Paul-Murphy J, Work T, Hunter D, et al. Serological survey and ... 780 Blanshard Street, Victoria, British Columbia V8VJX4. Can Vet J Volume 37, April 1996.
CROSS CANADA DISEASE REPORT RAPPORT DES MALADIES DIAGNOSTIQUEES AU CANADA
British Columbia Serological evidence of toxoplasma infection in cougars on Vancouver Island, British Columbia n spring 1995, the largest recorded outbreak of human toxoplasmosis was identified in the greater Victoria region on southern Vancouver Island, British Columbia. Epidemiologic studies implicated the community water supply as the likely source of Toxoplasma gondii oocysts for the outbreak (1). During the hypothesized exposure period, cougars (Felis concolor) and domestic cats were observed within the Victoria watershed. Felids are the only animals known to shed T. gondii oocysts, which are the form of the parasite that would be involved in water-borne transmission (2). Although antibodies to T. gondii have been detected in cougars in California (3), it was unknown if cougars on southern Vancouver Island were infected with the parasite. Serum was collected from 5 cougars (identified as A,B,C,D,E) captured during winter 1994 in Northwest Bay, approximately 100 km north of the Victoria region. Evidence of antibodies specifically binding to T. gondii was sought by 2 techniques: a commercially available hemagglutination-based screening test (Toxo-IHA, Carter-Wallace Inc, Cranbury, New Jersey, USA) and an indirect immunohistochemical test. For hemagglutination testing, a pool of sera was made using serum from cougars B,C,D, and E, combined in equal parts and tested at a dilution of 1/64, according to the test manufacturer's directions. The rationale for pooling the samples was that each was severely hemolysed, and as the test is not designed to be conducted on hemolysed sera, the pooled assay was considered as a screening test only. The serum from cougar A was not grossly hemolysed and was tested individually. The pooled sample and A's sample were both strongly positive in this assay. Each sample was then tested individually for antibodies binding to T. gondii, using an indirect immunohistochemical test on formalin-fixed, paraffin-embedded, raccoon tissues containing T. gondii cysts. The staining method was essentially as previously described (4). The titer of antibodies to T. gondii in the cougar sera was the last dilution of each serum yielding a specific staining of tissue cysts. The results of the indirect immunohistochemical testing confirmed the presence of antibodies specific to T. gondii in these cougars, thus establishing past exposure to the parasite (Table 1). Since we do not know the magnitude of titers in cougars that correlate with recent versus past exposure to T. gondii,
Table 1. Results of indirect immunohistochemical testing for antibodies specific for Toxoplasma gondii in 5 cougars from southern Vancouver Island Estimated age
Cougar
Sex
A B C D E
Female Female Female Female Male
(y) 6-8 4-6 6-8 9-12 7-10
Titer
>1/160 1/40 .1/160 .1/160 1/40
parasites in the 1995 outbreak in Victoria. Four of 7 domestic cats captured in the Victoria watershed near the end of the outbreak were also serologically positive for antibodies to T. gondii (1). Wild felids were implicated as the source of parasite in another water-borne outbreak of human toxoplasmosis. In this outbreak, involving American soldiers in Panama, "jungle cat" feces were thought to have contaminated a surface water source used by the soldiers (2). However, in neither the Victoria nor the Panama outbreak was there direct evidence to identify a specific animal species as the source of infection. Further laboratory and epidemiological studies are being undertaken in the Victoria watershed to elucidate the relationship between wildlife and the risk to human health of water-borne protozoal infection.
References 1. British Columbia Toxoplasmosis Team. Outbreak of toxoplasmosis associated with municipal drinking water - British Columbia. Can Commun Dis Rep 1995; 21: (18): 1-2. 2. Smith JL. Documented outbreaks of toxoplasmosis: Transmission of Toxoplasma gondii to humans. J Food Protect 1993; 56: 630-639. 3. Paul-Murphy J, Work T, Hunter D, et al. Serological survey and serum biochemical reference ranges of free-ranging mountain lions (Felis concolor) in California. J Wild Dis 1994; 30: 205-215. 4. Haines DM, Chelack BJ. Technical considerations for developing enzyme immunohistochemical staining procedures on fornalin-fixed paraffin-embedded tissues for diagnostic pathology. J Vet Diagn Invest 1991: 3: 101-112.
Craig Stephen, Centre for Coastal Health, Department of Health Care and Epidemiology, University of British Columbia, Vancouver, British Columbia V6T JZ3; Deborah Haines, Department of Veterinary Microbiology, Trent Bollinger, Canadian Cooperative Wildlife Health Centre, Western College of Veterinary Medicine, University ofSaskatchewan, Saskatoon, Saskatchewan S7N OWO; no comment can be made as to the time of their Knut Atkinson, Wildlife Branch, Ministry of Environexposures. Although the results demonstrate that ment, Lands and Parks, 2569 Kentworth Road, Nanaimo, cougars could reasonably be considered as potential British Columbia V9T4P7; Helen Schwantje, Wildlife sources of infectious oocysts on southern Vancouver Branch, Ministry of Environment, Lands, and Parks, Island, they do not identify cougars as the source of 780 Blanshard Street, Victoria, British Columbia V8V JX4. Can Vet J Volume 37, April 1996
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