Comparison of Testing Methods for Snake Fungal Disease

Snake fungal disease (SFD) is an emerging fungal pathogen infecting both wild and captive snake species. The causative agent of SFD has been identified as Ophidiomyces ophiodiicola, a keratinophilic soil inhabiting fungus. Clinical signs of SFD include abnormal scales and skin lesions, but testing is required for confirmation. Diagnosis requires either identifying the fungus directly in tissues or demonstrating evidence of pathogen with clinical signs. Historically, this is performed using skin biopsies or swabs and qPCR for O. ophiodiicolaDNA detection. We tested the agreement of qPCR of biopsies and swabs in free-ranging Eastern Massasauga Rattlesnakes (Sistrurus catenatus) in Illinois from 2014-2016. All snakes were captured each year during the spring egress period as part of a long-term monitoring project. All individuals exhibiting clinical signs of SFD were swabbed and a punch biopsy was taken from affected areas. DNA was extracted similarly from each sample and concentration of DNA was determined using spectrophotometry. Quantitative PCR was then used to test for the presence of O. ophiodiicola. Fungal copy numbers amplified were standardized per ng of total DNA in the sample. Our data shows near total agreement (mean difference: 4.86 fungal copies higher in swabs) between the two methods. As such we suggest SFD testing be done using swabs/qPCR as it is less invasive for the animal, but further evaluation is still needed to determine the sensitivity and specificity of all available assays.