Prevalence Rates of Snake Fungal Disease and its Population-Level Impacts in a Snake Assemblage in Southwest Louisiana

Science Center Objects

In the last twenty years, an extraordinary number of fungal and fungal-like diseases have caused some of the most severe die-offs and extinctions ever observed in wild species.

Examples of Snake Fungal Disease (SFD)
Examples of Snake Fungal Disease (SFD); Photo: USGS

The Science Issue and Relevance: In the last twenty years, an extraordinary number of fungal and fungal-like diseases have caused some of the most severe die-offs and extinctions ever observed in wild species. Snake Fungal Disease (SFD) is a recently documented mycotic disease and an emerging threat to wild snake populations, and is deemed a global conservation issue. SFD became more widely known after two 2011 publications documented high mortality rates caused by SFD in two protected species of pit viper in the Midwestern and northeastern United States. Snake Fungal Disease was confirmed in Louisiana in 2015, but virtually nothing is known about prevalence rates or populations impacted by SFD in the southeastern United States.

Methodology for Addressing the Issue: We use visual encounter surveys to sample snakes in a capture-mark-recapture (CMR) approach in a small area (~ 3 ha) of semi-permanent and ephemeral wetlands at Palmetto Island State Park (PISP). This site was chosen due to the presence of snakes with clinical signs of SFD and the belief that snakes, notoriously hard to recapture, may be recaptured here with some success. After sexing and taking standard measurements of captured snakes, each snake is marked by injection of a PIT (Passive Integrated Transponder) tag and then branded using a medical cauterizer. After diagramming all areas of possible dermatitis, we take 1-4 swabs of each snake dependent upon the severity of clinical signs of SFD. All areas swabbed are also photographed. We will use a real-time polymerase chain reaction (qPCR) assay to detect O. ophiodiicola, the causative agent of SFD, on our swab samples. Marking, swabbing, and photographing each capture allows us to determine prevalence rates by species, and investigate disease progression and its possible effects on fitness and survival.

Future Steps: We will continue CMR at PISP to refine prevalence rates of snake fungal disease. In the short-term, by examining swab results, we will gain a better understanding of the types of dermatitis that are likely to produce positive results, which will inform our field methodology. In the long-term, with more data and recaptures, we will gain an understanding of how the disease is affecting individual snakes over time and the overall snake population at this site. Because our climate is much milder than areas where SFD is currently being studied, it is likely that the disease will manifest differently here than in areas where the snakes undergo an extended dormancy period.

Additional publication resulting from this research:

Lorch JM, Lankton JS, Knowles S, Michell K, Edwards JL, Kapfer JM, Staffen RA, Wild ER, Schmidt KZ, Ballman AE, Blodgett D, Farrell TM, Glorioso BM, Last LA, Price SJ, Schuler KL, Smith CE, Wellehan JFX, Jr., Blehert DS. Snake fungal disease: an emerging threat to wild snakes. Proceedings of the Royal Society of London. Series B-Biological Sciences, In press.

Related Project(s): None