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The musk rat (Ondatra zibethicus) as intermediate host of cestodes in the Netherlands
Veterinary Parasitology 117 (2003) 29–36
The musk rat (Ondatra zibethicus) as intermediate host of cestodes in the Netherlands Fred H.M. Borgsteede a,∗ , Joop H. Tibben a , Joke W.B. van der Giessen b a
Animal Sciences Group Wageningen UR, Division Infectious Diseases, P.O. Box 65, 8200 AB Lelystad, The Netherlands b Institute of Public Health and Environment RIVM, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
Received 11 March 2003; received in revised form 2 July 2003; accepted 19 July 2003
Abstract An investigation on the presence of larval cestodes in musk rats (Ondatra zibethicus) was carried out in two regions of the Netherlands (east Groningen and south Limburg) where in a earlier study foxes with Echinococcus multilocularis were found. A total of 1726 musk rats were dissected (1200 in Groningen, 526 in Limburg). Larval stages of Taenia taeniaeformis were most frequently found (total 44.8%: Groningen 42%, Limburg 51.3%), followed by T. martis (total 6.1%: Groningen 0.7%, Limburg 18.6%). Infections with T. crassiceps (total 0.3%: Groningen 0%, Limburg 1.0%), T. polyacantha (total 0.2%; Groningen 0.3%, Limburg 0%) and E. multilocularis (0.1%: Groningen 0.1%, Limburg 0%) were rare. Infections with T. taeniaeformis were more frequent in adults (71.8%) than in juveniles (34.2%). The same was found for T. martis: adults 15.3%, juveniles 2.5%. This difference was also reflected in the relation between weight of the animals and presence of infection. Heavier animals (>1000 g) were more often infected with T. taeniaeformis (74.1%) than animals less than 1000 g (34.8%). In musk rats weighing less than 500 g (n = 155) only 5.2% were infected, but above 1200 g, 82.6%. The highest number of T. taeniaeformis was 28, of T. martis 13, of T. crassiceps >1000 and of T. polyacantha 24. The E. multilocularis was in a very young stage, a few white spots in the liver. Although E. multilocularis infections were exceptional, it is expected that with a rise in the number of infected foxes in the Netherlands the number of infected musk rats will increase. © 2003 Elsevier B.V. All rights reserved. Keywords: Ondatra zibethicus; Musk rat; Echinococcus multilocularis; Taenia spp.; The Netherlands
∗ Corresponding author. Tel.: +31-320-238086; fax: +31-320-238050. E-mail address: [email protected] (F.H.M. Borgsteede).
0304-4017/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2003.07.015
30
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
1. Introduction There is an increasing number of papers on the prevalence of Echinococcus multilocularis in Europe outside the well-known endemic areas of Germany, Switzerland, Austria and France. E. multilocularis has recently been reported from Belgium (Losson et al., 1997), Czech Republic (Kolarova et al., 1996), Poland (Malczewski et al., 1995) and Slovak Republic (Dubinský et al., 1999). The number of countries where this is highly dangerous parasite can be found has increased. In Germany, positive foxes have been found in regions where the parasite was absent and in endemic areas higher infection levels among foxes have been observed (Daugschies, 1995; Eckert, 1996; Lucius and Bilger, 1995; Romig et al., 1999). In the Netherlands, E. multilocularis was not observed in an extensive survey of parasites of foxes (Borgsteede, 1984). The first report of E. multilocularis in the Netherlands came from Van der Giessen et al. (1999) who found 5 of 272 foxes positive. All foxes were shot close to the German border, two from the province of Groningen and three from the province of Limburg. Investigations in Asia showed that not only mice and voles, but also musk rats can serve as intermediate hosts (Arslanova, 1962; Bondareva et al., 1975). In Europe, Frank and Zeyhle (1981) found the first positive musk rats (8 of 437) in Baden-Würtemmberg, Germany. Musk rats are well known hosts of other larval cestodes, particularly of the larval stage of the cat tapeworm T. taeniaeformis (Eble, 1957; Friedland et al., 1985; Baumeister et al., 1997). In the Netherlands, there is a government organised, nation wide control campaign for musk rats, because these animals are undermining dikes which are used to protect the country against water overflow. The last 15 years more than 250,000 musk rats are caught per year all over the country. Therefore, it is relatively easy to collect these animals for parasitological studies. For the present study, the two localities where positive foxes were found, were chosen to investigate musk rats for the presence of larval E. multilocularis and other larval cestodes.
2. Materials and methods 2.1. Collection and dissection of the musk rats Professional musk rat catchers in the provinces of Groningen and Limburg were asked to collect freshly caught, undamaged rats in 1998 and 1999 in the regions where positive foxes had been found and to store them at −20 ◦ C with an identification label with the date and place of catch. Catches were located according to the quadrant system in use (so-called hourblocks of ca. 5 km × 5 km). Frozen musk rats were transported to Lelystad and thawed for examination. From each musk rat, the date and place of sampling, weight and sex was recorded. The age was determined as adult or subadult according to Pankakoski (1980) and Zygankow (1955). Data of the investigated rats are presented in Table 1.
