Sarcoptic mange poses a serious conservation threat to endangered San Joaquin kit foxes (Vulpes macrotis mutica). After first appearing in Bakersfield, California in spring 2013, mange reduced the kit fox population approximately 50% until the epidemic ended with minimally detectable endemic cases after 2020. Mange is lethal and thus, with such a high force of infection and lack of immunity, it remains unclear why the epidemic did not burn itself out rapidly and how it persisted so long. Here we explored spatio-temporal patterns of the epidemic, analyzed historical movement data, and created a compartment metapopulation model (named "metaseir") to evaluate whether movement of foxes among patches and spatial heterogeneity would reproduce the eight years epidemic with 50% population reduction observed in Bakersfield. Our main findings from metaseir were that: 1) a simple metapopulation model can capture the Bakersfield-like disease epidemic dynamics even when there is no environmental reservoir or external spillover host, 2) the most impactful parameter on persistence and magnitude of the epidemic is the projection, β/αβ (transmission over decay rate of transmission over space), 3) heterogeneity in patch carrying capacities changes the critical value of the projection needed to achieve an epidemic but makes little difference to epidemic persistence time, and 4) the epidemic is relatively insensitive to birth rates and density vs. frequency-dependent transmission. Our model can help guide management and assessment of metapopulation viability of this vulpid subspecies, while the exploratory data analysis and model will also be valuable to understand mange in other, particularly den-occupying, species.

A robust population of endangered San Joaquin kit foxes occurs in the city of Bakersfield, CA. In March 2013, sarcoptic mange was detected in this population and the disease quickly spread. In January 2019, mange also appeared in a smaller kit fox population in the neighboring town of Taft, CA. To date there have been more than 430 confirmed cases in and 100 confirmed deaths of kit foxes. An additional 118 unrecovered individuals are presumed deceased because there is no indication that kit foxes survive without medical intervention. These numbers are also presumed underestimations of the actual number of kit foxes that have contracted and died from mange. In addition to capturing and treating kit foxes, the Endangered Species Recovery Program has conducted a yearly citywide camera survey in Bakersfield since 2015 and Taft since 2019 to assess the occurrence of mange among kit foxes and the spatial pattern of spread. Based on the Bakersfield survey, the urban kit fox population has declined by 67% since 2015. This annual camera survey also provides information on co-occurring species that could contract or transmit mange. Of the total number of cameras that have detected kit foxes with mange, 88% of those also detected at least one secondary species including raccoons, opossums, striped skunks, California ground squirrels, and domestic cats and dogs. The annual camera surveys have also detected coyotes, red foxes, gray foxes, and opossums with active mange infestations. Transmission routes for all of these species remain uncertain and the potential for transmitting mites to new areas or new individuals of multiple species is possible. Overall, mange presents a risk to multiple species in the urban environment, including domestics, for as long as it continues to circulate.