Trop Anim Health Prod DOI 10.1007/s11250-010-9698-8
ORIGINAL RESEARCH
Seroepidemiology of leptospirosis in livestock in Trinidad Sharianne M. Suepaul & Christine V. Carrington & Mervyn Campbell & Gustave Borde & Abiodun Adewale Adesiyun
Accepted: 26 September 2010 # Springer Science+Business Media B.V. 2010
Abstract A study was conducted to determine the seroprevalence of leptospirosis and infecting serovars across livestock (cattle, sheep, goats, and pigs) in Trinidad using the microscopic agglutination test with an international panel of 23 serovars. Of a total of 590 cattle tested, 21.5% were seropositive with agglutinations to 13 of the 23 antigens used in the panel. Icterohaemorrhagiae (9.3%), Sejroe (4.1%), Ballum (4.1%), and Autumnalis (1.9%) were the predominant serogroups detected in the cattle sampled (n=590). Of 222 sheep tested, 5.0% were seropositive with agglutinations to five serovars belonging to two serogroups. These serogroups were Autumnalis at 2.7%, and Icterohaemorrhagiae at 2.3% of all sheep tested (n=222). Of a total of 180 goats tested, 3.3% were seropositive, all agglutinating to the Icterohaemorrhagiae serogroup, 1.7% to serovar Copenhageni, 1.1% to serovar Mankarso, and 0.6% to serovar Icterohaemorrhagiae. Among pigs (n=200), 5.0% were seropositive for five serovars belonging to three serogroups. These serogroups were Icterohaemorrhagiae at 2.5%, Australis at 2%, and Ballum at 0.5%. Overall, age and sex of animals were not significantly associated with leptospirosis with the exception of cattle where age was a significant factor for seropositivity. It was concluded that for livestock, leptospirosis may be an important zoonotic and economic disease, particularly in the case of cattle. It is S. M. Suepaul : M. Campbell : G. Borde : A. A. Adesiyun (*) School of Veterinary Medicine, Faculty of Medical Sciences, The University of the West Indies, Trinidad, West Indies, Trinidad and Tobago e-mail:
[email protected] C. V. Carrington Department of Preclinical Sciences, Faculty of Medical Sciences, The University of the West Indies, St. Augustine, Trinidad and Tobago
imperative that the impact of leptospirosis on abortion, stillbirths, and decreased milk production in livestock in the country be assessed. Keywords Livestock . Leptospira . Seroprevalence . Microscopic agglutination test Abbreviations MAT Microscopic agglutination test ELISA Enzyme-linked immunosorbent assay
Introduction Leptospirosis is a zoonosis of global importance (Bharti et al. 2003). There has been an increase in the prevalence of the disease in recent times such that it is now referred to as a re-emerging disease (Meites et al. 2004). Animals such as rodents, dogs, cattle, sheep, goats, and pigs act as reservoirs of infection for certain serovars of Leptospira, shedding the organism in the urine and thus contaminating the environment (World Health Organization 2003). The organisms can exist in water and soil as detected in samples taken from rice fields, water channels, and rivers; these act as sources of infection for humans (Issazadeh et al. 2008). While reservoir hosts may not display clinical signs when infected with particular serovars, infection of humans with these same serovars may result in illness and disease (Babudieri 2006; Everard and Green 1976). A basic knowledge of serovars and their maintenance hosts is required to understand the epidemiology of leptospirosis in a region. Though distinct variations in maintenance hosts and the serovars they carry can occur throughout the world (Levett 2004), the general pattern is
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for serogroups Hardjobovis, Pomona, and Grippotyphosa to be recoverable from cattle. In sheep and goats however, serovars Pomona, Grippotyphosa, Hardjo, and Bratislava are common while in pigs, the prevalent infecting serovars are Pomona, Tarassovi, Grippotyphosa, Bratislava, Sejroe, Canicola, Autumnalis, and Icterohaemorrhagiae (Faine 1994). The diagnosis of leptospirosis is based on two principles which include the actual isolation of the leptospiral organisms and the detection of anti-leptospiral antibodies. Isolation by culture is very time-consuming and depends on the presence of live Leptospira and their ability to grow on media provided, thus serological testing is a more widely used method (Aslantas and Ozdemir 2005). The detection of anti-leptospiral antibodies can be done using tests such as the microscopic agglutination test (MAT) and enzymelinked immunosorbent assay (ELISA). The MAT is the “gold standard” test for diagnosing leptospirosis and is the most widely used method for detecting both Leptospira IgG and IgM antibodies in animal sera. The sensitivity and specificity of the MAT reported in a recent study by Dassanayake et al. (2009) were 91.94% and 73.77%, respectively. This test can be used qualitatively and quantitatively to detect the infecting serovar and titer (World Health Organization 2003), but it requires the propagation of live leptospiral strains to be used as antigens for a hazardous and time-consuming process in which the interpretation of the results can be subjective. Cross-reactions within and between serogroups can occur with this test. ELISAs on the other hand tend to be genus specific and in some cases have been shown to be 100% sensitive and 96% specific (Adler et al. 1980; Vitale et al. 2004), however kits may be expensive to purchase. Livestock, with acute leptospirosis, show various clinical signs including