Liver fluke (Opisthorchiidae) findings in red foxes (Vulpes vulpes) in the eastern part of the Federal State Brandenburg, Germany â a contribution to the ...
Parasitol Res (1999) 85: 142 ± 146
Ó Springer-Verlag 1999
ORIGINAL PAPER
Rolf Schuster á JoÈrg Bonin Christoph Staubach á Rolf Heidrich
Liver ¯uke (Opisthorchiidae) ®ndings in red foxes (Vulpes vulpes) in the eastern part of the Federal State Brandenburg, Germany ± a contribution to the epidemiology of opisthorchiidosis Received: 20 May 1998 / Accepted: 18 June 1998
Abstract Parasitological examination of 677 livers from red foxes shot in connection with a rabies control programme were carried out in the eastern districts of the Federal State Brandenburg/Germany in 1996. Of the foxes, 32.5% were positive for opisthorchiid ¯ukes. Metorchis bilis, the most frequently occurring ¯uke was found in 28.1% of foxes with numbers between 1 and 185. Opisthorchis felineus was found in 6.7% of fox livers. A maximum of 169 specimens was removed from one animal. Pseudamphistomum truncatum was present in only 2 foxes. The percentage of positive foxes in different districts varied between 15.8 and 43.3%. Signi®cant dierences in ¯uke prevalence were found between districts with a high share of surface water compared with a district with a low percentage of surface water. No sex-dependent dierences in opisthorchiid prevalence were established.
Introduction Opisthorchis felineus (Rivolta, 1884) as a foodborne transmitted parasite and known as a zoonotic agent is widely distributed in several parts of the former U.S.S.R. According to estimates, 2 million people are infected and each year 40,000±95,000 new cases of human opisthorchiidosis occur (WHO 1995) in the former R. Schuster (&) á J. Bonin Institute of Parasitology and Tropical Veterinary Medicine, Freie UniversitaÈt Berlin, KoÈnigsweg 67, D-14163 Berlin, Germany Fax: +49-30-81082323 C. Staubach Federal Research Centre for Virus Diseases of Animals, Institute for Epidemiology, Seestrasse 55, D-16868 Wusterhausen/Dosse, Germany R. Heidrich State Veterinary and Food Control Institute, Postfach 469, D-15204 Frankfurt/Oder, Germany
U.S.S.R alone. Pseudamphistomum truncatum and members of the genus Metorchis are also likely to be potential zoonotic agents (Skrjabin and Sulc 1929; Maclean et al. 1996). Since ingestion of raw cyprinid ®sh is uncommon for the indigenous human population, human opisthorchiidosis is rarely diagnosed in Germany and the last cases of indigenous infections occurred more than 10 years ago (SaÈnger et al. 1991). However, due to the growing number of naturalized people with dierent eating habits coming from the former U.S.S.R., cases of human opisthorchiidosis are considered likely for the future. For this reason, it is necessary to have data on the occurrence of these ¯ukes in a larger territory. Recently, Hering-Hagenbeck and Schuster (1996) indicated that at least one natural focus of O. felineus exists in the eastern part of the Federal State Brandenburg with cats as de®nitive hosts, and Bithynia leachi and several cyprinid ®sh as ®rst and second intermediate hosts, respectively. The other ¯uke identi®ed in their study was Metorchis bilis (Braun, 1790). Using this work as a basis, we decided to map the occurrence of mammalian opisthorchiids in the whole area. This article presents the liver ¯uke situation in foxes in eastern Brandenburg.
Materials and methods Area under investigation Eastern Brandenburg, with a territory of 9,071.42 km2, consists of the following ®ve administrative districts: Uckermark (UM), Barnim (BAR), MaÈrkisch-Oderland (MOL), Oder-Spree (LOS) and the town of Frankfurt an der Oder (FF) (Fig. 1). The surface of the area under investigation developed during the ice age and is characterized by terminal morains and glacial valleys. The system of surface water bodies in eastern Brandenburg (Fig. 2) consists of the rivers Oder, Spree, and branches of the Old Oder, all of which ¯ow from south to north, the Oder-Spree canal and the Oder-Havel canal, linking the river Oder in the east with Berlin and the western parts of Germany, and a large number of lakes concentrated in the north and the south of the area under
143
Fig. 1 Administrative division of the Federal State Brandenburg investigation. The average percentage of surface water bodies in the examined districts varied between 2.5 and 5.2% (Table 1). Parasitological examination Of 1,473 foxes sent to the regional State Veterinary and Food Control Institute in Frankfurt/Oder in connection with a rabies control programme between March and December 1996, 677 (45.96%) were included in this investigation. Livers packed in plastic bags and stored at )18 °C were kept at room temperature overnight 1 day prior to examination. Gall bladders and bile ducts of the liver were examined seperately. For this procedure, the gall bladders were transferred into a Petri dish and opened by scissors. After the mucosa had been washed in 50 ml normal saline, all ¯uid was put into a glass for sedimentation for at least 10 min. When no ¯ukes were present, the sediment was examined under a microscope (magni®cation ´100) for ¯uke eggs. Liver lobules were sliced into 1-cm slices and put into normal saline in a large Petri dish. By taking these slices between two ®ngers, ¯ukes were squeezed out of the bile ducts. After removal of remnants, the supernatant was poured o and ¯ukes were counted and identi®ed. The individual origin of foxes, sex, age and the date of hunting were taken from the journal of the institute. Data analysis For data analysis, all results were put into an Excel data sheet (Microsoft Excel, version 5.0). To map the origin of the foxes and the distribution of infected animals, the ocial key numbers of municipalities of the Federal State Brandenburg (Anonymous 1995a) were used. Maps were generated using the geographical mapping software ARCVIEW for Windows, version 3.0 a (Environmental Systems Research Institute, Redlands, Calif.). The lower and upper limits for 95% con®dence intervals (CI) were calculated using the statistic programme Bias 6.01. The ®gures for the fox hunting bag per district, the surface area of the district, surface water shares and the size of hunting grounds were taken from the Statistical Yearbook of the Federal State Brandenburg (Anonymous 1995b).
