179-200. Gonzales AE, Garcia HH, Gilman RH, Gavidia CM, Tsang VC, Bernal T, Falcon N, Romero M, and Lopez-Urbina MT. Effective, single-dose treatment or porcine cysticercosis with oxfendazole. Am J Trop Med Hyg, 1996. 54(4):391-4. Gonzalez AE, Gauci CG, Barber D, Gilman RH, Tsang VC, Garcia HH, Verastegui M, and Lightowlers MW. Vaccination of pigs to control human neurocysticercosis. Am J Trop Med Hyg, 2005. 72(6):837-9. Torres JR, Noya O, de Noya BA, and Mondolfi A. Seizures and praziquantel. A case report. Rev Inst Med Trop Sao Paulo, 1988. 30(6):433-6. Flisser A, Madrazo I, Plancarte A, Schantz P, Allan J, Craig P, and Sarti E. Neurological symptoms in occult neurocysticercosis after single taeniacidal dose of praziquantel. Lancet, 1993. 342(8873):748. Pawlowski ZS, Allan JC, and Meinardi H, Control Measures for Taeniosis and Cysticercosis, in WHO/FAO/OIE Guidelines for the Surveillance, Prevention and Control of Taeniasis/Cysticercosis, KD Murrell, Editor. 2005: Geneva, Switzerland. 73-99. Pearson RD and Hewlett EL. Niclosamide therapy for tapeworm infections. Ann Intern Med, 1985. 102(4):550-1. Richards F, Jr. and Schantz PM. Treatment of Taenia solium infections. Lancet, 1985. 1(8440): 1264-5. Bustos JA, Rodriguez S, Jimenez J, Lescano AG, Moyano L, Gonzalvez G, Allan JC, Gonzalez AE, Gilman RH, Tsang VCW, Garcia HH, and Peru fTCWGi. Coproantigen Detection for Early and Accurate Assessment ofTaeniasis Treatment, in 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene. 2005. Washington, DC.
148
132. 133.
134.
135.
136. 137.
138.
139.
140. 141.
142.
143.
144.
Del Brutto OH. Is the course of neurocysticercosis modified by treatment with anthelmintic agents? Arch Intern Med, 1997. 157(l):128-30. Nash TE, Singh G, White AC, Rajshekhar V, Loeb JA, Proano JV, Takayanagui OM, Gonzalez AE, Butman JA, DeGiorgio C, Del Brutto OH, Delgado-Escueta A, Evans CA, Gilman RH, Martinez SM, Medina MT, Pretell EJ, Teale J, and Garcia HH. Treatment of neurocysticercosis: current status andfuture research needs. Neurology, 2006. 67(7):1120-7. Garcia HH, Pretell EJ, Gilman RH, Martinez SM, Moulton LH, Del Brutto OH, Herrera G, Evans CA, and Gonzalez AE. A trial of antiparasitic treatment to reduce the rate of seizures due to cerebral cysticercosis. N Engl J Med, 2004. 350(3):249-58. Del Brutto OH, Roos KL, Coffey CS, and Garcia HH. Meta-analysis: Cysticidal drugs for neurocysticercosis: albendazole and praziquantel. Ann Intern Med, 2006. 145(1):43-51. Corona T, Lugo R, Medina R, and Sotelo J. Single-day praziquantel therapy for neurocysticercosis. N Engl J Med, 1996. 334(2):125. Bandres JC, White AC, Jr., Samo T, Murphy EC, and Harris RL. Extraparenchymal neurocysticercosis: report of five cases and review of management. Clin Infect Dis, 1992. 15(5):799-811. Del Brutto OH. Albendazole therapy for subarachnoid cysticerci: clinical and neuroimaging analysis of 17patients. J Neurol Neurosurg Psychiatry, 1997. 62(6):659-61. Anandh B, Mohanty A, Sampath S, Praharaj SS, and Kolluri S. Endoscopic approach to intraventricular cysticercal lesions. Minim Invasive Neurosurg, 2001. 44(4): 194-6. Bergsneider M. Endoscopic removal of cysticercal cysts within the fourth ventricle. Technical note. J Neurosurg, 1999. 91(2):340-5. Bergsneider M, Holly LT, Lee JH, King WA, and Frazee JG. Endoscopic management of cysticercal cysts within the lateral and third ventricles. J Neurosurg, 2000. 92(l):14-23. Flisser A, Gonzalez D, Plancarte A, Ostrosky P, Montero R, Stephano A, and Correa D. Praziquantel treatment of brain and muscle porcine Taenia solium cysticercosis. 2. Immunological and cytogenetic studies. Parasitol Res, 1990. 76(7):640-2. Torres A, Plancarte A, Villalobos AN, de Aluja AS, Navarro R, and Flisser A. Praziquantel treatment of porcine brain and muscle Taenia solium cysticercosis. 3. Effect of 1-day treatment. Parasitol Res, 1992. 78(2): 161-4. Kaur M, Joshi K, Ganguly NK, Mahajan RC, and Malla N. Evaluation of the efficacy of albendazole against the larvae of Taenia solium in experimentally infected pigs, and kinetics of the immune response. Int J Parasitol, 1995.
145.
25(12): 1443-50. Gonzalez AE, Garcia HH, Gilman RH, Lopez MT, Gavidia C, McDonald J, Pilcher JB, and Tsang VC. Treatment of porcine cysticercosis with albendazole. Am J Trop Med Hyg, 1995. 53(5):571-4.
149
146.
147.
148.
149.
150.
151.
152.
153. 154.
155.
156. 157. 158. 159. 160.
161.
Peniche-Cardena A, Dominguez-Alpizar JL, Sima-Alvarez R, Argaez-Rodriguez F, Fraser A, Craig PS, and Rodriguez-Canul R. Chemotherapy of porcine cysticercosis with albendazole sulphoxide. Vet Parasitol, 2002. 108(l):63-73. Gonzalez AE, Falcon N, Gavidia C, Garcia HH, Tsang VC, Bernal T, Romero M, and Gilman RH. Treatment of porcine cysticercosis with oxfendazole: a doseresponse trial. VetRec, 1997. 141(16):420-2. Gonzalez AE, Falcon N, Gavidia C, Garcia HH, Tsang VC, Bernal T, Romero M, and Gilman RH. Time-response curve of oxfendazole in the treatment of swine cysticercosis. Am J Trop Med Hyg, 1998. 59(5):832-6. Gonzalez AE, Gavidia C, Falcon N, Bernal T, Verastegui M, Garcia HH, Gilman RH, and Tsang VC. Protection of pigs with cysticercosis from further infections after treatment with oxfendazole. Am J Trop Med Hyg, 2001. 65(l):15-8. Jung H, Hurtado M, Sanchez M, Medina MT, and Sotelo J. Plasma and CSF levels of albendazole and praziquantel in patients with neurocysticercosis. Clin Neuropharmacol, 1990. 13(6):559-64. Roman G, Sotelo J, Del Brutto O, Flisser A, Dumas M, Wadia N, Botero D, Cruz M, Garcia H, de Bittencourt PR, Trelles L, Arriagada C, Lorenzana P, Nash TE, and Spina-Franca A. A proposal to declare neurocysticercosis an international reportable disease. Bull World Health Organ, 2000. 78(3):399-406. Bern C, Garcia HH, Evans C, Gonzalez AE, Verastegui M, Tsang VC, and Gilman RH. Magnitude of the disease burden from neurocysticercosis in a developing country. Clin Infect Dis, 1999. 29(5):1203-9. Wallin MT and Kurtzke JF. Neurocysticercosis in the United States: review of an important emerging infection. Neurology, 2004. 63(9): 1559-64. Shandera WX, White AC, Jr., Chen JC, Diaz P, and Armstrong R. Neurocysticercosis in Houston, Texas. A report of 112 cases. Medicine (Baltimore), 1994. 73(l):37-52. Font Puig C, Ruiz Postigo JA, Munoz Batet C, Pardos Arnal F, and Corachan Cuyas M. [Neurocysticercosis in Spain. Apropos 4 cases seen in immigrant patients from endemic countries]. An Med Interna, 1999. 16(2):89-91. Dietrichs E, Tyssvang T, Aanonsen NO, and Bakke SJ. Cerebral cysticercosis in Norway. Acta Neurol Scand, 1993. 88(4):296-8. Rousseau MC, Guillotel B, and Delmont J. [Neurocysticercosis in the South-East of France 1988-1998]. Presse Med, 1999. 28(39):2141-4. Morgado C, Gomes LB, and de Campos JG. [Neurocysticercosis. An imaging analysis of 35 cases]. Acta Med Port, 1994. 7(5):269-75. Hughes AJ and Biggs BA. Parasitic worms of the central nervous system: an Australian perspective. Intern Med J, 2002. 32(ll):541-53. Moore AC, Lutwick LI, Schantz PM, Pilcher JB, Wilson M, Hightower AW, Chapnick EK, Abter EI, Grossman JR, Fried JA, and et al. Seroprevalence of cysticercosis in an Orthodox Jewish community. Am J Trop Med Hyg, 1995. 53(5):439-42. Hira PR, Francis I, Abdella NA, Gupta R, Ai-Ali FM, Grover S, Khalid N, Abdeen S, Iqbal J, Wilson M, and Tsang VC. Cysticercosis: imported and autochthonous infections in Kuwait. Trans R Soc Trop Med Hyg, 2004. 98(4):233-9.