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
31
Table 1 Province of origin, age and sex of the investigated musk rats (Ondatra zibethicus) Year
Province
1998 1998 1999 1999
Groningen Limburg Groningen Limburg
Total
Adult
Adult
Subadult
Subadult
73 55 91 48 267
Total
75 42 74 31
247 127 245 75
219 89 176 59
614 313 586 213
222
694
543
1726
2.2. Larval cestodes The pleural and peritoneal cavity of the musk rats was opened and searched for the presence of larval cestodes, either free in the lumen or attached to the internal organs or as cysts in the liver. The liver was also inspected for the presence of white spots. If these spots were found, they were removed, placed on a slide, cleared with chlorallactophenol and examined under a microscope. The liver was cut into thin slices to look for cysts that could not be detected at the surface. The larval cestodes were counted and identified to the species level (Verster, 1969).
3. Results Larval stages of five different cestode species were found. T. taeniaeformis as cysts in the liver, T. martis and T. polyacantha free in the peritoneal cavity, T. crassiceps free in the peritoneal and, in one musk rat, also in the pleural cavity and E. multilocularis as white spots in the liver. Details of the prevalence of T. taeniaeformis and T. martis according to the age and gender of the musk rats are presented in Table 2. For both worm species it was found that musk rats from Limburg were significantly more infected than those of Groningen (P < 0.05). Adults were more commonly infected than subadults (P < 0.01), but between sexes no significant difference could be demonstrated. Fig. 1 shows the relation of the weight of the musk rats and their infection with T. taeniaeformis. Heavier animals (>1000 g) had higher intensities of T. taeniaeformis (74.1%) than animals less than 1000 g (34.8%). In musk rats weighing less than 500 g (n = 155) only 5.2% was infected, but above 1200 g 82.6%. The number of cysts of T. taeniaeformis in the liver varied from 1 to 28. The frequency distribution is given in Fig. 2. The average number of cysts was 3.3. Adult musk rats had more significant cysts than subadults (3.8 vs. 3.0; P < 0.05). Musk rats from Limburg had significantly more cysts than musk rats from Groningen (3.8 vs. 3.1; P < 0.05). Between sexes no differences could be observed (3.4 vs. 3.2; N.S.). Taenia martis was more prevalent in Limburg. The highest number was 13, the average is 2.5. No difference in prevalence and number of worms was found between adults and subadults, nor between sexes. Taenia crassiceps was found in the peritoneal cavity of five musk rats, all from Limburg. Two rats had >1000 larval cysts, two had around 100 and one had 50. In one of the musk rats with >1000 cysts, they were found in the peritoneal and the pleural cavity.
32
Musk rat age/ gender
Species
Groningen 1998 N
Male, adult Female, adult Total adult Male, subadult Female, subadult Total subadult Overall total
T. taeniaeformis 73 T. martis T. taeniaeformis 75 T. martis T. taeniaeformis 148 T. martis
Limburg 1999
Pos (%)
N
Pos (%)
49 (67.1) 91 61 (67.0) 2 (2.7) 1 (1.1) 48 (64.0) 74 50 (67.6) 1 (1.3) 0 97 (65.5) 165 111 (67.3) 3 (2.0) 1 (0.6)
T. taeniaeformis 247 103 (41.7) 245 64 (26.1) T. martis 0 4 (1.6) T. taeniaeformis 219 80 (36.5) 176 49 (27.8) T. martis 0 0 T. taeniaeformis 466 183 (39.3) 421 113 (26.8) T. martis 0 4 (1.0)
Total Groningen
1998
N
N
Pos (%)
164 110 (67.1) 3 (1.8) 149 98 (65.8) 1 (0.7) 313 208 (66.5) 4 (1.3)
55 42 97
492 167 (33.9) 127 4 (0.8) 395 129 (32.7) 89 0 887 296 (33.4) 216 4 (0.5)
Overall total 1999
Pos (%) 45 (81.8) 26 (47.3) 33 (78.6) 19 (45.2) 78 (80.4) 45 (46.4)
N 48 31 79
44 (34.6) 75 11 (8.7) 33 (37.1) 59 10 (11.2) 77 (35.6) 134 21 (9.7)
Total Limburg Pos (%)
N
Pos (%)
38 (79.2) 103 83 (80.6) 13 (27.1) 39 (37.9) 27 (87.1) 73 60 (82.2) 13 (41.9) 32 (43.8) 65 (82.3) 176 143 (81.3) 26 (32.9) 71 (40.3)
N
Pos (%)
267 193 (72.3) 42 (15.7) 222 158 (71.2) 33 (14.9) 489 351 (71.8) 75 (15.3)
30 (40.0) 202 74 (36.6) 694 241 (34.7) 5 (6.7) 16 (7.9) 20 (2.9) 20 (33.9) 148 53 (35.8) 543 182 (33.5) 1 (1.7) 11 (7.4) 11 (2.0) 50 (37.1) 350 127 (36.3) 1237 423 (34.2) 6 (4.5) 27 (7.7) 31 (2.5)
T. taeniaeformis 614 280 (45.6) 586 224 (38.2) 1200 504 (42.0) 313 155 (49.5) 213 115 (54.0) 526 270 (51.3) 1726 774 (44.8) T. martis 3 (0.5) 5 (0.9) 8 (0.7) 66 (21.1) 32 (15.0) 98 (18.6) 106 (6.1)
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
Table 2 Prevalence of T. taeniaeformis and T. martis in musk rats in Groningen and Limburg, the Netherlands
33
1451-1500
1301-1350
1151-1200
1001-1050
851-900
701-750
551-600
401-450
251-300
100 90 80 70 60 50 40 30 20 10 0 100-150
% positive
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
weight (g) Fig. 1. Frequency distribution of musk rats from Groningen and Limburg, the Netherlands, infected with larval stages of T. taeniaeformis (n = 774) according to their weight.
