Houston ChandlerViews:
Over the last two years, we have sampled the snake fauna of southeastern Georgia for Ophidiomyces ophiodiicola, the causative agent of Snake Fungal Disease (SFD). SFD has now been identified in snakes across the eastern United States, including several severe cases in Georgia that prompted this study. We sampled snakes through a variety of methods (road cruising, visual encounter surveys, and drift fencing) and collected swab samples from all encountered snakes. Samples were collected from around the face (an area that often displays the worst SFD symptoms) of all individuals and additional samples were collected from other areas of the snake’s body that had skin lesions or areas that may indicate a disease infection. All samples were tested for Ophidiomyces DNA using a qPCR approach and a combination of these test results and the presence of skin lesions were used to assess the results of these surveys.
We collected 962 samples from 786 snake encounters and 34 snake species. Samples were collected from a variety of both public and private properties across 39 Georgia counties. Of the 786 snakes sampled, 276 (35.1%) had lesions on the skin that could indicate ophidiomycosis, and 137 (17.4%) snakes tested positive for Ophidiomyces ophiodiicola DNA. Positive individuals had skin lesions a majority of the time (85%), but a small number of individuals did test positive for Ophidiomyces ophiodiicola without any sign of infection or disease. Snakes testing positive for Ophidiomyces ophiodiicola DNA represented 22 species, with infection rates varying significantly among species. Eastern Indio Snakes (Drymarchon couperi), Brown Watersnakes (Nerodia taxispilota), and Plain-bellied Watersnakes (Nerodia erythrogaster) tested positive at the highest rates. At least one individual of all five species of native pit viper tested positive, although Cottonmouths (Agkistrodon piscivorus) were the only pit viper with an infection rate above 25%. Geographically, Ophidiomyces ophiodiicola DNA was detected in snakes from 25 counties across southeastern Georgia. All but one county with greater than 10 samples collected had at least one positive snake.
Eastern Indigo Snakes commonly had blisters, scabs or discolored scales along their bodies and near the vent. Approximately 44% of Eastern Indigo Snakes captured over the two-year period tested positive for Ophidiomyces ophiodiicola DNA. Positive tests were common from swabs taken directly from dorsal lesions or scabs near the vent. Despite the high prevalence of Ophidiomyces ophiodiicola observed in Georgia populations of Eastern Indigo Snakes, most individuals had good body condition. Less than five individuals had a severe infection that was negatively impacting their overall health (one individual was treated and recovered at the Georgia Sea Turtle Center). We captured 14 individuals multiple times during the course of the study. Only one of these snakes tested positive and then negative at a later date, although five individuals tested negative on multiple occasions.
Overall, our results indicate that the fungal pathogen responsible for SFD is widespread in Georgia, both geographically and taxonomically. However, there remain many unanswered questions surrounding this disease and its impacts on native snake populations. First, it is still unclear how many snakes that are infected with SFD actually succumb to their infections or are impacted in a way that negatively effects some part of their life history (e.g., reproductive success). Snakes are notoriously difficult to study and recapture rates in marked populations are generally low. More work is needed to better understand what happens to individuals after they become infected. Second, we know relatively little about the impacts of SFD at the population level. Some studies have seemingly linked disease to population declines in snakes, but more research is needed to understand how disease infection impacts populations at a broad scale. Third, given the wide distribution of positive snakes in this and other studies, it is not clear how snakes are becoming infected with Ophidiomyces ophiodiicola. The mechanisms that lead to infection, particularly severe infections, are an important aspect of understanding SFD’s effects on native snakes. Ultimately, there is a significant amount of research that still needs to occur before we begin to fully understand this disease and its impacts on snake populations.