150
162. 163.
164.
165.
166.
167. 168.
169.
170. 171. 172.
173. 174. 175. 176.
177.
178.
Al Shahrani D, Frayha HH, Dabbagh O, and Al Shail E. First case of neurocysticercosis in Saudi Arabia. J Trop Pediatr, 2003. 49(l):58-60. Rajshekhar V, Joshi DD, Doanh NQ, van De N, and Xiaonong Z. Taenia solium taeniosis/cysticercosis in Asia: epidemiology, impact and issues. Acta Trop, 2003. 87(l):53-60. van Hout B, Gagnon D, Souetre E, Ried S, Remy C, Baker G, Genton P, Vespignani H, and McNulty P. Relationship between seizure frequency and costs and quality of life of outpatients with partial epilepsy in France, Germany, and the United Kingdom. Epilepsia, 1997. 38(11): 1221-6. Avode DG, Capo-Chichi OB, Gandaho P, Bouteille B, and Dumas M. [Epilepsy caused by cysticercosts. Apropos of a sociological and cultural investigation conducted at Savalou in Benin]. Bull Soc Pathol Exot, 1996. 89(l):45-7. Thomas SV, Sarma PS, Alexander M, Pandit L, Shekhar L, Trivedi C, and Vengamma B. Economic burden of epilepsy in India. Epilepsia, 2001. 42(8):1052-60. Krishnan A, Sahariah SU, and Kapoor SK. Cost of epilepsy in patients attending a secondary-level hospital in India. Epilepsia, 2004. 45(3):289-91. Preux PM, Tiemagni F, Fodzo L, Kandem P, Ngouafong P, Ndonko F, Macharia W, Dongmo L, and Dumas M. Antiepileptic therapies in the Mifi Province in Cameroon. Epilepsia, 2000. 41(4):432-9. Rajkotia Y LA, Gilman RH, Cornejo C, Garcia HH for the Cysticercosis Working Group in Peru. Economic burden of neurocysticercosis: results from Peru. Trans R Soc Trop Med Hyg, 2007. Roberts T, Murrell KD, and Marks S. Economic losses caused byfoodborne parasitic diseases. Parasitol Today, 1994. 10(11):419-23. Griffiths RI, Schrammel PN, Morris GL, Wills SH, Labiner DM, and Strauss MJ. Payer costs of patients diagnosed with epilepsy. Epilepsia, 1999. 40(3):351-8. Zoli A, Shey-Njila O, Assana E, Nguekam JP, Dorny P, Brandt J, and Geerts S. Regional status, epidemiology and impact of Taenia solium cysticercosis in Western and Central Africa. Acta Trop, 2003. 87(l):35-42. Flisser A. Neurocysticercosis in Mexico. Parasitol Today, 1988. 4:131-137. Murrell KD. Economic losses resulting from food-borne parasitic zoonoses. Southeast Asian J Trop Med Public Health, 1991. 22 Suppl:377-81. The marketing of cysticercotic pigs in the Sierra of Peru. The Cysticercosis Working Group in Peru. Bull World Health Organ, 1993. 71(2):223-8. Acevedo A, Economic impact of porcine cysticercosis, in Cysticercosis: Present State of Knowledge and Perspectives, A Flisser, Willms, K., Laclette, J.P., Larralde, C , Ridaura, C , Beltran, F., Editor. 1982, Academic Press: New York. 63-68. Carabin H, Krecek RC, Cowan LD, Michael L, Foyaca-Sibat H, Nash T, and Willingham AL. Estimation of the cost of Taenia solium cysticercosis in Eastern Cape Province, South Africa. Trop Med Int Health, 2006. 11(6):906-16. Allan JC, Craig PS, and Pawlowski ZS, Control of Taenia solium with emphasis on Treatment ofTaeniasis, in Taenia solium cysticercosis. From basic to clinical science., G Singh and S Prabhakar, Editors. 2002, CABI Publishing: Oxon. 411420.
151
179.
180.
181.
182.
183.
184.
185.
186.
187.
188.
189.
190.
191.
