Tracking Outcomes of Snake Fungal Disease in Free-ranging Pygmy Rattlesnakes ( Sistrurus miliarius).

Snake fungal disease (SFD) is caused by the fungus Ophidiomyces ophiodiicola and its documentation in wild snake populations has risen sharply in the past decade. Little is known regarding the fate of individual, free-ranging snakes afflicted with SFD. We monitored an afflicted population of pygmy rattlesnakes ( Sistrurus miliarius) at Lake Woodruff National Wildlife Refuge in Central Florida, US for 2 yr. The severity of SFD in individual snakes was unrelated to the probability of their recapture later in the study, and half of the snakes diagnosed as severely infected at the onset of the study were recaptured later with no clinical signs of SFD. The clinical progress of 12 serially recaptured individuals also showed that individuals cleared the infection and fluctuated between no or low and severe clinical signs over the 2-yr study.

Environmental and physiological correlates of the severity of clinical signs of snake fungal disease in a population of pigmy rattlesnakes, Sistrurus miliarius.

In the past decade, snake fungal disease (SFD) has been identified as an emerging threat to snake populations throughout the eastern USA. Snake fungal disease is caused by the fungus Ophidiomyces ophiodiicola. Little is known regarding the environmental or physiological variables that affect host vulnerability and O. ophiodiicola virulence in wild snake populations. Understanding the intrinsic and extrinsic factors that correlate with infection severity is a key first step in understanding host-pathogen dynamics. Host vulnerability may vary seasonally as a result of thermal conditions or energetic trade-offs, and pathogen growth rates or dispersal may be tied to seasonal trends in climate. To determine whether season, environmental temperature or energetic trade-offs associated with life-history stage influence an individual's susceptibility to infection, we monitored the severity of clinical signs of SFD, surface air temperature, reproductive status, body condition and serum complement activity (plasma bactericidal ability) in free-ranging pigmy rattlesnakes, Sistrurus miliarius, over the course of 18 months. Seasonal increases in the severity of clinical signs of SFD were correlated negatively with monthly air surface temperature and the mean body condition of the population. Bactericidal ability varied seasonally, but pigmy rattlesnakes suffering from active SFD infections did not exhibit deficits in innate immune function. Infected snakes were in significantly lower body condition when compared with the general population, but seasonal patterns in the mean body condition of the population were not driven by seasonal patterns of infection severity. Our results highlight the potential importance of the thermal environment and energetic status in determining infection severity and outcomes and the need for managers and researchers to consider seasonality of symptom presentation when the goal is to identify the prevalence or incidence of SFD in populations.