Taenia polyacantha was present in three musk rats, all from Groningen. The number varied from 6 to 24. Only one musk rat from Groningen, caught in 1999, was positive for E. multilocularis. A few small white spots in the liver were caused by this species, as could be shown under the microscope on the basis of the shape and size of the hooks. All other white spots, frequently found in the liver of other musk rats, proved to be caused by calcium deposits.
350
300
no. musk rats
250
200
150
100
50
0 1 2 3
4 5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 no. of cysts
Fig. 2. Frequency distribution of the number of cysts of T. taeniaeformis in musk rats in Groningen and Limburg, the Netherlands (n = 774).
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F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
4. Discussion The main reason for this study was to investigate the presence of E. multilocularis in musk rats. This worm was recently found in the Netherlands (Van der Giessen et al., 1999) and the question was if this worm had already established in the intermediate host as well and if the musk rat could be used as a tracer animal for the demonstration of the presence of this tapeworm. Musk rats are easily available for a survey, because they are caught in huge numbers, particularly in regions which are rich of water. However, only one musk rat was positive in our study and the infection was in a very young stage. A possible explanation for this low prevalence might be that the level of infection in foxes was low. Studies from Germany, where a much higher percentage of foxes is infected, showed variable prevalences in musk rats. In Lower Saxony, Seegers et al. (1995) found 34 positive animals of 418 (8.1%) and Baumeister et al. (1997) 41 of 991 (4.1%). In Freiburg, 5% of 1101 musk rats were infected (Ewald, 1990), while Frank and Zeyhle (1981) found 8 of 437 (1.8%) musk rats with E. multilocularis. Also in France, Boussinesq et al. (1986) demonstrated the presence of E. multilocularis in 1 of 8 musk rats. Unfortunately, the results in the literature do not permit correlation between prevalence in musk rats and in foxes, although Ewald (1990) determined a very high correlation factor (R = 0.9). In the study of Van der Giessen et al. (1999) 5 of 272 foxes were positive for E. multilocularis. More recent data show an increase to a base line prevalence of 9.4% in Groningen (Van der Giessen and Borgsteede, 2002). This means that, if a correlation factor of 0.9 is correct, in 1999 in Groningen ca. 50 musk rats should be positive. A possible explanation of the difference could be that the base line prevalence in 1999 was lower than in 2001 and that at low prevalence levels in the fox, the correlation factor is also lower. Besides this, it has been shown that even within one region local differences can be great. If, as shown by Baumeister et al. (1997) in a certain region 33% of the musk rats is infected, foxes need to consume only 3–4 musk rats to become infected. However, the consumption of musk rats by foxes will depend on a lot of factors, including the presence of other prey animals. One also has to keep in mind that the German habit to strip a caught musk rat for the skin and leave the carcass in the field is an easy way for a fox to get his food (Frank and Zeyhle, 1981). This habit is not known in the Netherlands. Although E. multilocularis was extremely rare in this study, this cannot be said of the larval stage of the cat tapeworm T. taeniaeformis. This worm was found in 44.8% of the investigated rats. In adult musk rats the prevalence is much higher. Obviously, there is an increasing risk to become infected when animals grow older. Our result is not different from that of German studies: Frank and Zeyhle (1981): 48.1%; Friedland et al. (1985): 44.2% and Baumeister et al. (1997): 42.3%. These authors also noticed the higher prevalence in adults. Also the frequency distribution of cysts in