Flisser A, Rodriguez-Canul R, and Willingham AL, 3rd. Control of the taeniosis/cysticercosis complex: future developments. Vet Parasitol, 2006. 139(4):283-92. Allan JC, Velasquez-Tohom M, Fletes C, Torres-Alvarez R, Lopez-Virula G, Yurrita P, Soto de Alfaro H, Rivera A, and Garcia-Noval J. Mass chemotherapy for intestinal Taenia solium infection: effect on prevalence in humans and pigs. Trans R Soc Trop Med Hyg, 1997. 91(5):595-8. Diaz Camacho S, Candil Ruiz A, Uribe Beltran M, and Willms K. Serology as an indicator of Taenia solium tapeworm infections in a rural community in Mexico. Trans R Soc Trop Med Hyg, 1990. 84(4):563-6. Diaz Camacho SP, Candil Ruiz A, Suate Peraza V, Zazueta Ramos ML, Felix Medina M, Lozano R, and Willms K. Epidemiologic study and control of Taenia solium infections with praziquantel in a rural village of Mexico. Am J Trop Med Hyg, 1991. 45(4):522-31. Cruz M, Davis A, Dixon H, Pawlowski ZS, and Proano J. Operational studies on the control of Taenia solium taeniasis/cysticercosis in Ecuador. Bull World Health Organ, 1989. 67(4):401-7. Keilbach NM, de Aluja AS, and Sarti-Gutierrez E. A programme to control taeniasis-cysticercosis (T. solium): experiences in a Mexican village. Acta Leiden, 1989. 57(2): 181-9. Rodriguez-Canul R, Fraser A, Allan JC, Dominguez-Alpizar JL, ArgaezRodriguez F, and Craig PS. Epidemiological study of Taenia solium taeniasis/cysticercosis in a rural village in Yucatan state, Mexico. Ann Trop Med Parasitol, 1999. 93(l):57-67. Sarti E, Schantz PM, Plancarte A, Wilson M, Gutierrez 01, Aguilera J, Roberts J, and Flisser A. Epidemiological investigation of Taenia solium taeniasis and cysticercosis in a rural village ofMichoacan state, Mexico. Trans R Soc Trop Med Hyg, 1994. 88(l):49-52. Sarti E, Schantz PM, Plancarte A, Wilson M, Gutierrez IO, Lopez AS, Roberts J, and Flisser A. Prevalence and riskfactors for Taenia solium taeniasis and cysticercosis in humans and pigs in a village in Morelos, Mexico. Am J Trop Med Hyg, 1992. 46(6):677-85. Mafojane NA, Appleton CC, Krecek RC, Michael LM, and Willingham AL, 3rd. The current status of neurocysticercosis in Eastern and Southern Africa. Acta Trop, 2003. 87(l):25-33. Garcia HH, Gilman RH, Tovar MA, Flores E, Jo R, Tsang VC, Diaz F, Torres P, and Miranda E. Factors associated with Taenia solium cysticercosis: analysis of nine hundredforty-six Peruvian neurologic patients. Cysticercosis Working Group in Peru (CWG). Am J Trop Med Hyg, 1995. 52(2): 145-8. Ortiz-Trejo JM, Correa-Chacon AJ, Sctelo-Ham EI, Torres-Valenzuela A, and Alvarado-Esquivel C. [Risk factors associated with neurocysticercosis in a public hospital in Mexico]. Gac Med Mex, 2006. 142(3): 175-9. Garcia HH, Gilman RH, Gonzalez AE, Pacheco R, Verastegui M, and Tsang VC. Human and porcine Taenia solium infection in a village in the highlands of Cusco, Peru. The Cysticercosis Working Group in Peru. Acta Trop, 1999. 73(l):31-6.
152
192.
193.
194.
195.
196.
197.
198.
199.
200.
201.
202.
203.
Nguekam JP, Zoli AP, Zogo PO, Kamga AC, Speybroeck N, Domy P, Brandt J, Losson B, and Geerts S. A seroepidemiological study of human cysticercosis in West Cameroon. Trop Med Int Health, 2003. 8(2): 144-9. Schantz PM, Sarti E, Plancarte A, Wilson M, Criales JL, Roberts J, and Flisser A. Community-based epidemiological investigations of cysticercosis due to Taenia solium: comparison of serological screening tests and clinical findings in two populations in Mexico. Clin Infect Dis, 1994. 18(6):879-85. Moro PL, Lopera L, Bonifacio N, Gilman RH, Silva B, Verastegui M, Gonzales A, Garcia HH, and Cabrera L. Taenia solium infection in a rural community in the Peruvian Andes. Ann Trop Med Parasitol, 2003. 97(4):373-9. Carrique-Mas J, Iihoshi N, Widdowson MA, Roca Y, Morales G, Quiroga J, Cejas F, Caihuara M, Ibarra R, and Edelsten M. An epidemiological study of Taenia solium cysticercosis in a rural population in the Bolivian Chaco. Acta Trop, 2001. 80(3):229-35. Garcia-Garcia ML, Torres M, Correa D, Flisser A, Sosa-Lechuga A, Velasco O, Meza-Lucas A, Plancarte A, Avila G, Tapia R, Aguilar L, Mandujano A, Alcantara I, Morales Z, Salcedo A, Manon MD, and Valdespino-Gomez JL. Prevalence and risk of cysticercosis and taeniasis in an urban population of soldiers and their relatives. Am J Trop Med Hyg, 1999. 61(3):386-9. Cao W, van der Ploeg CP, Xu J, Gao C, Ge L, and Habbema JD. Risk factors for human cysticercosis morbidity: a population-based case- control study. Epidemiol Infect, 1997. 119(2):231-5. Garcia HH, Araoz R, Gilman RH, Valdez J, Gonzalez AE, Gavidia C, Bravo ML, and Tsang VC. Increased prevalence of cysticercosis and taeniasis among professional fried pork vendors and the general population of a village in the Peruvian highlands. Cysticercosis Working Group in Peru. Am J Trop Med Hyg, 1998. 59(6):902-5. Sanchez AL, Medina MT, and Ljungstrom I. Prevalence of taeniasis and cysticercosis in a population of urban residence in Honduras. Acta Trop, 1998. 69(2): 141-9. Fleury A, Gomez T, Alvarez I, Meza D, Huerta M, Chavarria A, Carrillo Mezo RA, Lloyd C, Dessein A, Preux PM, Dumas M, Larralde C, Sciutto E, and Fragoso G. High prevalence of calcified silent neurocysticercosis in a rural village of Mexico. Neuroepidemiology, 2003. 22(2): 139-45. Garcia HH, Gonzalez AE, Gilman RH, Moulton LH, Verastegui M, Rodriguez S, Gavidia C, and Tsang VC. Combined human and porcine mass chemotherapy for the control ofT. solium. Am J Trop Med Hyg, 2006. 74(5):850-5. Widdowson MA, Cook AJ, Williams JJ, Argaes F, Rodriguez I, Dominguez JL, and Rodriguez R. Investigation of risk factors for porcine Taenia solium cysticercosis: a multiple regression analysis of a cross-sectional study in the Yucatan Peninsula, Mexico. Trans R Soc Trop Med Hyg, 2000. 94(6):620-4. Ngowi HA, Kassuku AA, Maeda GE, Boa ME, Carabin H, and Willingham AL, 3rd. Riskfactors for the prevalence of porcine cysticercosis in Mbulu District, Tanzania. Vet Parasitol, 2004. 120(4):275-83.
153
204.
205.
206.
207.
208. 209.
210.
211. 212. 213.
214.
215. 216.
217.
218.
