Ear tumors found in Island foxes

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Until recently, endangered foxes on California’s Catalina Island were suffering from one of the highest prevalence of tumors ever documented in a wildlife population, UC Davis scientists have found. But treatment of ear mites appears to be helping the wild animals recover.

Until recently, endangered foxes on California’s Catalina Island were suffering from one of the highest prevalence of tumors ever documented in a wildlife population, UC Davis scientists have found. But treatment of ear mites appears to be helping the wild animals recover.

Roughly half of adult foxes examined between 2001 and 2008 had tumors in their ears, with about two-thirds of those malignant, according to a UC Davis study published this month in the journal PLOS ONE. More than 98 percent of the foxes were also infected with ear mites.  These mites appear to be a predisposing factor for ear tumors in the Santa Catalina Island fox.

Luckily for the foxes, the story doesn’t stop there. “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,” said Winston Vickers, lead author of the study and an associate veterinarian with the UC Davis Wildlife Health Center at the UC Davis School of Veterinary Medicine.

A complementary study, also led by UC Davis and published in PLOS ONE today, found that treatments with acaracide, a chemical agent used to kill ear mites in dogs and cats, reduced the prevalence of ear mite infection from 98 percent to 10 percent among foxes at the end of the six-month trial.

“It’s rare to have a success story,” said the ear mite study’s lead author, Megan Moriarty, a student with the UC Davis School of Veterinary Medicine when the study began and currently a staff research associate at the UC Davis Wildlife Health Center.

Santa Catalina Island foxes are managed by the Catalina Island Conservancy. In 2009, when the mite treatment study began, the conservancy added acaracide to the preventative treatments they administer annual to the foxes.  Since then, the overall prevalence of ear mites has dramatically declined, as have the rates of tissue masses in the ear canals, suggesting reduced tumor presence. Conservancy biologists have also documented a cascade effect on the foxes’ offspring, since most young foxes get the ear mites from their parents.

Both studies received funding or other support from the Morris Animal Foundation, Institute for Wildlife Studies, Catalina Island Conservancy, U.S. Navy and The Nature Conservancy.

Co-authoring institutions for the prevalence study included Institute for Wildlife Studies, UC Davis School of Veterinary Medicine, California Department of Fish and Wildlife, Catalina Island Conservancy, and UC San Diego.

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