the liver was comparable. Unfortunately, no data about the prevalence of T. taeniaeformis in Dutch cats are available, but according to this study, it should be high. T. martis was more prevalent in Limburg. The obvious reason is the much higher number of Martes foina in Limburg compared with Groningen. In German studies there was also a clear relationship between the presence of T. martis in musk rats and the presence of suitable final hosts. Frank and Zeyhle (1981) found T. martis in 207 out of 437 musk rats (47.4%), while Baumeister et al. (1997) found only 3.4% in Lower Saxony, an area with
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35
less martens. In the most northern part of Germany, Sleswick-Holstein, the parasite was absent (Friedland et al., 1985). The frequency distribution of T. martis larvae in the musk rat in our study did not differ from the results of Frank and Zeyhle (1981). T. crassiceps was absent in Groningen, but present in five musk rats in Limburg (1.0%). Also in other studies, this species is rather rare (Frank and Zeyhle, 1981: 0.9%; Baumeister et al., 1997: 2.7%). This Taenia species differs from the others, because there is an asexual multiplication in the intermediate host. We have not counted all cysts, but Friedland et al. (1985) counted 11,083! T. polyacantha was absent in Limburg, but present in three musk rats in Groningen (0.3%). Frank and Zeyhle (1981) found an infection percentage of 7.3 and Baumeister et al. (1997) of 0.4. Confusion with T. martis is hardly possible if the number of hooks is counted (≥55 for T. polyacantha and ≤34 for T. martis). Recent observations in the Netherlands (Van der Giessen and Borgsteede, 2002) indicate an increase of E. multilocularis in foxes in Groningen. The present situation in Limburg and in other parts of the Netherlands is the subject of present studies. The role of musk rats as indicator animals for the prevalence of E. multilocularis in foxes has to be analysed in regions in which the worm has already established and in new invaded regions. Musk rats could serve as excellent survey animals, because they are—different from other rodents such as voles—easy to get in great numbers, section can be done in a very short time and, compared with foxes, they are much safer to work with, because there is no infection risk.
Acknowledgements The authors wish to acknowledge the technical assistance of Tineke Wassenaar and, above all, the excellent cooperation of the Muskusrattenbestrijdingsdienst (Organisation for the control of musk rats) in the Netherlands, particularly Jan Folkers and his crew in Groningen and Harry Hutschemakers in Limburg. This study was partly financed by the Ministry of Agriculture, Nature Reserve and Fisheries.
References Arslanova, A.K., 1962. An enzootic focus of alveolar hydatidosis in the Alma-Ata region. Med. Parazytol. Parazyt. Boleznei 31, 88–91 (in Russian). Baumeister, S., Pohlmeyer, K., Kuschfeldt, S., Stoye, M., 1997. Zur Prävalenz von Echinococcus multilocularis und anderen Metazestoden des Bisams (Ondatra zibethicus LINK 1795) in Niedersachsen. Dtsch. tierärztl. Wschr. 104, 448–452. Bondareva, V.J., Boev, S.N., Tazieva, Z.K., Sokolova, J.B., 1975. Echinococcus multilocularis in Ondatra zibethicus, Vulpes vulpes, Felis libyca, Vulpes fulvus, Mustela altaica, rodents, cat and dog in the Pribalkhashye Kazakh SSR. Alma-Ata, Akad. Nauk. Kazakh. SSR. Vopr. Prirodn. Ochagov. Bolznei 7, 97 (in Russian). Borgsteede, F.H.M., 1984. Helminth parasites of wild foxes (Vulpes vulpes) in The Netherlands. Z. Parasitenkd. 70, 281–285. Boussinesq, M., Bresson, S., Liange, M., Houin, R., 1986. Un nouvel hˆote intermédiaire naturel d’ (Echinococcus multilocularis en France. Le rat musqué (Ondatra zibethicus L.). Ann. Parasit. Hum. Comp. 61, 431–434. Daugschies, A., 1995. Aktuelles zur Epidemiologie und Bekämpfung des Fuchsbandwurmes, Echinococcus multilocularis, in Deutschland. Dtsch. tierärztl. Wschr. 102, 306–310.
