Background: In 2013, sarcoptic mange, caused by Sarcoptes scabiei mites, precipitated a catastrophic decline of the formerly stable urban population of endangered San Joaquin kit foxes ( Vulpes macrotis mutica ) in Bakersfield, California, USA. In 2019, a smaller sarcoptic mange outbreak affected kit foxes 58 km southwest of Bakersfield in the town of Taft, California. To determine whether the Taft outbreak could have occurred as spillover from the Bakersfield outbreak and whether epidemic control efforts must involve not only kit foxes but also sympatric dogs ( Canis lupus familiaris ), coyotes ( Canis latrans ), and red foxes ( Vulpes vulpes ), we evaluated genotypes and gene flow among mites collected from each host species.
Methods: We used 10 Sarcoptes microsatellite markers (SARM) to perform molecular typing of 445 S. scabiei mites collected from skin scrapings from twenty-two infested kit foxes, two dogs, five coyotes, and five red foxes from Bakersfield, Taft, and other nearby cities.
Results: We identified 60 alleles across all SARM loci; kit fox- and red fox-derived mites were relatively monomorphic, while genetic variability was greatest in Bakersfield coyote- and dog-derived mites. AMOVA analysis documented distinct mite populations unique to hosts, with an overall F ST of 0.467. The lowest F ST (i.e. closest genetic relationship, F ST = 0.038) was between Bakersfield and Taft kit fox-derived mites while the largest genetic difference was between Ventura coyote- and Taft kit fox-derived mites (F ST = 0.843).
Conclusion: These results confirm the close relationship between the Taft and Bakersfield outbreaks. The Sarcoptes host specificity suggests that, although an inter-species spillover event likely initiated the kit fox mange outbreak, mite transmission is now primarily intraspecific. Therefore, any large-scale population level intervention should focus on treating kit foxes within the city.