Epidemiology of sarcoptic mange in a geographically constrained insular red fox population

Abstract

Background: Sarcoptic mange is a skin disease caused by the contagious ectoparasite Sarcoptes scabiei, capable of suppressing and extirpating wild canid populations. Starting in 2015, we observed a multi-year epizootic of sarcoptic mange affecting a red fox (Vulpes vulpes) population on Fire Island, NY, USA. We explored the ecological factors that contributed to the spread of sarcoptic mange and characterized the epizootic in a landscape where red foxes are geographically constrained.

Methods: We tested for the presence of S. scabiei DNA in skin samples collected from deceased red foxes with lesions visibly consistent with sarcoptic mange disease. We deployed 96-100 remote trail camera stations each year to capture red fox occurrences and used generalized linear mixed-effects models to assess the affects of red fox ecology, human and other wildlife activity, and island geography on the frequency of detecting diseased red foxes. We rated the extent of visual lesions in diseased individuals and mapped the severity and variability of the sarcoptic mange disease.

Results: Skin samples that we analyzed demonstrated 99.8% similarity to S. scabiei sequences in GenBank. Our top-ranked model (weight = 0.94) showed that diseased red foxes were detected more frequently close to roadways, close to territories of other diseased red foxes, away from human shelters, and in areas with more mammal activity. There was no evidence that detection rates in humans and their dogs or distance to the nearest red fox den explained the detection rates of diseased red foxes. Although detected infrequently, we observed the most severe signs of sarcoptic mange at the periphery of residential villages. The spread of visual signs of the disease was approximately 7.3 ha/week in 2015 and 12.1 ha/week in 2017.

Conclusions: We quantified two separate outbreaks of sarcoptic mange disease that occurred > 40 km apart and were separated by a year. Sarcoptic mange revealed an unfettered spread across the red fox population. The transmission of S. scabiei mites in this system was likely driven by red fox behaviors and contact between individuals, in line with previous studies. Sarcoptic mange is likely an important contributor to red fox population dynamics within barrier island systems.

Keywords: Sarcoptes scabiei; Vulpes vulpes; Barrier island; Camera trapping; Ectoparasites; Epizootic outbreak; Red fox; Remote detection; Sarcoptic mange; Wildlife disease.

Fig. 1

Study areas on Fire Island, NY. Research efforts were focused in three areas (from east to west): (1) east of Old Inlet breach (gray), (2) central Fire Island (hashed), and (3) west Fire Island (black)

Fig. 2

Timeline of red fox (Vulpes vulpes) monitoring activity and observations of apparently healthy (orange) and diseased (turquoise) red foxes during each month of the study period across the three study areas at Fire Island (top to bottom corresponds to the east to west longitudinal gradient). Camera trapping periods are identified with bold boxes and indicate start (S) and end (E) months. 1 = diseased red fox first observed at the site, 2 = first known death of a diseased red fox, 3 = extirpation of red foxes, 4 = return of red foxes. Hashing illustrates months where both apparently healthy and diseased red foxes were seen, and periods when red foxes were extirpated and later returned

Fig. 3

Results of the top-ranked (global) generalized linear mixed-effects model. a Beta estimates and 95% confidence intervals (CIs) for covariates included in the top-ranked model. Predicted probability of detecting apparently healthy (orange) and diseased (turquoise) red foxes (Vulpes vulpes) in relation to b distance to human structures, c distance to a paved road, d distance to a diseased GPS-collared red fox territory, and e detection rates of other mammals. All covariates were standardized by two standard deviations. The solid line illustrates the mean estimate and ribbons depict 95% CIs

Fig. 4

Detection rates (detections per 100 trap nights) of apparently healthy (orange) and diseased (turquoise) red foxes (Vulpes vulpes) on Fire Island, NY during the boreal autumn and winters of (a) 2015/2016 east of the Old Inlet breach, (b) 2017/2018 at central Fire Island, and (c) 2017/2018 at the westernmost study area. Dates are listed as day-month

Fig. 5

Visual severity of sarcoptic mange in red fox (Vulpes vulpes) during the boreal autumn and winters of (a) 2015/2016 in the study area east of the Old Inlet breach, (b) 2017/2018 at central Fire Island immediately west of the Old Inlet breach, and (c) 2017/2018 at the westernmost study area. Black points illustrate locations of fox dens from the previous summer and colored points illustrate locations of camera stations. The size of camera location points reflects the severity (maximum) and color reflects variability (interquartile range)