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Dubinský, P., Svobodovbá, V., Turˇceková, L., Literák, I., Mart´ınek, K., Reiterová, K., Koláˇrová, L., Klimeš, J., Mrl´ık, V., 1999. Echinococcus multilocularis in Slovak Republic the first record in foxes Vulpes vulpes. Helminthologia 36, 105–110. Eble, H., 1957. Befall der Bisamratte durch Cysticercus fasciolaris im Gebiet der DDR. Wiss. Z. Univ. Halle, Math.-Nat. 4, 159–166. Eckert, J., 1996. Der “gefärliche Fuchsbandwurm” (Echinococcus multilocularis) und die alveoläre Echinokokkose des Menschen in Mitteleuropa. Berl. Münch. tierärztl. Wschr. 109, 202–210. Ewald, D., 1990. Die Verbreitung des Fuchsbandwurmes Echinococcus multilocularis bei Fuchs (Vulpes vulpes) und Bisam (Ondatra zibethicus) im regierbezirk Freiburg. Mitt. Bad. Landesverb. Naturkunde u. Naturschutz 15, 81–99. Frank, B., Zeyhle, E., 1981. Echinokokken- und andere Bandwurmlarven im Bisam (Ondatra zibethicus). Nachrichtenbl. Deutsch. Pflanzenschutzd. 33, 166–170. Friedland, T., Steiner, B., Böckeler, W., 1985. Prävalenz der Cysticercose bei Bisams (Bisam (Ondatra zibethica L.)) in Schleswig-Holstein. Z. Jagdwiss. 31, 134–139. Kolarova, L., Pavlasek, I., Chalupsky, J., 1996. Echinococcus multilocularis (Leuckart, 1863) in the Czech Republic. Helminthologia 33, 59–65. Losson, B., Mignon, B., Brochier, B., Baudien, B., Pastoret, P.P., 1997. Echinococcus multilocularis infection in the red fox (Vulpes vulpes) in the province of Luxembourg (Belgium): results of a survey conducted between 1993 and 1995. Ann. Med. Vet. 141, 149–155. Lucius, R., Bilger, B., 1995. Echinococcus multilocularis in Germany: increased awareness or spreading of a parasite? Parasitol. Today 11, 430–433. Malczewski, A., Rocki, B., Ramisz, A., Eckert, J., 1995. Echinococcus multilocularis (Cestoda), the causative agent of alveolar echinococcus in human beings: first recors in Poland. J. Parasitol. 81, 318–321. Pankakoski, E., 1980. An improved method for age determination in the muskrat Ondatra zibethica (L.). Ann. Zool. Fenn. 17, 113–121. Romig, T., Bilger, B., Mackenstedt, U., 1999. Zur aktuellen Verbreitung und Epidemiologie von Echinococcus multilocularis. Dtsch. tierärztl. Wschr. 106, 352–357. Seegers, G., Baumeister, S., Pohlmeyer, K., Stoye, M., 1995. Echinococcus multilocularis- Metazestoden bei Bisamratten in Niedersachsen. Dtsch. tierärztl. Wschr. 102, 256. Van der Giessen, J.W.B., Borgsteede, F.H.M., 2002. Echinococcus multilocularis: de kleine lintworm van de vos met mogelijk grote gevolgen voor de mens. Tijdschr. Diergeneesk. 127, 318–321. Van der Giessen, J.W.B., Rombout, Y.B., Franchimont, J.H., Limper, L.P., Homan, W.L., 1999. Detection of Echinococcus multilocularis in foxes in The Netherlands. Vet. Parasitol. 82, 49–57. Verster, A., 1969. A taxonomic revision of the genus Taenia Linnaeus, 1758. Onderstepoort J. Vet. Res. 36, 3–58. Zygankow, D.S., 1955. A method for age determination and longivety of the musk rat Fiber zibethicus L. Zool. Zh. (Moskva) 34, 640–651 (in Russian).
The musk rat (Ondatra zibethicus) as intermediate host of cestodes in the Netherlands Fred H.M. Borgsteede a,∗ , Joop H. Tibben a , Joke W.B. van der Giessen b a
Animal Sciences Group Wageningen UR, Division Infectious Diseases, P.O. Box 65, 8200 AB Lelystad, The Netherlands b Institute of Public Health and Environment RIVM, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
Received 11 March 2003; received in revised form 2 July 2003; accepted 19 July 2003
Abstract An investigation on the presence of larval cestodes in musk rats (Ondatra zibethicus) was carried out in two regions of the Netherlands (east Groningen and south Limburg) where in a earlier study foxes with Echinococcus multilocularis were found. A total of 1726 musk rats were dissected (1200 in Groningen, 526 in Limburg). Larval stages of Taenia taeniaeformis were most frequently found (total 44.8%: Groningen 42%, Limburg 51.3%), followed by T. martis (total 6.1%: Groningen 0.7%, Limburg 18.6%). Infections with T. crassiceps (total 0.3%: Groningen 0%, Limburg 1.0%), T. polyacantha (total 0.2%; Groningen 0.3%, Limburg 0%) and E. multilocularis (0.1%: Groningen 0.1%, Limburg 0%) were rare. Infections with T. taeniaeformis were more frequent in adults (71.8%) than in juveniles (34.2%). The same was found for T. martis: adults 15.3%, juveniles 2.5%. This difference was also reflected in the relation between weight of the animals and presence of infection. Heavier animals (>1000 g) were more often infected with T. taeniaeformis (74.1%) than animals less than 1000 g (34.8%). In musk rats weighing less than 500 g (n = 155) only 5.2% were infected, but above 1200 g, 82.6%. The highest number of T. taeniaeformis was 28, of T. martis 13, of T. crassiceps >1000 and of T. polyacantha 24. The E. multilocularis was in a very young stage, a few white spots in the liver. Although E. multilocularis infections were exceptional, it is expected that with a rise in the number of infected foxes in the Netherlands the number of infected musk rats will increase. © 2003 Elsevier B.V. All rights reserved. Keywords: Ondatra zibethicus; Musk rat; Echinococcus multilocularis; Taenia spp.; The Netherlands
∗ Corresponding author. Tel.: +31-320-238086; fax: +31-320-238050. E-mail address: [email protected] (F.H.M. Borgsteede).