Sikasunge CS, Phiri IK, Phiri AM, Domy P, Siziya S, and Willingham AL, 3rd. Risk factors associated with porcine cysticercosis in selected districts of Eastern and Southern provinces of Zambia. Vet Parasitol, 2007. 143(l):59-66. Morales J, Velasco T, Tovar V, Fragoso G, Fleury A, Beltran C, Villalobos N, Aluja A, Rodarte LF, Sciutto E, and Larralde C. Castration and pregnancy of rural pigs significantly increase the prevalence of naturally acquired Taenia solium cysticercosis. Vet Parasitol, 2002. 108(l):41-8. Morales J, Martinez JJ, Garcia-Castella J, Pena N, Maza V, Villalobos N, Aluja AS, Fleury A, Fragoso G, Larralde C, and Sciutto E. Taenia solium: the complex interactions, of biological, social, geographical and commercial factors, involved in the transmission dynamics of pig cysticercosis in highly endemic areas. Ann Trop Med Parasitol, 2006. 100(2):123-35. Boa ME, Mahundi EA, Kassuku AA, Willingham AL, 3rd, and Kyvsgaard NC. Epidemiological survey of swine cysticercosis using ante-mortem and postmortem examination tests in the southern highlands of Tanzania. Vet Parasitol, 2006. 139(l-3):249-55. Lawson JR and Gemmell MA. Hydatidosis and cysticercosis: the dynamics of transmission. Adv Parasitol, 1983. 22:261-308. Diaz F, Garcia HH, Gilman RH, Gonzales AE, Castro M, Tsang VC, Pilcher JB, Vasquez LE, Lescano M, Carcamo C, and et al. Epidemiology oftaeniasis and cysticercosis in a Peruvian village. The Cysticercosis Working Group in Peru. Am J Epidemiol, 1992. 135(8):875-82. Silverman PH and Griffiths RB. A review of methods of sewage disposal in Great Britain, with special reference to the epizootiology of Cysticercus bovis. Ann Trop Med Parasitol, 1955. 49(4):436-50. Guildal J A. Mogers betydning som spredereaf baendelomeaeg. Nord Vet Med, 1956(8):727-733. Gladkov GN. Wild birds as possible vectors of Taenia saginata oncospheres. Problemy Parazitologii, 1969. 1:69. Zmee GI. On the importance of certain synanthropic insects as carriers and intermediate hosts of parasitic worms in Tadzhikistan. Trudy Tadzhikskoi Bazy AkademiyaNauk S.S.S.R., 1936. 6:241-248. Nadzhafov IG. The role of different species of synanthropic flies in dissemination of oncospheres ofTaeniarhynchus saginatus. Meditsinskaya Parasitologya i Parazitarnye Bolezni, 1967. 36:144-149. Lawson JR and Gemmell MA. Transmission oftaeniid tapeworm eggs via blowflies to intermediate hosts. Parasitology, 1990. 100 Pt 1:143-6. Martinez MJ, De Aluja AS, and Gemmell M. Failure to incriminate domestic flies (Diptera: Muscidae) as mechanical vectors of Taenia eggs (Cyclophyllidea: Taeniidae) in rural Mexico. J Med Entomol, 2000. 37:489-491. Murrell KD, Epidemiology ofTaeniosis and Cysticercosis, in WHO/FAO/OIE Guidelines for the Surveillance, Prevention and Control of Taeniasis/Cysticercosis, KD Murrell, Editor. 2005: Geneva, Switzerland. 27-43. Zenkov AV. Some problems in the epizootiology of Cysticercus cellulosae infection in the Bielorussian, S.S.R. Trudy Belousskogo Nauchno-Issledovatel'skogo Institua Eksperimental'noi Veterinarii, 1978. 16:92-95.
154
219.
220.
221.
222. 223. 224.
225. 226.
227.
228.
229.
230.
231.
232.
Archipova NS. role of certain insects in the dissemination of Cysticercus bovis amongst cattle. Byulletin' Vesesoyuznogo Instituta Gel'mintologii im K.I. Skryabina, 1975. 16:10-12. Gonzalez AE, Lopez-Urbina T, Tsang BY, Gavidia CM, Garcia HH, Silva ME, Ramos DD, Manzanedo R, Sanchez-Hidalgo L, Gilman RH, and Tsang VC. Short report: secondary transmission in porcine cysticercosis: description and their potential implications for control sustainability. Am J Trop Med Hyg, 2005. 73(3):501-3. Gonzalez AE, Lopez-Urbina T, Tsang B, Gavidia C, Garcia HH, Silva ME, Ramos DD, Manzanedo R, Sanchez-Hidalgo L, Gilman RH, and Tsang VC. Transmission dynamics of Taenia solium and potential for pig-to-pig transmission. Parasitol Int, 2006. 55 Suppl:S131-5. Hutchings MR, Athanasiadou S, Kyriazakis I, and Gordon IJ. Can animals use foraging behaviour to combat parasites? Proc Nutr Soc, 2003. 62(2):361-70. Recommendations of the International Task Force for Disease Eradication. MMWR Recomm Rep, 1993. 42(RR-16):l-38. International Task Force for Disease Eradication. Summary of the Fourth Meeting of the ITFDE(II). 2003, International Task Force for Disease Eradication: New York. 4. Lightowlers MW. Eradication of Taenia solium cysticercosis: a role for vaccination of pigs. Int J Parasitol, 1999. 29(6):811-7. Lawson JR and Gemmell MA. The ovine cysticercosis as models for research into the epidemiology and control of the human and porcine cysticercosis Taenia solium: II. The application of control. Acta Leiden, 1989. 57(2): 173-80. Gonzalez AE, Garcia HH, Gilman RH, Tsang VCW, and The Cysticercosis Working Group in Peru. Control of Taenia solium. Acta Tropica, 2003. 87:103109. Sarti E, Schantz PM, Avila G, Ambrosio J, Medina-Santillan R, and Flisser A. Mass treatment against human taeniasisfor the control of cysticercosis: a population-based intervention study. Trans R Soc Trop Med Hyg, 2000. 94(1):859. Pawlowski Z, Allan J, and Sarti E. Control of Taenia solium taeniasis/cysticercosis: From research towards implementation. Int J Parasitol, 2005. Sarti E, Flisser A, Schantz PM, Gleizer M, Loya M, Plancarte A, Avila G, Allan J, Craig P, Bronfman M, and Wijeyaratne P. Development and evaluation of a health education intervention against Taenia solium in a rural community in Mexico. Am J Trop Med Hyg, 1997. 56(2):127-32. Lightowlers MW, Rolfe R, and Gauci CG. Taenia saginata: vaccination against cysticercosis in cattle with recombinant oncosphere antigens. Exp Parasitol, 1996. 84(3):330-8. Flisser A, Gauci CG, Zoli A, Martinez-Ocana J, Garza-Rodriguez A, DominguezAlpizar JL, Maravilla P, Rodriguez-Canul R, Avila G, Aguilar-Vega L, Kyngdon C, Geerts S, and Lightowlers MW. Induction of protection against porcine cysticercosis by vaccination with recombinant oncosphere antigens. Infect Immun, 2004. 72(9):5292-7.
155
233. 234. 235.
236.
237. 238. 239. 240. 241. 242.
243.
244.
245.
246.
247.
248.
Lightowlers MW. Vaccines against cysticercosis and hydatidosis: foundations in taeniid cestode immunology. Parasitol Int, 2006. 55 Suppl:S39-43. Lightowlers MW. Cestode vaccines: origins, current status andfuture prospects. Parasitology, 2006. 133 Suppl:S27-42. Sanchez AL, Gomez O, Allebeck P, Cosenza H, and Ljungstrom L. Epidemiological study of Taenia solium infections in a rural village in Honduras. Ann Trop Med Parasitol, 1997. 91(2): 163-71. Instituto Nacional de Estadistica e Informatica. Ill Censo de Poblacion y Vivienda - Informe Final (Spanish). 1993, Instituto Nacional de Estadistica e Informatica: Lima, Peru. Ritchie LS. An ether sedimentation technique for routine stool examination. Bull US Army Med Dept, 1948. 8:326. Engel HN and Claire LE, Anatomy, in Diseases of Swine, AD Leman, BE Straw, and WL Mengeling, Editors. 1986, Iowa State University Press: Ames, IA. 3-25. Microsoft Corporation. Microsoft Encarta Online Encyclopedia. 2004: Redmond, WA. Available from http://encarta.msn.com. Nelder JA and Wedderburn RWM. Generalized Lineal Models. J R Stat Soc Ser A, 1972. 135:370-384. Allan JC, Wilkins PP, Tsang VC, and Craig PS. Immunodiagnostic tools for taeniasis. Acta Trop, 2003. 87(l):87-93. Garcia HH and Del Brutto OH. Heavy nonencephalitic cerebral cysticercosis in tapeworm carriers. The Cysticercosis Working Group in Peru. Neurology, 1999. 53(7): 1582-4. Gilman RH, Del Brutto OH, Garcia HH, and Martinez M. Prevalence oftaeniosis among patients with neurocysticercosis is related to severity of infection. TheCysticercosis Working Group in Peru. Neurology, 2000. 55(7): 1062. Lescano AG, Garcia HH, Gilman RH, Guezala MC, Tsang VC, Gavidia CM, Rodriguez S, Moulton LH, Green JA, and Gonzalez AE. Swine cysticercosis hotspots surrounding Taenia solium tapeworm carriers. Am J Trop Med Hyg, 2007. 76(2):376-83. Montano SM, Villaran MV, Ylquimiche L, Figueroa J J, Rodriguez S, Bautista CT, Gonzalez AE, Tsang VC, Gilman RH, and Garcia HH. Neurocysticercosis: association between seizures, serology, and brain CT in rural Peru. Neurology, 2005. 65(2):229-33. Jafri HS, Torrico F, Noh JC, Bryan RT, Balderrama F, Pilcher JB, and Tsang VC. Application of the enzyme-linked immunoelectrotransfer blot to filter paper blood spots to estimate seroprevalence of cysticercosis in Bolivia. Am J Trop Med Hyg, 1998. 58(3):313-5. Peralta RH, Macedo HW, Vaz AJ, Machado LR, and Peralta JM. Detection of anti-cysticercus antibodies by ELISA using whole blood collected on filter paper. Trans R Soc Trop Med Hyg, 2001. 95(l):35-6. Fleury A, Bouteille B, Garcia E, Marquez C, Preux PM, Escobedo F, Sotelo J, and Dumas M. Neurocysticercosis: validity of ELISA after storage of whole blood and cerebrospinal fluid on paper. Trop Med Int Health, 2001. 6(9):688-93.
