Abstract

The island fox (Urocyon littoralis) is only found on six Channel Islands off the coast of Southern California and is the largest terrestrial carnivore on the islands. Since 1994, island fox populations have experienced severe declines (up to 95%), which have resulted in the recent listing of the four most affected subspecies as federally endangered on March 4, 2004. An outbreak of canine distemper virus in 1999 is believed to be responsible for the dramatic decline of the Santa Catalina Island fox population, but little is known about current pathogen exposure in the entire fox population at risk. Prior to the decline, fox populations on all six islands had no evidence of exposure to canine distemper virus (CDV), while exposure to other canine viral pathogens, Toxoplasma gondii and Leptospira interrogans serovars varied among islands. Our study investigates what role infectious diseases like distemper may have had in the declines by estimating the exposure prevalence of infectious diseases in the post-decline island fox population.

To date, 218 island fox serum samples collected from 2001 through 2003 on all six islands have been analyzed for exposure to canine distemper virus, canine adenovirus-1, canine parvovirus, canine coronavirus, canine herpes virus, and six Leptospira serovars at Cornell University Veterinary Diagnostic Laboratory. Our results indicate that canine parvovirus and adenovirus exposure is still prevalent on most islands, and that Santa Catalina Island remains naive to adenovirus exposure. In contrast to pre-decline serology, foxes on all six islands now have evidence of exposure to CDV (11.8% on San Miguel Island, 4.8% on Santa Rosa Island, 63.6% on Santa Cruz Island, 33.3% on Santa Catalina Island, 27.7% on San Clemente Island, and 68.9% on San Nicolas Island). On islands where some or all of the current population is being held in captivity, stratification of CDV antibody titers by fox birth location (captivity vs. wild-born) reveals that titers are only present in wild-born foxes. These results suggest that wild fox populations on all six islands have been exposed to CDV or a closely related morbillivirus in the past, but it is not known why Santa Catalina Island foxes appeared to have high mortality while the fox population on San Nicolas Island has remained stable despite having the highest CDV antibody prevalence. These initial antibody titer results have been used by managers making decisions regarding vaccination programs for wild and captive island foxes and will be used to help assess the risk of moving island foxes to and from the mainland or between islands for captive breeding.