Ear Tumors Decreased in Catalina Island Foxes

The good news keeps coming for Channel Island foxes. Research published in the scientific journal PLoS ONE highlights the successful treatment of a serious cancer threat in the Santa Catalina Island fox.

Catalina Island foxes suffered a catastrophic decline following the introduction of Canine Distemper Virus in the late 1990s. As their population began to recover a new challenge threatened their survival: cancer. Fatal cancerous tumors, which developed in the ear canal, were discovered in a high percentage of the small surviving Catalina population.

FIF first reported on this threat in 2006 and 2007 (mysterious cancer). A new research paper details that between 2001 and 2008 nearly half of all adult Catalina Island foxes were found to have nodule-like tumors present in their ear canals and approximately two-thirds of these tumors were cancerous.

In the search to unravel the cause, it was discovered that nearly all island foxes with the tumors were also infected with ear mites. Veterinarians from UC Davis and biologists with the Catalina Island Conservancy and the Institute for Wildlife Studies hypothesized that treating the ear mites might reduce the irritation in infested foxes and therefore reduce inflammation. If the ear mites could be controlled or eliminated perhaps the progression to disease could be reduced.

Catalina Island fox receiving health check

Data collected during annual island fox counting and health checks determined the prevalence of the cancer (Ceruminous gland carcinoma) in the wild population. Such detailed disease analysis in wild animals is rarely possible. Once the prevalence of the disease was known throughout the population, a study protocol was implemented in 2009. During annual health checks randomly selected wild island foxes were treated with a topical medication to kill ear mites. Six months later treated and untreated individuals were reevaluated. ID microchips used on Channel Island foxes enabled biologists to accurately follow individual animals.

photo courtesy of M. Baffa

As the treatment study recounts, ear mite infection declined dramatically in treated wild island foxes. Continued annual treatment resulted in a reduction in ear canal irritation and decline in cancerous tumors. Not only did infected individual island foxes benefit, but transmission of ear mites to the next generation was dramatically reduced. Before the treatment study, nearly 90% of Catalina Island fox pups handled by biologists were found to carry ear mites transferred to them from their parents. 2015 health checks documented only 15% of the year's pups carried ear mites.

Breaking the cycle of ear mite infestation, irritation, cancer, and transmission to other foxes is good news for Catalina Island foxes.  It is also an example of the interconnection between various island fox conservation efforts. Annual monitoring and health checks, ID microchips, various conservation entities working together, these are all pieces of successful island fox recovery.

Why this subspecies of island fox is prone to cancerous ear tumors when foxes on other islands are not, remains unknown. Further research and genetic studies may offer new insight.

Read the Full Papers:
Prevalence of the disease: 
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0143211

Controlling the disease risk factors:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144271