0304-4017/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2003.07.015
30
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
1. Introduction There is an increasing number of papers on the prevalence of Echinococcus multilocularis in Europe outside the well-known endemic areas of Germany, Switzerland, Austria and France. E. multilocularis has recently been reported from Belgium (Losson et al., 1997), Czech Republic (Kolarova et al., 1996), Poland (Malczewski et al., 1995) and Slovak Republic (Dubinský et al., 1999). The number of countries where this is highly dangerous parasite can be found has increased. In Germany, positive foxes have been found in regions where the parasite was absent and in endemic areas higher infection levels among foxes have been observed (Daugschies, 1995; Eckert, 1996; Lucius and Bilger, 1995; Romig et al., 1999). In the Netherlands, E. multilocularis was not observed in an extensive survey of parasites of foxes (Borgsteede, 1984). The first report of E. multilocularis in the Netherlands came from Van der Giessen et al. (1999) who found 5 of 272 foxes positive. All foxes were shot close to the German border, two from the province of Groningen and three from the province of Limburg. Investigations in Asia showed that not only mice and voles, but also musk rats can serve as intermediate hosts (Arslanova, 1962; Bondareva et al., 1975). In Europe, Frank and Zeyhle (1981) found the first positive musk rats (8 of 437) in Baden-Würtemmberg, Germany. Musk rats are well known hosts of other larval cestodes, particularly of the larval stage of the cat tapeworm T. taeniaeformis (Eble, 1957; Friedland et al., 1985; Baumeister et al., 1997). In the Netherlands, there is a government organised, nation wide control campaign for musk rats, because these animals are undermining dikes which are used to protect the country against water overflow. The last 15 years more than 250,000 musk rats are caught per year all over the country. Therefore, it is relatively easy to collect these animals for parasitological studies. For the present study, the two localities where positive foxes were found, were chosen to investigate musk rats for the presence of larval E. multilocularis and other larval cestodes.
2. Materials and methods 2.1. Collection and dissection of the musk rats Professional musk rat catchers in the provinces of Groningen and Limburg were asked to collect freshly caught, undamaged rats in 1998 and 1999 in the regions where positive foxes had been found and to store them at −20 ◦ C with an identification label with the date and place of catch. Catches were located according to the quadrant system in use (so-called hourblocks of ca. 5 km × 5 km). Frozen musk rats were transported to Lelystad and thawed for examination. From each musk rat, the date and place of sampling, weight and sex was recorded. The age was determined as adult or subadult according to Pankakoski (1980) and Zygankow (1955). Data of the investigated rats are presented in Table 1.
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
31
Table 1 Province of origin, age and sex of the investigated musk rats (Ondatra zibethicus) Year
Province
1998 1998 1999 1999
Groningen Limburg Groningen Limburg
Total
Adult
Adult
Subadult
Subadult
73 55 91 48 267
Total
75 42 74 31
247 127 245 75
219 89 176 59
614 313 586 213
222
694
543
1726
2.2. Larval cestodes The pleural and peritoneal cavity of the musk rats was opened and searched for the presence of larval cestodes, either free in the lumen or attached to the internal organs or as cysts in the liver. The liver was also inspected for the presence of white spots. If these spots were found, they were removed, placed on a slide, cleared with chlorallactophenol and examined under a microscope. The liver was cut into thin slices to look for cysts that could not be detected at the surface. The larval cestodes were counted and identified to the species level (Verster, 1969).
3. Results Larval stages of five different cestode species were found. T. taeniaeformis as cysts in the liver, T. martis and T. polyacantha free in the peritoneal cavity, T. crassiceps free in the peritoneal and, in one musk rat, also in the pleural cavity and E. multilocularis as white spots in the liver. Details of the prevalence of T. taeniaeformis and T. martis according to the age and gender of the musk rats are presented in Table 2. For both worm species it was found that musk rats from Limburg were significantly more infected than those of Groningen (P < 0.05). Adults were more commonly infected than subadults (P < 0.01), but between sexes no significant difference could be demonstrated. Fig. 1 shows the relation of the weight of the musk rats and their infection with T. taeniaeformis. Heavier animals (>1000 g) had higher intensities of T. taeniaeformis (74.1%) than animals less than 1000 g (34.8%). In musk rats weighing less than 500 g (n = 155) only 5.2% was infected, but above 1200 g 82.6%. The number of cysts of T. taeniaeformis in the liver varied from 1 to 28. The frequency distribution is given in Fig. 2. The average number of cysts was 3.3. Adult musk rats had more significant cysts than subadults (3.8 vs. 3.0; P < 0.05). Musk rats from Limburg had significantly more cysts than musk rats from Groningen (3.8 vs. 3.1; P < 0.05). Between sexes no differences could be observed (3.4 vs. 3.2; N.S.). Taenia martis was more prevalent in Limburg. The highest number was 13, the average is 2.5. No difference in prevalence and number of worms was found between adults and subadults, nor between sexes. Taenia crassiceps was found in the peritoneal cavity of five musk rats, all from Limburg. Two rats had >1000 larval cysts, two had around 100 and one had 50. In one of the musk rats with >1000 cysts, they were found in the peritoneal and the pleural cavity.