Fig. 2 The system of surface water bodies in eastern Brandenburg (upper arrow Oder-Havel canal, lower arrow Oder-Spree canal)
Results Of 677 foxes examined, 220 (32.49%) were positive for liver ¯ukes (Table 2). M. bilis was the most frequent representative. This ¯uke species occurred in 190 (28.1%) animals. The number of M. bilis ranged between 1 and 185. In most cases, low numbers of ¯ukes were removed. Thus, 140 foxes harboured less than 10 ¯ukes. In 26 animals, the infection intensity ranged between 10 and 19, and only 24 foxes had more than 20 ¯ukes of this genus. M. bilis occurred in all ®ve districts (Table 2) and showed the highest prevalence of 39.2% in the Oder-Spree district. O. felineus was found in 45 (6.65%) foxes examined. The highest prevalence of 10.13% was again established in the Oder-Spree district (Table 2). Although low-level infections were predominant, the maximum number of ¯ukes found in one fox was 169. Two single specimens of P. truncatum were found in two foxes, one originating from Frankfurt a.d.
144 Table 1 Characterization of the area under investigation
District
Barnim MaÈrkisch Oderland Oder Spree Uckermark Frankfurt/Oder
Table 2 Prevalence of opisthorchiids in red foxes in eastern Brandenburg. Liver ¯ukes include ®ndings of opisthorchiid eggs in gall bladder sediments
District
Surface waters (%)
Hunting grounds (%)
Fox hunting bag 1994
1995
BAR MOL
1,494 2,128
5.2 2.5
79 84
2,147 2,278
2,203 3,455
LOS UM FF
2,242 3,058 147
3.8 4.9 3.5
83 73 57
1,877 3,302 173
Not reported 4,748 278
Total
9,071
4.1
79
9,777
10,684
Number of foxes examined
BAR
92
MOL
162
LOS
217
UM
185
FF
19
Total
Territory (km2)
677
Oder and the other from the Oder-Spree district (Table 2). In 17 animals (2.5%), no ¯ukes but only opisthorchiid eggs were present in gall bladder sediments. In all, 672 foxes included in this examination were classi®ed as adults. Of the ®ve juvenile foxes necropsied, two were infected with liver ¯ukes. The ratio of female (n 305) to male (n 386) foxes examined was 1:1.2. No sex-dependent dierences in ¯uke prevalence were detected for M. bilis, O. felineus or the total number of infected animals. P. truncatum was found only in two male foxes (Table 3). Figures 3 and 4 show the distribution of municipalities from which foxes with liver ¯ukes originated. Positive municipalities for both M. bilis and O. felineus were concentrated around the Oder-Spree canal and the river Spree in the Oder Spree district and the Oder-Havel canal in the Barnim district. The area bordering the river Oder appears to oer good conditions only for M. bilis.
Foxes positive for
prevalence (%)
Con®dence Intervals Lower limit
Upper limit
M. bilis O. felineus P. truncatum Liver ¯ukes M. bilis O. felineus P. truncatum Liver ¯ukes M. bilis O. felineus P. truncatum Liver ¯ukes M. bilis O. felineus P. truncatum Liver ¯ukes M. bilis O. felineus P. truncatum Liver ¯ukes
25.0 7.6 0 30.4 14.8 4.9 0 19.1 39.2 10.1 0.5 43.3 29.7 4.3 0 34.6 15.8 0 5.3 15.8
16.5 3.1 0.0 21.2 9.7 2.2 0.0 13.4 36.6 6.4 0.02 36.6 23.2 1.9 0.0 27.7 3.4 0.0 0.1 3.4
35.1 15.0 3.2 40.9 21.2 9.5 1.8 26.0 46.0 14.9 2.5 50.2 39.9 8.3 1.6 41.9 39.6 8.7 1.1 36.2
M. bilis O. felineus P. truncatum Liver ¯ukes
28.1 6.7 0.3 32.5
24.7 4.9 0.03 28.9
31.6 8.7 1.1 36.2
Of 23 municipalities examined here, 13 were positive for M. bilis while O. felineus was found in only 2.
