Spatio-temporal and transmission dynamics of sarcoptic mange in an endangered New World kit fox

Den Use Patterns of Endangered San Joaquin Kit Foxes in Urban Environments May Facilitate Disease Transmission

A robust population of endangered San Joaquin kit foxes (Vulpes macrotis mutica; SJKFs) occurs in the city of Bakersfield, CA. In 2013, sarcoptic mange was detected and significantly reduced SJKF abundance. Dens may be a mode of mange mite transmission. Kit foxes use dens daily and sometimes share dens. Also, mange mites are able to live off-host in den soil for multiple days. We monitored den use patterns of 37 marked kit foxes. Radio-collared foxes were tracked to dens and then those dens were monitored with cameras for 7-day sessions, the period of time mites might persist in the dens. Other foxes used the same den as a collared fox during 89.0% of sessions and the mean number was 2.5 foxes. An average of 1.8 foxes used a den concurrently with the collared fox. During 120-day intervals, the minimum survival time for kit foxes contracting mange, collared foxes used a mean of 7.6 dens, 9.8 other foxes used the same dens, and 7.3 foxes used the dens concurrently with the collared foxes. Thus, the potential for kit foxes to transmit mange through den sharing in the urban environment is considerable and may explain the rapid spread of mange throughout this population.

Estimating the impact of sarcoptic mange epidemic on the population size of wild raccoon dogs (Nyctereutes procyonoides) from wildlife rescue data

The impact of infectious diseases on host populations is often not quantified because it is difficult to observe the host population and infectious disease dynamics. To address this problem, we developed a state-space model to simultaneously estimate host population and disease dynamics using wildlife rescue data. Using this model, we aimed to quantify the impact of sarcoptic mange on a Japanese raccoon dog population by estimating the change in their relative population size. We classified the status of rescued raccoon dogs into four categories: i) rescued due to infection with mange, ii) rescued due to traffic accidents without mange, iii) rescued due to traffic accidents with mange, and iv) rescued due to causes other than traffic accidents or mange. We modelled the observation process for each category and fitted the model to the reported number of raccoon dogs rescued between 1990 and 2010 at three wildlife rescue facilities in Kanagawa Prefecture, Japan. The mortality rate induced by mange was estimated to be 1.09 (95% credible interval (CI): 0.47-1.72) per year. The estimated prevalence of sarcoptic mange ranged between 4 and 80% in the study period. When a substantial prevalence of mange was observed (1995-2002), the host population size decreased by 91.2% (95% credible intervals: 86.3-94.7). We show that the impact of infectious disease outbreak on the wildlife population can be estimated from the time-series data of wildlife rescue events due to multiple causes. Our estimates suggest that sarcoptic mange triggered a substantial decrease in the Japanese wild raccoon dog populations.

A compartment and metapopulation model of Rocky Mountain spotted fever in southwestern United States and northern Mexico

Rocky Mountain spotted fever (RMSF) is a fatal tick-borne zoonotic disease that has emerged as an epidemic in western North America since the turn of the 21st century. Along the US south-western border and across northern Mexico, the brown dog tick, Rhipicephalus sanguineus, is responsible for spreading the disease between dogs and humans. The widespread nature of the disease and the ongoing epidemics contrast with historically sporadic patterns of the disease. Because dogs are amplifying hosts for the Rickettsia rickettsii bacteria, transmission dynamics between dogs and ticks are critical for understanding the epidemic. In this paper, we developed a compartment metapopulation model and used it to explore the dynamics and drivers of RMSF in dogs and brown dog ticks in a theoretical region in western North America. We discovered that there is an extended lag-as much as two years-between introduction of the pathogen to a naïve population and epidemic-level transmission, suggesting that infected ticks could disseminate extensively before disease is detected. A single large city-size population of dogs was sufficient to maintain the disease over a decade and serve as a source for disease in surrounding smaller towns. This model is a novel tool that can be used to identify high risk areas and key intervention points for epidemic RMSF spread by brown dog ticks.