abortions, stillbirths, decreased milk production, infertility, and death. Mastitis can also occur and there may be a disturbance in milk flow and quality, during which period leptospires may also be found in the milk. Chronic leptospirosis also occurs in livestock (Radostits et al. 2000) when the animal becomes a carrier and the leptospires grow and reside in the renal tubules for days or years and are occasionally shed into the urine. It is very difficult to provide a proportion of animals infected with leptospirosis because they may not exhibit clinical signs or excrete the leptospires in the urine at the time of conducting the surveys. Bovine leptospirosis causes enormous economic losses. The seroprevalence, as detected by the MAT, varies from 36.2% to 49.5% of cattle herds in Spain (Alonso-Andioberry et al. 2001), 46.9% in Rio de Janeiro (Lilenbaum and Souza 2003), 20% in Martinique (Levett et al. 1996), 10.3% in Mexico (Leon et al. 2008) to 8.8% in Turkey
(Aslantas and Ozdemir 2005). Sheep and goats, when compared to other species are considered less susceptible to leptospirosis (Pugh 2002), for reasons which are unexplained. However, leptospirosis can cause abortions in these animals (Leon-Vizcaino et al. 1987). In a study conducted at a sheep-only abattoir in New Zealand, 5.7% of the sheep tested positive for anti-leptospiral antibodies (Dorjee et al. 2008). In Vietnam, a seroprevalence of 36.7% for leptospirosis was reported in goats (Ngan and Tien 2001) while in pigs tested in Thailand 10% were positive by the MAT with 55% being positive for serovar Grippotyphosa (Niwetpathomwat et al. 2006) both studies using the MAT. A study conducted in 1985 in Trinidad and Grenada serologically detected Leptospira antibodies in cattle (92%) and pigs (52%) in Trinidad, as well as antibodies in sheep (35%), goats (25%) in Grenada; with the predominant serogroups encountered being Icterohaemorrhagiae, Autumnalis, Panama, and Hebdomadis (Everard et al. 1985). With the exception of a study by Adesiyun et al. (2009), which reported a seroprevalence of 14.6% in water buffalo, there are no recently published studies on the prevalence of leptospirosis in livestock in Trinidad. With respect to the wider Caribbean, Levett et al. in 1996 conducted a serological survey of 13 islands of the Lesser Antilles and found an overall seroprevalence rate of 5.6% in livestock tested with cattle and goats displaying the majority of agglutinations at 7.2% each, followed by sheep at 1.7%. For cattle, the highest prevalence was detected in Martinique (20%), while for goats the highest prevalence was detected in St. Vincent (23%) (Levett et al. 1996). Since leptospirosis is an important zoonosis that can inflict economic losses in livestock (particularly in developing countries) and given that livestock may serve as maintenance hosts, we sought to determine the seroprevalence of leptospirosis in cattle, goats, sheep, and pigs across Trinidad. We also determined the frequency and geographical distribution of serovars of Leptospira spp. in the country.
Materials and methods Area of study The Caribbean island of Trinidad is the southernmost island in the archipelago. The Trinidad and Tobago Meteorological Office at Piarco reports high long-term 30-year averages for humidity and rainfall at 82.2% and 1,869.8 mm, respectively. It rains year round, however most of the rainfall occurs during the rainy season (June to December).
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Determination of sample size and strategy for sampling animals The livestock sampled in this study included cattle, sheep, goats, and pigs. Accurate data on seroprevalences in the individual populations of these animals in Trinidad is unavailable, so a reported prevalence (Pexp) of 44% for all livestock (Everard et al. 1985) was used to calculate the minimum required sample size. The latter was determined using the equation: n ¼ 1:962 Pexp 1 Pexp =d 2 (Thrusfield 2007), with a precision rate (d) of 4%. A minimum required sample size (n) of 592 was therefore determined. We aimed for the final sample size to contain animals of each species in the estimated proportions at which they exist in Trinidad, i.e., approximately 40% cattle and 20% each for sheep, goats, and pigs. A list of farms was compiled from the information obtained from the Ministry of Agriculture, Land and Marine Resources and the Animal Health Assistants who routinely assist government veterinarians in providing services to the livestock farmers. For cattle, based on the compiled list, systematic sampling of farms was performed by choosing every third farm on the list and at the farms cattle were sampled opportunistically. If the selected farmers refused to participate in the study, the next farm listed was sampled. Sheep, goat and pig farms, which were fewer in the country, were sampled in an opportunistic manner. The minimal sample number was surpassed due to the fact that sampling conditions could not be predicted. Some farms contained a larger number of animals than reported, while other farms had a combination of species, which were sampled opportunistically. It should be noted that vaccination of livestock against leptospirosis is not practiced in Trinidad, but there are few instances where private farms chose to do so. Vaccinated animals were not included in this study. Demographic data were obtained through the administration of questionnaires to farmers. For analysis, cattle were divided into young (