Discussion Current investigations con®rmed the results of Saar (1957), SchoÈel (1991) and Schuster et al. (1997) that mammalian opisthorchiids in Germany are much more widely distributed than had previously been assumed. The red fox may not be the best indicator species for opisthorchiid distribution but this host species was chosen since no other possible ®nal host was available in large enough quantities over the whole area under investigation. Moreover, foxes were used because of their low migration behaviour in areas of low population density. According to Goretzki et al. (1997), 65% of marked foxes were shot within a radius of 5 km from their litter den and only 4% migrated up to 25±30 km. Similar data are published by Behrend (1955). There-
145 Table 3 Sex associated prevalence of liver ¯uke infection in foxes (values in parentheses are 95% con®dence limits) Sex
Number of foxes examined
Number of foxes positive for liver ¯ukes O. felineus %
n
%
n
%
n
%
31.25 (26.5, 36.3) 33.44 (28.2, 39.0) (75)
25
6.79 (4.4, 9.8) 6.22 (3.8, 9.6) (25)
102
27.7 (23.2, 32.6) 28.19 (23.2, 33.6) (50)
2
0.54 (0.06, 1.9) 0 (0.0, 0.9) (0)
6.64 (4.9, 8.7)
190
28.06 (24.7, 31.1)
2
368
115
Female
305
102
Total
P. truncatum
n Male
Unknown
M. bilis
4
3
677
220
32.49 (28.9, 36.2)
19 1 45
86 2
0 0
0.29 (0.04, 1.1)
Fig. 3 Occurrence of M. bilis in municipalities in eastern Brandenburg
Fig. 4 Occurrence of O. felineus in municipalities in eastern Brandenburg
fore, it can be assumed that the place of bagging in most cases is close to the place where liver ¯uke infection had taken place. Analyses of stomach contents showed that foxes are not specialized on any particular diet and are food generalists (Goretzki and Paustian 1982; Goretzki 1996). However, voles seemed to be the preferred fox food (Behrend 1955; Lutz 1978). In biotopes with low vole
population densities or in periods when voles are not available, foxes have to search for alternative food sources. These can consist of ®sh, especially in areas with a high percentage of surface water. Since the fox is not a good ®sher, it mainly feeds on dead ®sh or catches ®sh in the spring during the spawning period in shallow waters. These characteristics might explain dierences in opisthorchiid prevalences in various districts.
146
Foxes of the MaÈrkisch-Oderland district with the lowest percentage of surface waters showed the lowest liver ¯uke prevalence. In contrast, foxes originating from the Oder-Spree district with a similar area and percentage of hunting grounds but with a higher share of surface waters were twice as often infected with opisthorchiids. A similar situation was found in the Uckermark district. Although the water share in this district was even larger, the percentage of slow-running waters oering the best conditions for Bithynia snails as the ®rst intermediate hosts was lower. This fact could explain with the prevalence of liver ¯ukes did not reach the ®gures of the Oder-Spree district. The proportion of female and male specimens in a normal fox population is about 1:1.2 to 1:1.5 and each fox pair gives birth to an average of 5.5 puppies (Goretzki and Paustian 1982; Goretzki et al, 1997). Thus, the number of foxes rises by more than 300% in spring. But conditions of constant hunting claim onethird and a second third of the fox population dies due to diseases such as rabies, distemper, scabies and others, as well as in trac accidents. The remaining third survives to the next spring. Age analyses of fox bags showed that 75% of foxes do not reach their second year (Pfeier 1996; Goretzki et al. 1997). Thus, the low number of liver ¯ukes per animal found in our investigations may be explained by the young age of adult foxes and the fact that the main infection period is probably the spring. M. bilis was the most frequent liver ¯uke found in foxes. This ¯uke, which often occurs in the older sources under the synonym M. albidus (Braun, 1892), infects mammals as well as ®sh-eating birds (Razmaskin 1978; Sonin 1986). The reason for the frequent occurrence of M. bilis is that it uses Bithynia tentaculata, a widely distributed snail, as ®rst intermediate host. B. leachi, the ®rst intermediate host of O. felineus, in contrast, is a rarely occurring snail species. However, due to the linked systems of rivers and canals in the region under investigation, which allows ®sh migration, Opisthorchis infections can appear even in biotopes where B. leachi is absent. Little is known about the life cycle and host preference of P. truncatum. Findings of single ¯ukes of this species in only two foxes suggest that the fox may not be the main de®nitive host. Otherwise it is dicult to understand how its life cycle can be maintained. According to Zablockij (1967), B. tentaculata serves as ®rst and a variety of cyprinid ®sh as second intermediate hosts. The seal (Phoca vitulina), which showed a prevalence of 47%, appeared to be the main ®nal host. More than 100,000 specimens were found in one animal. Other mammals examined in the Volga delta positive for
P. truncatum were wolf, dog, raccoon dog, fox, cat and mink.
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