32
Musk rat age/ gender
Species
Groningen 1998 N
Male, adult Female, adult Total adult Male, subadult Female, subadult Total subadult Overall total
T. taeniaeformis 73 T. martis T. taeniaeformis 75 T. martis T. taeniaeformis 148 T. martis
Limburg 1999
Pos (%)
N
Pos (%)
49 (67.1) 91 61 (67.0) 2 (2.7) 1 (1.1) 48 (64.0) 74 50 (67.6) 1 (1.3) 0 97 (65.5) 165 111 (67.3) 3 (2.0) 1 (0.6)
T. taeniaeformis 247 103 (41.7) 245 64 (26.1) T. martis 0 4 (1.6) T. taeniaeformis 219 80 (36.5) 176 49 (27.8) T. martis 0 0 T. taeniaeformis 466 183 (39.3) 421 113 (26.8) T. martis 0 4 (1.0)
Total Groningen
1998
N
N
Pos (%)
164 110 (67.1) 3 (1.8) 149 98 (65.8) 1 (0.7) 313 208 (66.5) 4 (1.3)
55 42 97
492 167 (33.9) 127 4 (0.8) 395 129 (32.7) 89 0 887 296 (33.4) 216 4 (0.5)
Overall total 1999
Pos (%) 45 (81.8) 26 (47.3) 33 (78.6) 19 (45.2) 78 (80.4) 45 (46.4)
N 48 31 79
44 (34.6) 75 11 (8.7) 33 (37.1) 59 10 (11.2) 77 (35.6) 134 21 (9.7)
Total Limburg Pos (%)
N
Pos (%)
38 (79.2) 103 83 (80.6) 13 (27.1) 39 (37.9) 27 (87.1) 73 60 (82.2) 13 (41.9) 32 (43.8) 65 (82.3) 176 143 (81.3) 26 (32.9) 71 (40.3)
N
Pos (%)
267 193 (72.3) 42 (15.7) 222 158 (71.2) 33 (14.9) 489 351 (71.8) 75 (15.3)
30 (40.0) 202 74 (36.6) 694 241 (34.7) 5 (6.7) 16 (7.9) 20 (2.9) 20 (33.9) 148 53 (35.8) 543 182 (33.5) 1 (1.7) 11 (7.4) 11 (2.0) 50 (37.1) 350 127 (36.3) 1237 423 (34.2) 6 (4.5) 27 (7.7) 31 (2.5)
T. taeniaeformis 614 280 (45.6) 586 224 (38.2) 1200 504 (42.0) 313 155 (49.5) 213 115 (54.0) 526 270 (51.3) 1726 774 (44.8) T. martis 3 (0.5) 5 (0.9) 8 (0.7) 66 (21.1) 32 (15.0) 98 (18.6) 106 (6.1)
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
Table 2 Prevalence of T. taeniaeformis and T. martis in musk rats in Groningen and Limburg, the Netherlands
33
1451-1500
1301-1350
1151-1200
1001-1050
851-900
701-750
551-600
401-450
251-300
100 90 80 70 60 50 40 30 20 10 0 100-150
% positive
F.H.M. Borgsteede et al. / Veterinary Parasitology 117 (2003) 29–36
weight (g) Fig. 1. Frequency distribution of musk rats from Groningen and Limburg, the Netherlands, infected with larval stages of T. taeniaeformis (n = 774) according to their weight.
Taenia polyacantha was present in three musk rats, all from Groningen. The number varied from 6 to 24. Only one musk rat from Groningen, caught in 1999, was positive for E. multilocularis. A few small white spots in the liver were caused by this species, as could be shown under the microscope on the basis of the shape and size of the hooks. All other white spots, frequently found in the liver of other musk rats, proved to be caused by calcium deposits.
350
300
no. musk rats
250
200
150
100
50
0 1 2 3
4 5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 no. of cysts
Fig. 2. Frequency distribution of the number of cysts of T. taeniaeformis in musk rats in Groningen and Limburg, the Netherlands (n = 774).
