What can museum specimens tell us about the history of Snake Fungal Disease?


Dead on the road Timber and Eastern Dimond-backed Rattlesnakes preserved in the Georgia Southern University Herpetology Collection – Houston Chandler

Some of the first questions that emerge when a new wildlife disease is documented surround where the disease originated and how long has it been impacting wildlife populations. Is the disease emerging or has it been around for decades? Perhaps something else in the environment is just now making the disease bad enough that it is noticeable to biologists. These types of questions are often exceedingly difficult to answer because historical data is often lacking for obvious reasons. Sometimes genetic data can be used to illuminate the origins of diseases, as has been recently done for the Chytrid fungus found in amphibian populations (O’Hanlon et al. 2018).

Snake Fungal Disease (SFD, also known as ophidiomycosis) is one of the so-called emerging diseases that can affect herpetofauna. Caused by the fungal pathogen Ophidiomyces ophiodiicola, SFD has now been documented in a plethora of snake species across the eastern United States as well as in snakes from Europe. SFD was suggested as a contributing factor to declines in a Timber Rattlesnake population (Clarke et al. 2011) and was noted to be impacted Eastern Massasaugas (Allender et a. 2011). Furthermore, recent studies have documented how snakes infected with ophidiomycosis behave differently than uninfected individuals (Tetzlaff et al. 2017), suggesting there are costs other than death that can arise from an SFD infection. From the first documented cases to description of the pathogen and its effects has occurred over approximately 10 years but offers little insight into whether SFD has been impacting snakes for longer without documentation.

New research by Lorch et al. (2021) aims to shed more light on this history of SFD in America’s snake populations. The authors examined 524 snake specimens, representing 30 species, that were preserved in natural history collections. All specimens were visually inspected for clinical signs of SFD (i.e., skin lesions), and 47 individuals (12 species from 7 states) had clinical signs that were consistent with an SFD infection. However, a confirmed ophidiomycosis infection requires the confirmation of both histopathologic lesions and O. ophiodiicola DNA from the infected area. Thus, Lorch et al. (2021) also examined a subset of specimens (n = 12) to look for these additional indicators of an infection. Of these 12 snakes, 7 had microscopic lesions that were characteristic of ophidiomycosis. Furthermore, the author’s found that 3 of the 6 specimens stored in ethanol (the other 6 were stored in formalin, which degrades DNA) tested positive for O. ophiodiicola DNA. This DNA was identical to sequences found in contemporary studies. Importantly, the snakes that were positive for fungal DNA were collected in Florida in 1945, Wisconsin in 1958, and Tennessee in 1973. That pushes the first documented SFD case back over 50 years! These samples were from a Timber Rattlesnake, a Scarlet Snake, and a Rat Snake, all species that have been documented with ophidiomycosis in recent years.

Scarlet Snake from southern Georgia being sampled for O. ophiodiicola DNA – Houston Chandler

These results indicate that O. ophiodiicola has been present in snake populations for decades in the eastern United States before it was even identified as an emerging fungal pathogen. The specimens observed in this study also came from a large geographic area, which also suggests that the widespread prevalence of ophidiomycosis is not a recent development. These results are not particularly surprising but highlight how pathogens can go undocumented for long periods of time. It remains unclear why it took so long to diagnose ophidiomycosis as a potential conservation threat for snake populations, and as Lorch et al. (2021) point out, more work is needed to better understand how environmental changes are impacting disease dynamics. Have environmental conditions changed, making snake population more susceptible to disease in the 21st century?

Finally, this study highlights one of the many benefits that natural history collections can provide. Without this historic record of specimens, it would not have been possible to examine snakes from over 50 years ago for a disease only identified during the 2010s.


Literature Cited

Allender, M. C., M. Dreslik, S. Wylie, C. Phillips, D. B. Wylie, C. Maddox, M. A. Delaney, and M. J. Kinsell. 2011. Chrysosporium sp. infection in Eastern Massasauga Rattlesnakes. Emerging Infectious Diseases 17:2383–2384.

Clark, R. W., M. N. Marchand, B. J. Clifford, R. Stechert, and S. Stephens. 2011. Decline of an isolated timber rattlesnake (Crotalus horridus) population: Interactions between climate change, disease, and loss of genetic diversity. Biological Conservation 144:886–891.

Lorch, J. M., S. J. Price, J. S. Lankton, and A. N. Drayer. 2021. Confirmed cases of ophidiomycosis in museum specimens from as early as 1945, United States. Emerging Infectious Diseases 27:1986–1989.

O’Hanlon, S. J., A. Rieux, R. A. Farrer, G. M. Rosa, B. Waldman, A. Bataille, T. A. Kosch, K. A. Murray, B. Brankovics, M. Fumagalli, M. D. Martin, N. Wales, M. Alvarado-Rybak, K. A. Bates, L. Berger, S. Böll, L. Brookes, F. Clare, E. A. Courtois, A. A. Cunningham, T. M. Doherty-Bone, P. Ghosh, D. J. Gower, W. E. Hintz, J. Höglund, T. S. Jenkinson, C.-F. Lin, A. Laurila, A. Loyau, A. Martel, S. Meurling, C. Miaud, P. Minting, F. Pasmans, D. S. Schmeller, B. R. Schmidt, J. M. G. Shelton, L. F. Skerratt, F. Smith, C. Soto-Azat, M. Spagnoletti, G. Tessa, L. F. Toledo, A. Valenzuela-Sánchez, R. Verster, J. Vörös, R. J. Webb, C. Wierzbicki, E. Wombwell, K. R. Zamudio, D. M. Aanensen, T. Y. James, M. T. P. Gilbert, C. Weldon, J. Bosch, F. Balloux, T. W. J. Garner, and M. C. Fisher. 2018. Recent Asian origin of chytrid fungi causing global amphibian declines. Science 360:621–627.

Tetzlaff, S. J., M. J. Ravesi, B. A. Degregorio, M. C. Allender, J. M. Josimovich, E. T. Carter, and B. A. Kingsbury. 2017. Snake fungal disease affects behavior of free-ranging Massasauga Rattlesnakes (Sistrurus catenatus). Herpetological Conservation and Biology 12:624–634.