Endangered Santa Catalina Island Foxes: Ear Mite Treatment Reduces Cancerous Ear Tumors

Endangered foxes living on California's Santa Catalina Island have been found suffering from painful ear tumors, most of which are malignant. Now, however, researchers from the University of California Davis discovered using a common treatment for ear mites in dogs and cats may help many of the wild animals recover.

"We established a high prevalence of both tumors and ear mites, and hypothesized that there was something we could potentially do about it, which now appears to be significantly helping this population," Winston Vickers, an associate veterinarian with the UC-Davis Wildlife Health Center, explained in a news release.

The Santa Catalina Island fox is one of six subspecies native to the Channel Islands off the coast of Southern California. These relatively small foxes weigh only four to six pounds, but are the island's largest terrestrial predator. In 1999 a widespread epidemic killed off 90 percent of the foxes living on the island, leaving only 150 that were subsequently federally listed as endangered species. Since then, the population has rebounded to an estimated 1,717 foxes.

For their study, researchers tested the effectiveness of a chemical agent known as acaracide, with is used to kill ear mites in dogs and cats. Following a six-month medical trial, they discovered acaracide dramatically reduced the prevalence of an ear mite infection -- from 98 to 10 percent -- in treated foxes. Additionally, ear canal inflammation and other signs of tumors subsided. The study began in 2009, when UC Davis researchers added acaracide to the variety of preventative treatments administered to the foxes annually. (Scroll to read more...)

"The annual prophylactic acaracide treatment has greatly improved the overall condition of the foxes' ear canals," Julie King, co-author and director of Conservation and Wildlife Management at the Catalina Island Conservancy, said in the university's release. "Within just a few months post treatment, the presence of wax, infection, inflammation, and pigmentation virtually disappear. We have also noted an apparent reduction in the number of tumors observed, despite the fact that the absence of wax and other obstructions has made them easier to detect."

In addition to adult fox recovery, researchers also found that fewer offspring were infected with ear mites, which they would have gotten from their parents. "Prior to treatment in 2009, approximately 90 percent of all pups handled had ear mites, whereas by 2015, mites were detected in only 15 percent of new pups." King added.

The next step is assessing the long-term side effects of this tumor treatment, and to explore why Santa Catalina Island foxes are predisposed with ear tumors, while their Channel Island counterparts are not.

"It's rare to have a success story," Megan Moriarty, lead author of the study and currently a staff research associate at the UC Davis Wildlife Health Center who conducted the study as a student in UC Davis' School of Veterinary Medicine, said in the release. "It was interesting to see such striking results over a relatively short time period."

Their study was recently published in the journal PLOS ONE.

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