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4. Discussion The main reason for this study was to investigate the presence of E. multilocularis in musk rats. This worm was recently found in the Netherlands (Van der Giessen et al., 1999) and the question was if this worm had already established in the intermediate host as well and if the musk rat could be used as a tracer animal for the demonstration of the presence of this tapeworm. Musk rats are easily available for a survey, because they are caught in huge numbers, particularly in regions which are rich of water. However, only one musk rat was positive in our study and the infection was in a very young stage. A possible explanation for this low prevalence might be that the level of infection in foxes was low. Studies from Germany, where a much higher percentage of foxes is infected, showed variable prevalences in musk rats. In Lower Saxony, Seegers et al. (1995) found 34 positive animals of 418 (8.1%) and Baumeister et al. (1997) 41 of 991 (4.1%). In Freiburg, 5% of 1101 musk rats were infected (Ewald, 1990), while Frank and Zeyhle (1981) found 8 of 437 (1.8%) musk rats with E. multilocularis. Also in France, Boussinesq et al. (1986) demonstrated the presence of E. multilocularis in 1 of 8 musk rats. Unfortunately, the results in the literature do not permit correlation between prevalence in musk rats and in foxes, although Ewald (1990) determined a very high correlation factor (R = 0.9). In the study of Van der Giessen et al. (1999) 5 of 272 foxes were positive for E. multilocularis. More recent data show an increase to a base line prevalence of 9.4% in Groningen (Van der Giessen and Borgsteede, 2002). This means that, if a correlation factor of 0.9 is correct, in 1999 in Groningen ca. 50 musk rats should be positive. A possible explanation of the difference could be that the base line prevalence in 1999 was lower than in 2001 and that at low prevalence levels in the fox, the correlation factor is also lower. Besides this, it has been shown that even within one region local differences can be great. If, as shown by Baumeister et al. (1997) in a certain region 33% of the musk rats is infected, foxes need to consume only 3–4 musk rats to become infected. However, the consumption of musk rats by foxes will depend on a lot of factors, including the presence of other prey animals. One also has to keep in mind that the German habit to strip a caught musk rat for the skin and leave the carcass in the field is an easy way for a fox to get his food (Frank and Zeyhle, 1981). This habit is not known in the Netherlands. Although E. multilocularis was extremely rare in this study, this cannot be said of the larval stage of the cat tapeworm T. taeniaeformis. This worm was found in 44.8% of the investigated rats. In adult musk rats the prevalence is much higher. Obviously, there is an increasing risk to become infected when animals grow older. Our result is not different from that of German studies: Frank and Zeyhle (1981): 48.1%; Friedland et al. (1985): 44.2% and Baumeister et al. (1997): 42.3%. These authors also noticed the higher prevalence in adults. Also the frequency distribution of cysts in the liver was comparable. Unfortunately, no data about the prevalence of T. taeniaeformis in Dutch cats are available, but according to this study, it should be high. T. martis was more prevalent in Limburg. The obvious reason is the much higher number of Martes foina in Limburg compared with Groningen. In German studies there was also a clear relationship between the presence of T. martis in musk rats and the presence of suitable final hosts. Frank and Zeyhle (1981) found T. martis in 207 out of 437 musk rats (47.4%), while Baumeister et al. (1997) found only 3.4% in Lower Saxony, an area with
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35
less martens. In the most northern part of Germany, Sleswick-Holstein, the parasite was absent (Friedland et al., 1985). The frequency distribution of T. martis larvae in the musk rat in our study did not differ from the results of Frank and Zeyhle (1981). T. crassiceps was absent in Groningen, but present in five musk rats in Limburg (1.0%). Also in other studies, this species is rather rare (Frank and Zeyhle, 1981: 0.9%; Baumeister et al., 1997: 2.7%). This Taenia species differs from the others, because there is an asexual multiplication in the intermediate host. We have not counted all cysts, but Friedland et al. (1985) counted 11,083! T. polyacantha was absent in Limburg, but present in three musk rats in Groningen (0.3%). Frank and Zeyhle (1981) found an infection percentage of 7.3 and Baumeister et al. (1997) of 0.4. Confusion with T. martis is hardly possible if the number of hooks is counted (≥55 for T. polyacantha and ≤34 for T. martis). Recent observations in the Netherlands (Van der Giessen and Borgsteede, 2002) indicate an increase of E. multilocularis in foxes in Groningen. The present situation in Limburg and in other parts of the Netherlands is the subject of present studies. The role of musk rats as indicator animals for the prevalence of E. multilocularis in foxes has to be analysed in regions in which the worm has already established and in new invaded regions. Musk rats could serve as excellent survey animals, because they are—different from other rodents such as voles—easy to get in great numbers, section can be done in a very short time and, compared with foxes, they are much safer to work with, because there is no infection risk.
Acknowledgements The authors wish to acknowledge the technical assistance of Tineke Wassenaar and, above all, the excellent cooperation of the Muskusrattenbestrijdingsdienst (Organisation for the control of musk rats) in the Netherlands, particularly Jan Folkers and his crew in Groningen and Harry Hutschemakers in Limburg. This study was partly financed by the Ministry of Agriculture, Nature Reserve and Fisheries.
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