T. Winston Vickers1,2, DVM, MPVM; Linda Munson3, DVM, PhD; Deana L. Clifford2,4, DVM, MPVM, PhD; David K. Garcelon1, MS; Julie King5, MS; Calvin Duncan5, BS; Walter M. Boyce2, DVM, PhD
1Institute for Wildlife Studies, Arcata, CA, USA; 2Wildlife Health Center, University of California, Davis, CA, USA; 3School of Veterinary Medicine, University of California, Davis, CA, USA; 4Wildlife Investigations Lab, California Department of Fish and Game, Rancho Cordova, CA, USA; 5Catalina Island Conservancy, Avalon, CA, USA
Read the Spanish translation: Alta Prevalencia de Cáncer del Canal Auditivo en las Zorras de las Islas Catalina, Amenazadas de Extinción (Urocyon littoralis catalinae)
Since 2001, an unusually high number of ceruminous gland carcinomas (CGC) and ceruminous gland adenomas (CGA) (collectively “tumors”) have been detected in endangered Santa Catalina (SCA) island foxes (Urocyon littoralis catalinae). CGC can have an aggressive clinical course with local invasion or metastasis, and both CGC and CGA can manifest as chronic disease characterized by severe otitis externa and/or fatal sepsis. To determine the prevalence and risk factors for tumors, 357 foxes on SCA, San Nicolas Island, and San Clemente Island were examined, and 156 foxes were biopsied for histopathology and sampled for ear mites, bacteria, viruses, and toxins. Tumors were found only in SCA foxes. Among foxes ≥4-year-old, 48% had tumors, 2/3 of which were CGC. The most significant condition associated with CGC was severe otitis externa with ceruminous gland hyperplasia, likely stimulated by ear mite infections. These lesions were more severe in SCA foxes than in foxes on the other islands, though ear mite prevalence approached 100% on all islands. No viruses were detected, and no bacterial infections or toxins were significantly associated with tumors. This study disclosed a nearly unprecedented level of cancerous and non-cancerous tumors in a wildlife population. Whether these tumors occur in SCA foxes because of genetic predisposition, or other factors such as ear mites, is under investigation. Treatment of 57 SCA foxes for ear mites resulted in absence of mites and reduced visible inflammation in 36 of 40 study animals recaptured at 6 months. Histopathology of pre- and post-treatment biopsies is underway.
The authors would like to thank the Morris Animal Foundation, Catalina Island Conservancy, Institute for Wildlife Studies, and U.S. Navy for their financial or logistical support of this study. We would also like to acknowledge and thank Brian Stacy, Bob Poppenga, Grace Lee, Susan Winston, Michael Puzzo, Megan Moriarty, Robyn Shea, Windee Evans, Darcee Guttilla, Brian Hudgens, Peter Sharpe, Steffani Jijon, Carlos de la Rosa, Francesca Ferrara, Dan Biteman, David Simmons, Andrew Bridges, and Grace Smith for their cooperation or assistance with the study.