156
249.
250.
%
251.
252.
253.
254.
255.
256.
257.
258.
259.
260. 261.
262.
Placencia M, J.W. S, Shorvon SD, Ellison RH, and Cascante SM. Validation of a screening questionnaire for the detection of epileptic seizures in epidemiological studies. Brain, 1992. 115:783-794. Placencia M, Suarez J, Crespo F, Sander JW, Shorvon SD, Ellison RH, and Cascante SM. A large-scale study of epilepsy in Ecuador: methodological aspects. Neuroepidemiology, 1992. ll(2):74-84. Commission on classification and Terminology of the International League Against Epilepsy. Proposal for revised clinical and electroencephalographs classification of epileptic seizures. Epilepsia, 1981. 22:489-501. Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia, 1989. 30(4):389-99. Gemmell MA. The Styx Field Trial: effect of treatment of the definitive host for tapeworms on larval forms in the intermediate host. Bull World Health Organ, 1978. 56(3):433-43. Huisa BN, Menacho LA, Rodriguez S, Bustos JA, Gilman RH, Tsang VC, Gonzalez AE, and Garcia HH. Taeniasis and cysticercosis in housemaids working in affluent neighborhoods in Lima, Peru. Am J Trop Med Hyg, 2005. 73(3):496500. Singh G, Ram S, Kaushal V, Kumar S, Bhatia RC, Raizada N, and Kaushal RK. Risk of seizures and neurocysticercosis in householdfamily contacts of children with single enhancing lesions. J Neurol Sci, 2000. 176(2):131-5. Leontsini E. Educational interventions in Taeniasis/Cysticercosis. in 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene. 2005. Washington, DC. Lescano AG, Garcia HH, Gilman RH, Guezala MC, Tsang VCW, Rodriguez S, Moulton LH, Villaran MV, Montano SM, Gonzalez AE, and Peru aTCWGi. Human cysticercosis hotspots surrounding Taenia solium tapeworm carriers, in 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene. 2005. Washington, DC. Tello R. Empleo de una nueva tecnica parasitologica rdpida de sedimentacion espontdnea en el diagnostico de protozoarios y helmintos. in VJornadas Cientiflcas de la Universidad Peruana Cayetano Heredia. 1998. Lima, Peru. Jimenez J, Levine MZ, Rodriguez S, Garcia HH, Gonzalez AE, Gilman RH, Tsang VCW, and Peru. TCWGi. Evaluation of an Enzyme-Linked Immunoelectrotransfer Blot Assay Using the Recombinant Antigen rES33for Stage-Specific Serological Diagnosis of Taeniasis due to Taenia Solium, in 53th Annual Meeting of the American Society of Tropical Medicine and Hygiene. 2004. Miami, FL. Judge GG, Griffiths WE, Hill RC, Luktkepohl H, and Lee TC, The theory and practice of econometrics. 2nd Edition ed. 1985, New York City, NY: Wiley. Flisser A, Sarti E, Lightowlers M, and Schantz P. Neurocysticercosis: regional status, epidemiology, impact and control measures in the Americas. Acta Trop, 2003. 87(1):43-51. Greenland S. Dose-response and trend analysis in epidemiology: alternatives to categorical analysis. Epidemiology, 1995. 6(4):356-65.
157
263.
264.
265. 266. 267.
268.
269. 270.
271.
272.
273.
Pawlowski ZS. Control of Taenia solium taeniasis and cysticercosis by focusoriented chemotherapy of taeniasis. Southeast Asian J Trop Med Public Health, 1991.22Suppl:284-6. Craig PS, Rogan MT, and Allan JC. Detection, screening and community epidemiology oftaeniid cestode zoonoses: cystic echinococcosis, alveolar echinococcosis and neurocysticercosis. Adv Parasitol, 1996. 38:169-250. Foege WH, Millar JD, and Lane JM. Selective epidemiologic control in smallpox eradication. Am J Epidemiol, 1971. 94(4):311-5. Hull HF, Birmingham ME, Melgaard B, and Lee JW. Progress toward global polio eradication. J Infect Dis, 1997. 175 Suppl l:S4-9. Longini IM, Jr., Nizam A, Xu S, Ungchusak K, Hanshaoworakul W, Cummings DA, and Halloran ME. Containing pandemic influenza at the source. Science, 2005. 309(5737): 1083-7. Ferguson NM, Cummings DA, Cauchemez S, Fraser C, Riley S, Meeyai A, Iamsirithaworn S, and Burke DS. Strategies for containing an emerging influenza pandemic in Southeast Asia. Nature, 2005. 437(7056):209-14. World Health Organization. WHO pandemic influenza draft protocol for rapid response and containment (Draft). 2006, World Health Organization: Geneva. 50. International Task Force for Disease Eradication. Recommendations of the International Task Force for Disease Eradication. MMWR Morb Mortal Wkly Rep, 1993. 42(RR-16):l-38. Jimenez J, Rodriguez S, Levine MZ, Zamora H, Castillo Y, Allan JC, Gonzalez AE, Tsang VCW, Gilman RH, Garcia HH, and Peru fTCWGi. Human Taeniasis: Diagnosis and Assessment, in 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene. 2005. Washington, DC. Gonzalez AE. Evaluation of a control programme for Taenia solium targeting human and porcine health, in Veterinary Epidemiology. 1997, University of Reading: Reading, UK. Rodriguez S, Silva ME, Jimenez J, Brandt J, Tsang VCW, Gonzalez AE, Gilman RH, Dorny P, and Garcia HH. Human neurocysticercosis: antigen and antibody detection in urine samples, in 53rd Annual Meeting of the American Society of Tropical Medicine and Hygiene. 2004. Miami, FL.
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CURRICULUM VITAE INSTITUTION AND LOCATION
Universidad Nacional de Ingenieria, Lima - Peru Universidad Peruana Cayetano Heredia, Lima - Peru Johns Hopkins School of Hygiene and Public Health, Baltimore, MD
DEGREE
YEAR(S)
FIELD OF STUDY
B.S.
