Investigation of Epidemiologic and Nutritional Factors Associated with a Global Epizootic of Transitional Cell Carcinoma in Fishing Cats (Prionailurus viverrinus)
Transitional cell carcinoma (TCC) of the urinary bladder has been previously reported in fishing cats (Prionailurus viverrinus) maintained in North American zoos,1,3 but the pathogenesis and prevalence of TCC are unknown. In this study, our objectives were to: (1) investigate the prevalence of TCC in captive fishing cats in North America and internationally, (2) evaluate risk factors possibly associated with TCC occurrence in North American zoos, and (3) begin assessing nutritional parameters in fishing cats to explore a possible link between diet and TCC. A combination of email survey of zoo veterinarians and pathologic surveillance identified 29 confirmed cases of TCC in fishing cats housed in North American zoos since 1995, representing ∼35% of all fishing cats (>5 years of age) that died during this time period. Notably, TCC was diagnosed in three imported founders originating from three different fishing cat range countries (Thailand, Cambodia, Sri Lanka). Additional TCC cases (n=13) were observed in fishing cats housed in European and Australian zoos. Epidemiologic analysis of data from the Fishing Cat International Studbook determined that genetic relatedness, geographic region, number of transfers between zoos, and gender were not (p>0.05) correlative factors for TCC. Nutritional analysis of serum samples (n=58) from 42 fishing cats (including 19 TCC cases) in 17 North American zoos found increased (p=0.032) saturated fatty acid and increased (p=0.048) palmitic acid and decreased (p=0.022) gamma-linolenic acid (GLA) concentrations in cats affected with TCC versus cats without TCC. Vitamins A and E, and antioxidant levels did not differ (p>0.05). These findings indicate that TCC is a global disease concern, occurring at an epizootic level in captive fishing cats with no identifiable demographic risk factors. Because fishing cat diets in North American zoos are comprised primarily of beef with very little fish (∼20%, on average), we suspect that TCC occurrence may be influenced by dietary factors. Beef-based diets are substantially higher than fish in saturated fatty acids, a dietary component correlated with TCC in humans2 and found in the present study to be higher in fishing cats with TCC. Similarly, levels of GLA, a tumoricidal fatty acid, were lower in TCC-affected cats. These observations suggest that increasing fish composition of zoo diets to more closely mimic diets of wild fishing cats may be warranted as a preventative measure to reduce TCC-related morbidity and mortality.
The authors are grateful to the North American zoos (Alexandria Zoological Park, Audubon Zoo, Brookfield Zoo, Cheyenne Mountain Zoo, Cincinnati Zoo and Botanical Garden, Cleveland Metroparks Zoo, Exotic Feline Breeding Compound, Louisville Zoological Garden, Memphis Zoo, Mill Mountain Zoo, Minnesota Zoological Garden, Oklahoma City Zoological Park, Omaha’s Henry Doorly Zoo and Aquarium, Point Defiance Zoo and Aquarium, Potter Park Zoological Gardens, Riverbanks Zoo and Garden, San Antonio Zoological Gardens and Aquarium, San Diego Zoo, San Francisco Zoological Gardens, Smoky Mountain Zoological Park) that provided fishing cat blood samples for this study. We also thank the Fishing Cat Red Program coordinator (Jessica Kinzer, Riverbanks Zoo), the Fishing Cat EEP coordinator and International Studbook Keeper (Milada Rehakova, Decin Zoo) and the Australasian Regional Veterinary Officer (Andrea Reiss, Zoo and Aquarium Association) for providing studbook and TCC data, and Tom Vennard at Procter and Gamble Pet Care for assistance with nutritional analysis. This study was funded, in part, by the Procter and Gamble Wildlife Conservation Scholars program.
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3. Sutherland-Smith M, Harvey C, Campbell M, et al. Transitional cell carcinomas in four fishing cats (Prionailurus viverrinus). J Zoo Wildl Med. 2004;35(3):370-380.