Until recently, endangered foxes on California’s Catalina Island were suffering from one of the highest prevalences of tumors ever documented in a wildlife population, according to UC Davis scientists. 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 in late December in the journal PLOS ONE.
More than 98 percent of the foxes were also infected with ear mites.
Working closely with researchers from the Institute for Wildlife Studies and Catalina Island Conservancy, the scientists conducted one of the few studies to estimate disease prevalence in an entire free-living wildlife population.
A complementary study, also led by UC Davis and published in PLOS ONE 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 treated foxes at the end of the six-month trial. Ear canal inflammation and other signs of developing ear tumors also dropped.
“It’s rare to have a success story,” said the ear mite study’s lead author, Megan Moriarty, a staff research associate at the UC Davis Wildlife Health Center. “It was interesting to see such striking results over a relatively short time period.”
In 2009, when the mite treatment study began, the Catalina Island Conservancy added acaracide to the variety of preventative treatments they administer to the foxes each year.
The conservancy confirms that, in the years since, the overall prevalence of ear mites has dramatically declined in the areas they normally catch and treat foxes, as have the rates of tissue masses in the ear canals, suggesting reduced tumor presence.
“The annual prophylactic acaracide treatment has greatly improved the overall condition of the foxes’ ear canals,” said Julie King, the conservancy’s director of Conservation and Wildlife management and co-author of both studies. “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.”
Conservancy biologists have also documented a cascade effect on the foxes’ offspring, since most young foxes get the ear mites 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 said.
The studies also pose new questions such as, ear mites infect other Channel Island foxes, but those foxes don’t develop ear canal tumors. Winston Vickers, lead author of the prevalence study and an associate veterinarian with the UC Davis Wildlife Health Center at the UC Davis School of Veterinary Medicine is preparing to research possible genetic reasons.