1985-1991
M.Sc.
1994-1998
M.H.S. M.H.S. Ph.D
Systems Engineering Informatics
1998-2000 2001-2002 Biostatistics 1998Health Policy P resent International Health
mi
Positions and Honors PRISMA, Research Department. Lima - Peru. Head of the Information Systems Unit. Consultant in Biostatistics and Epidemiology Universidad Peruana Cayetano Heredia, Public Health Department. Lima 1994-1996 - Peru. Assistant Professor and Coordinator of the Teaching Support Unit Ministry of Health, Basic Health and Nutrition Project, Lima - Peru. 1995 Consultant in Data Management Universidad Nacional Mayor de San Marcos, Veterinary Medicine 1995-1997 School, Lima-Peru. Guest lecturer. Universidad Peruana Cayetano Heredia, Pathology Department, Lima 1995-1998 Peru. Consultant in Biostatistics and Associate Investigator Universidad Peruana Cayetano Heredia, Institute of Tropical Medicine 1996 -1997 Alexander Von Humboldt. Consultant in Biostatistics. Ministry of Health, Basic Health and Nutrition Project, Lima - Peru. 1998 Consultant in Informatics and Monitoring 1998AB PRISMA, Research Department, Lima - Peru. Consultant in present Biostatistics and Epidemiology 1991-1998
1998-1999
1998-1999 1999-2000 2000present 2000-2001 2000-2001
Johns Hopkins University, Vaccine Testing Unit, Baltimore, MD. Data Analyst
Johns Hopkins University, Center for Hospital Finance and Management, Baltimore, MD. Consultant in Biostatistics Johns Hopkins University, School of Hygiene and Public Health, Department of Epidemiology and Department of Population and Family Sciences, Baltimore, MD. Teaching Assistant and tutor Johns Hopkins University, School of Hygiene and Public Health, Departments of International Health and Environmental Health Sciences, Baltimore, MD. Consultant in Biostatistics Johns Hopkins University, School of Hygiene and Public Health, Summer Institute in Tropical Medicine and Public Health. Baltimore, MD. Lecturer in Epidemiology and Biostatistics Centers for Disease Control and Prevention, Parasitic Disease Branch.
159
_ ftni 2001present 2002present 2002-
_ 2003present
Atlanta, GA. Consultant in Biostatistics University of Maryland School of Medicine, Malaria Section, Center for Vaccine Development, Baltimore, MP. Consultant in Biostatistics Universidad Peruana Cayetano Heredia, School of Public Health and Management. Lima - Peru. Associate Professor Graduate School of Business Administration (ESAN), MBA Program, Lima - Peru. Part Time Professor. United States Naval Medical Research Center Detachment (USNMRCD), Global Emerging Infections Program (GEIS), Lima - Peru. Training Coordinator and Research Scientist Universidad Peruana Cayetano Heredia, Department of Parasitology. Lima - Peru. Consultant in Epidemiology and Biostatistics.
Peer-Reviewed Publications (in chronological order) 1. Rajkotia Y, Lescano AG, Gilman RH, Cornejo C, Garcia HH. Economic burden of cysticercosis in Peru. Accepted for publication at Trans R Soc Trop Med Hyg 2. Konda KA, Lescano AG. Leontsini E, Fernandez P, Klausner JD, Celentano DD, Coates TJ, Caceres CF, and the NIMH Collaborative HIV/STI Prevention Trial Group. Sexual behavior and condom use among heterosexually-identified men with high rates of recent MSM behavior in low-income, urban, coastal Peru. AIDS Behav. 2007 Mar 22 3. Jones FR, Miller G, Gadea N, Meza R, Leon S, Perez J, Lescano AG, Pajuelo J, Caceres CF, Klausner JD, Coates TJ; the NIMH Collaborative HIV/STI Prevention Trial Group. Prevalence of bacterial vaginosis among young women in low-income populations of coastal Peru. Int J STD AIDS. 2007 Mar; 18(3): 188-92 4. Lescano AG. Garcia HH, Gilman RH, Guezala MC, Tsang VCW, Gavidia CM, Rodriguez S, Moulton LH, Green JA, Gonzalez AE and the Cysticercosis Working Group in Peru. Swine cysticercosis hotspots surrounding Taenia solium tapeworm carriers. Am J Trop Med Hyg. 2007 Feb;76(2):376-383
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5. Jones FR, Ortiz M, Soriano I, Utz G, Saldarriaga E, Cumpa R, Collantes V, Leandro Y, Bernal MM, Ucanan LE, Colina O, Lescano AG, Batsel TM. Outbreak of gastroenteritis at a Peruvian naval base. Mil Med. 2006 Oct; 171(11): 1095-9 6. Torres-Slimming P, Mundaca C, Quispe J, Colina O, Bacon D, Lescano AG, Gilman RH, Blazes DL. Outbreak of Cyclosporiasis at a Naval Base in Lima, Peru. Am J Trop Med Hyg. 2006 Sep;75(3):546-8 7. Lescano AG, Ayala EN, Gilman RH, Calderon M, Pinedo VV, Terry H, Cabrera L and Vinetz JM. Polymerase Chain Reaction and Molecular Genotyping to Monitor Parasitological Response to Anti-Malarial Chemotherapy in the Peruvian Amazon. Am J Trop Med Hyg. 2006 Apr;74(4):546-553 8. Clark JL, Coates TJ, Lescano AG, Castillo R, Meza R, Jones FR, Leon S, Pajuelo J, Caceres CF, Klausner JD. Different positive predictive values of commercially available human immunodeficiency virus enzyme-linked immunosorbent assays. Clin Vaccine Immunol. 2006 Feb;13(2):302-3. 9. Priest JW, Bern C, Xiao L, Roberts JM, Kwon JP, Lescano AG. Checkley W, Cabrera L, Moss DM, Arrowood MJ, Sterling CR, Gilman RH, Lammie PJ. Longitudinal analysis of Cryptosporidium species-specific immunoglobulin G antibody responses in Peruvian children. Clin Vaccine Immunol. 2006 Jan;13(l):123-31 10. Priest JW, Bern C, Roberts JM, Kwon JP, Lescano AG. Checkley W, Cabrera L, Moss DM, Arrowood MJ, Sterling CR, Gilman RH, Lammiel PJ. Changes in Serum Immunoglobulin G Levels as a Marker for Cryptosporidium sp. Infection in Peruvian Children. J Clin Microbiol. 2005 Oct;43(10):5298-300
11. Konda KA, Klausner JD, Lescano AG, Leon S, Jones FR, Pajuelo J, Caceres CF, Coates TJ; The NIMH Collaborative HIV/STI Prevention Trial Group. The Epidemiology of Herpes Simplex Virus Type 2 Infection in Low-Income Urban Populations in Coastal Peru. Sex Transm Dis. 2005 Sep;32(9):534-541 12. Cumbo TA, Braude D, Basnyat B, Rabinowitz L, Lescano AG, Shah MB, Radder DJ, Bashyal G, Gambert SR. Higher Venous Bicarbonate Concentration Associated with Hypoxemia, not Acute Mountain Sickness, after Ascent to Moderate Altitude. J Travel Med. 2005 Jul-Aug; 12(4): 184-9 13. Jeri C, Gilman RH, Lescano AG, Mayta H, Ramirez ME, Gonzalez AE, Nazerali R, Garcia HH. Species identification after treatment for human taeniasis. Lancet, 2004 Mar; 363(9413): 949-50 14. Santiago EM, Lawson E, Gillenwater K, Kalangi S, Lescano AG, Du Quella G, Cummings K, Cabrera L, Torres C, Gilman RH. A Prospective Study of Bacillus Calmette-Guerin Scar Formation and Tuberculin Skin Test Reactivity in Infants in Lima, Peru. Pediatrics. 2003 Oct;112(4):E298 15. Roshanravan B, Kari E, Gilman RH, Cabrera L, Lee E, Metcalfe J, Calderon M, Lescano AG, Montenegro S, Calampa C, Vinetz JM. Endemic malaria in the Peruvian Amazon region oflquitos. Am J Trop Med Hyg. 2003 Jul;69(l):45-52 16. Olender S, Apgar J, Saito M, Bautista C, Lescano AG, Moro P, Caviedes L, Hsieh E, Gilman RH. Lower rates of tuberculosis transmission and family clustering at high altitude in Peru. Am J Trop Med Hyg. 2003 Jun;68(6):721-7. 17. Garcia HH, Gilman RH, Gonzalez AE, Verastegui M, Rodriguez S, Gavidia C, Tsang VC, Falcon N, Lescano AG, Moulton LH, Bernal T, Tovar M. Hyperendemic human
