Ultraviolet Fluorescence as a Non-Invasive Diagnostic Tool for Ophidiomycosis in Lake Erie Watersnakes (Nerodia sipedon insularum)
Diagnosis of ophidiomycosis (Ophidiomyces ophiodiicola) currently requires one or a combination of (1) a positive quantitative PCR (qPCR) result from a skin swab, (2) a positive fungal culture, or (3) characteristic histopathology lesions from a skin biopsy. While reliable, these methods can have a long turnaround time. Long-wave ultraviolet (UV) light has been used to diagnose fungal infections, most recently white-nose syndrome in bats. If applicable to ophidiomycosis, UV light could provide a reliable field-applicable diagnostic tool. Fluorescence intensity from UV light (Phillips Burton Model UV502, 120V) was compared to qPCR analysis to detect O. ophiodiicola infections in 38 Lake Erie watersnakes (Nerodia sipedon insularum). Photos of snake skin were taken under UV exposure and analyzed to obtain a fluorescence intensity (FI) measurement (ImageJ, v1.52a, National Institutes of Health, USA). An FI value of 105u determines whether a lesion visually fluoresces with 74% accuracy (specificity=95%, sensitivity=68%). Areas of skin that were exposed to UV light were swabbed and analyzed by qPCR to determine fungal quantity. FI of skin lesions under UV light was compared to qPCR results: FI values from 105–147.7u were likely to be qPCR positive for O. ophiodiicola, with an accuracy of 77% (sensitivity=80%, specificity=77%). This evidence supports the use of visual fluorescence identification as a limited method to diagnose ophidiomycosis in Lake Erie watersnakes. Ultimately, qPCR of a skin swab should be performed in conjunction with fluorescence for a definitive diagnosis, but UV light can provide a preliminary, non-invasive, and field-applicable method to detect the presence of O. ophiodiicola.