Impact of Snake Fungal Disease on Population Viability

Snake fungal disease (SFD) is an emerging fungal pathogen infecting both wild and captive snake species. The causative agent of SFD is Ophidiomyces ophiodiicola, a keratinophilic soil inhabiting fungus. Clinical signs of SFD include swelling, abnormal scales, and skin lesions. The last extant population of Eastern Massasauga Rattlesnakes (Sistrurus catenatus) in Illinois has an annual SFD prevalence rate of 15-22%, and evidence suggests mortality rates may be as high as 90%. Eastern Massasaugas were listed as federally threatened under the Endangered Species Act in 2016, and thus the impact of disease on the viability of wild populations is of great conservation concern. We used data from 15 years of demographic population monitoring and five years of SFD surveillance to conduct a population viability analysis (PVA). We used the Meta-Model Manager extension of Vortex PVA software to merge our demographic PVA model with the SFD disease dynamics model developed in the Vortex Outbreak extension. Our results show that SFD increases the probability of extinction of the Illinois population, and thus is likely a threat to the persistence of the species range-wide.