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and porcine Taenia solium infection in Peru. Am J Trop Med Hyg. 2003 Mar;68(3):268-75. 18. Cumbo TA, Basnyat B, Graham J, Lescano AG and Gambert S. Acute Mountain Sickness, Dehydration, and Bicarbonate Clearance: Preliminary Field Data from the Nepal Himalaya. Aviat Space Environ Med 2002;73:898-901 19. Bern C, Ortega Y, Checkley W, Roberts JM, Lescano AG, Cabrera L, Verastegui M, Black RE, Sterling C, and Gilman RH. Epidemiologic differences between Cyclospora and Cryptosporidium in a cohort study of Peruvian children. EID 2002 Jun;8(6):581-5 20. Delgado J, Ramirez-Cardich ME, Gilman RH, Lavarello R, Dahodwala N, Bazan A, Rodriguez V, Cama RI, Tovar M, Lescano A. Risk factors for burns in children: crowding, poverty and poor maternal education. Inj Prev 2002, Mar,8(l):38-41 21. Berkman DS, Lescano AG. Gilman RH, Black MM and Lopez S. Stunting, Diarrheal Disease and Parasitic Infections in Peruvian Infants: Their Effect on Cognitive Test Scores in Late Childhood. Lancet 2002; 359:564-71 22. Checkley W, Gilman RH, Black RE, Lescano AG, Cabrera L, Taylor DN and Moulton LH. Effects of nutritional status on diarrheal disease in Peruvian Children. J Pediatr 2002 Feb; 140:210-8 23. Kublin JG, Dzinjalamala FK, Kamwendo DD, Malkin EM, Cortese JF, Martino LM, Mukadam RAG, Rogerson SJ, Lescano AG, Molyneux ME, Winstanley PA, Chimpeni P, Taylor TE and Plowe CV Molecular markers for treatment failure of sulfadoxine-pyrimethamine and chlorproguanil-dapsone for falciparum malaria and a model for practical application in Africa. J Infect Dis 2002;185:380-8
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24. Chowdhury HR, Yunus M, Zaman K, Rahman A, Faruque SM, Lescano AG, Sack RB. The efficacy of bismuth subsalicylate in the treatment of acute diarrhoea and the prevention of persistent diarrhoea. Acta Paediatr. 2001 Jun;90(6):605-10. 25. Kosek M, Lavarello R, Gilman RH, Delgado J, Maguina-Vargas C, Verastegui M, Lescano AG, Mallque V, Kosek JC, Recavarren S and Cabrera L. Natural history of infection with B bacilliformis in a non-endemic population. J Infect Dis 2000 Aug;182(3):865-872 26. Moro PL, Checkley W, Gilman RH, Cabrera L, Lescano AG, Bonilla JJ, Silva B. Gallstone disease in Peruvian coastal natives and highland migrants. Gut. 2000 Apr;46(4):569-73 27. Moro PL, Checkley W, Gilman RH, Lescano G, Bonilla JJ, Silva B, Garcia HH. Gallstone disease in high-altitude Peruvian rural populations. Am J Gastroenterol 1999 Jan;94(l): 153-8 28. Oberhelman RA, Gilman RH, Sheen P, Taylor DN, Black RE, Cabrera L, Lescano AG, Meza R, Madico G. A placebo-controlled trial of Lactobacillus GG to prevent diarrhea in undernourished Peruvian children. J Pediat 1999 Jan; 134(1): 15-20 29. Sanghavi DM, Gilman RH, Lescano-Guevara AG, Checkley W, Cabrera LZ, Cardenas V. Hyperendemic pulmonary tuberculosis in a Peruvian shantytown. Am J Epidemiol 1998 Aug 15;148(4):384-9 30. Moro PL, McDonald J, Gilman RH, Silva B, Verastegui M, Malqui V, Lescano G, Falcon N, Montes G, Bazalar H. Epidemiology of Echinococcus granulosus infection in the central Peruvian Andes. Bull World Health Org 1997;75(6):553-61
31. Marin CM, Segura JL, Bern C, Freedman DS, Guillermo-Lescano A, Benavente LE, Cordero LG, Clavijo L, Gilman JB. Seasonal change in nutritional status among young children in an urban shanty town in Peru. Trans R Soc Trop Med Hyg 1996 Jul-Aug;90(4):442-5
Abstracts in International Conferences (last 3 years) •
Lescano AG. Preparing for the Worst: Teaching Outbreak Investigation and Response in the Americas: 2002 - 2006. Oral presentation at the Public Training Symposium, 55th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Atlanta, GA, November, 2006
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Lescano AG, Michaud JM, Salmon-Mulanovich G, Gonzaga VE, Blazes DL. CaseControl and Retrospective Cohort Studies in Outbreak Investigations, 1986-2005: Update of a Classic Study. Poster and oral presentation at the 55th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Atlanta, GA, November 2006
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Salmon-Mulanovich G, Utz G, Lescano AG, Blazes DL. Rapid Response to a Case of Mumps Prevents an Outbreak at a Research Facility. Poster presentation at the 55th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Atlanta, GA, November 2006
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Gonzaga VE, Salmon-Mulanovich G, Huaman A, Lescano AG, Blazes DL. Histamine in scombroid fish from wholesale and retail markets in Lima, Peru. Poster presentation at the 55th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Atlanta, GA, November 2006
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Lescano AG, Salmon-Mulanovich G, Pedroni E, Suarez-Ognio L, Aguilera X, Gonzaga V, Palomeque J, Badilla X, Batsel TM and Blazes DL. Outbreak Investigation and Response Training in the Americas: Building Public Health Capacity to Confront Global Epidemics. Poster presentation at the XI Meeting of the World Federation of Public Health Associations, Rio de Janeiro, Brazil, August 2125, 2006.
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Lescano AG, Ognibene FP, McPherson D, Salmon-Mulanovich G, Gonzaga V, Montano SM, Suarez-Ognio L, Blazes DL and Gallin JI. The NIH Clinical Center's Clinical Research Videoconference Course and Distance Learning in Peru: A Case Study. Poster presentation at the XI Meeting of the World Federation of Public Health Associations, Rio de Janeiro, Brazil, August 21-25, 2006.
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Munayco CV, Mundaca CC, Araujo RV, Pardo K, Lescano AG, Bolarte J, Blazes DL, Suarez L. EWORS In Peru: A Complementary Surveillance Methodology For Outbreak Detection In A Resource Limited Country. Poster presentation at the XI Meeting of the World Federation of Public Health Associations, Rio de Janeiro, Brazil, August 21-25, 2006.
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Blazes DL, Konda KA, Lescano AG, Franco P, Montano SM, Mulder M, Martin GJ, Castro C, Mendoza C, Alva J, Vallejo V. Sexual risk behavior and condom use by partner type among enlisted military and police trainees in Peru. Poster presentation at the XVI International AIDS Conference. Toronto, Canada, 13-18 August 2006.
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Konda KA, Lescano AG, Sandoval C, Galea JT, Coates TJ, Caceres CF, and the NIMH Collaborative HIV/STD Prevention Trial Group. Forced sex in three socially-
marginalized populations in low-income, urban, coastal Peru. Poster presentation at the XVI International AIDS Conference. Toronto, Canada, 13-18 August 2006. •
Lescano AG, Konda KA, Clark JL, Galea JT, Klausner JD, Jones FR, Leon SR, Caceres CF, Coates TJ and the NIMH Collaborative HIV/STD Prevention Trial Group. Recent onset of STI symptoms, actions to prevent transmission and symptom management in low-income, socially marginalized populations in urban, coastal Peru. Poster presentation at the XVI International AIDS Conference. Toronto, Canada, 1318 August 2006.
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Lescano AG, Corwin AL, Larasati R, Blazes DL, Simanjutak CH, Glass JS. Frequency of Selected Signs and Symptoms in Patients Surveyed by EWORS in Four Indonesian Sites, 2001-2004. Poster presentation at the International Conference on Emerging Infectious Diseases, Atlanta, GA, March 19-22, 2006.
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Blazes DL, Lescano AG, Corwin AL, Simanjutak CH, Mundaca CC, Larasati R, Glass JS. Correlation between signs, symptoms and disease syndromes, EWORS Indonesia 2001-2004. Poster presentation at the International Conference on Emerging Infectious Diseases, Atlanta, GA, March 19-22, 2006.
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Lescano AG, Simanjutak CH, Larasati R, Blazes DL, Glass JS, Corwin AL. Seasonal Variation in Selected Disease Syndromes and Implications for Outbreak Detection, EWORS Indonesia 2001-2004. Poster presentation at the International Conference on Emerging Infectious Diseases, Atlanta, GA, March 19-22, 2006.
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Lescano AG, Larasati R, Simanjutak CH, Blazes DL, Corwin AL, Glass JS. Variability of Retrospective Estimates of Disease Frequency and Influence of the Window Period. Results From Four Indonesian EWORS Sites, 2001-2004. Poster
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presentation at the International Conference on Emerging Infectious Diseases, Atlanta, GA, March 19-22, 2006. •
Lescano AG, Garcia HH, Gilman RH, Guezala MC, Tsang VCW, Gavidia CM, Rodriguez S, Moulton LH, Green JA, Taquiri C, Gonzalez AE and the Cysticercosis Working Group in Peru. Cysticercosis hotspots surrounding Taenia solium tapeworm carriers. Oral presentation at the 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Washington DC, December 2005.
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Lescano AG, Garcia HH, Gilman RH, Guezala MC, Tsang VCW, Rodriguez S, Moulton LH, Villaran MV, Montano SMm Gonzalez AE and the Cysticercosis Working Group in Peru. Human cysticercosis hotspots surrounding Taenia solium tapeworm carriers. Poster presentation at the 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Washington DC, December 2005.
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Konda KA, Klausner JD, Lescano AG, Leon S, Castillo R, Gadea N, Jones FR, Coates TJ, Caceres CF, and the NIMH Collaborative HIV/STI Prevention Trial Group. HIV and HSV-2 infections among men who have sex only with men in urban, coastal Peru. Poster presentation at the 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Washington DC, December 2005.
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Salmon-Mulanovich G, Konda KA, Lescano AG, Blazes DL. Frequent Needlesticks among Phlebotomists in a Peruvian Field Study. Poster presentation at the 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Washington DC, December 2005.
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Torres PA, Mundaca CC, Quispe J, Lescano AG, Blazes DL. Outbreak of Cyclosporiasis at a Naval Base in Ancon, Lima, Peru. Oral presentation at the 54th
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Annual Meeting of the American Society of Tropical Medicine and Hygiene, Washington DC, December 2005. •
Bustos JA, Rodriguez S, Jimenez J, Lescano AG, Moyano L, Gonzalvez G, Allan JC, Gonzalez AE, Gilman RH, Tsang VCW, Garcia HH, for the Cysticercosis Working Group in Peru. Coproantigen Detection for Early and Accurate Assessment of Taeniasis Treatment. Oral presentation at the 54th Annual Meeting of the American Society of Tropical Medicine and Hygiene,Washington DC, December 2005.
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Blazes DL, Gonzales J, Chretien JP, Lescano AG, Smoak B, Maguina C, Laughlin L. Age of verrucous lesions predicts Bartonella bacilliformis bacteremia: implications for man as the reservoir. Poster presentation at the 43 r meeting of the American Society of Infectious Diseases, San Francisco, October 2005
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Blazes DL, Acosta R, Lescano AG, Decker CF. Prevalence of and risk factors for syphilitic hepatitis among a cohort of patients in the Washington, DC Region between 2001 and 2004. Poster presentation at the 43rd meeting of the American Society of Infectious Diseases, San Francisco, October 2005
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Chretien JP, Blazes DL, Lescano AG, Smoak BL, Malone JL. Overseas Platforms for Microbial Threat Defense: A 5-Year Review of the DoD-GEIS OCONUS Laboratory Program. 8
Annual Force Health Protection Conference, Lousville, KY, August
2005 •
Konda KA, Munayco CV, Klausner JD, Pun MC, Lescano AG, Pajuelo J, Suarez L, Coates TJ, Caceres CF. Prevalence of infection with HIV, Herpes type 2, and syphilis in male partners of pregnant women using prenatal services in four coastal cities of
Peru. 16 Biennial Meeting of the International Society for Sexually Transmitted Diseases Research, Amsterdam, The Netherlands, July 2005. •
Konda KA, Fernandez P, Klausner JD, Lescano AG. Leon SR, Caceres CF, Coates TJ. Heterosexually identified, socially marginalized men who report recent sex with men in Peru. 16th Biennial Meeting of the International Society for Sexually Transmitted Diseases Research, Amsterdam, The Netherlands, July 2005.
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Lescano AG, Vargas J, Zurita S, Kelley PW, Blazes DL, Batsel TM. PHLIS in the new millennium: a cost-effective surveillance system for developing countries. American Society of Tropical Medicine and Hygiene, Miami, FL, November 2004.
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Cespedes M, Blair PJ, Sihuincha M, Lescano AG. Olson J, Vinetz J. Outbreak of Leptospirosis in Iquitos, Peru. American Society of Tropical Medicine and Hygiene, Miami, FL, November 2004.
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Lescano AG, Salmon G, Blazes DL, Pedroni E, Batsel TM. Outbreak Investigation and Response Training in the Americas. Experiences at NMRCD. The Third TEPHINET Global Scientific Conference, Beijing, China, November 2004
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Gadea N, Meza M, Leon S, Perez J, Lescano AG, Pajuelo J, Caceres C, Klausner JD, Coates TJ, Jones FR. Association between bacterial vaginosis and other sexually transmitted diseases among woung women in Peru. 42" Annual Meeting of the Infectious Diseases Society of America, Boston, MA, September 2004
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