Over the past decade, biologists in the United States have been tracking the rise of a deadly disease affecting snakes. Exactly where it came from, how it spreads and what it means for infected snake populations are all still rather mysterious. Now, a new report has revealed the disease is popping up in far more places – and in more snake species – than we thought.

Snake Fungal Disease (SFD) is a skin condition that first caught scientists' attention back in 2006, when it struck a population of timber rattlesnakes in New Hampshire, cutting their numbers dramatically. Two years later, it wreaked similar havoc on rattlers in Illinois.

An eastern rat snake (Pantherophis alleghaniensis) showing signs of fungal infection, including opaque infected eye and roughened, crusty scales on the snout. Image: D.E. Green, USGS National Wildlife Health Center.

Since then, the number of reports has continued to rise. Just this past year has seen reports coming out of Virginia, Louisiana and Ontario – the first reported case outside the United States. The new report, put together by scientists from the US Geological Survey and colleagues, delivers the hard numbers: SFD has now been reported from at least 20 different states (plus Ontario), and it's affected more than 30 different snake species, from rattlers to rat snakes.

The disease has been on scientists' radar for only a short time, so they're still working on understanding it, but last year, the culprit was finally identified: a fungus named Ophidiomyces ophiodiicola. The disease causes blisters, ulcers, scabs and various other skin conditions in infected snakes. Most of the time, the effects seem to be fairly mild, but in some cases – for reasons that aren't fully understood – it can be extremely dangerous.

The New Hampshire outbreak detected in 2006 caused a 50% decline in the already-small population of local timber rattlesnakes. In Illinois, the fungus struck an endangered population of massasaugas (pygmy rattlers). A more recent case caused a decline of almost 20% in a community of Lake Erie watersnakes, a species that was only recently removed from the Threatened Species List.

"Some snake populations in the eastern and Midwestern US could eventually face extinction as a result of SFD," says Jeff Lorch, lead author of the new study. "[W]e still need to determine why these mild infections are becoming more severe and fatal in certain areas."

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A northern water snake (Nerodia sipedon) with crusty and thickened scales overlaying raised blisters as a result of a fungal skin infection, captured in western Lake Erie, Ohio. Image: D.E. Green, USGS National Wildlife Health Center.

It is possible the disease was introduced into the wild from captive snakes, but the new report highlights the possibility that the fungus has been out there for a while, and that changing conditions have given it the opportunity to go viral (or, in this case, fungal). The outbreak in New Hampshire, for example, happened during a time of particularly wet conditions. Increased temperatures might also be a factor, especially as the fungus targets snakes in their warm, cozy hibernation spots during the colder months.

"There is not a lot of information about Ophidiomyces ophidicola … in terms of virulence factors or how the fungus kills some snakes and not others," says Heather Fenton of the College of Veterinary Medicine at the University of Georgia, who wasn't part of this new study. The snakes hit hardest, she suggests, may have underlying conditions that make them more vulnerable. 

"It currently isn't clear that the fungus is necessarily spreading," Fenton says, though it is possible the disease is already present in more places than have been documented. Efforts are currently underway to assess just how widespread it might be, across the United States and elsewhere.

Worryingly, this is at least the third major fungal disease that has emerged recently as a threat to wildlife. Denizens of North America may be familiar with white-nose syndrome, a fungal condition that has been devastating bat populations by interrupting their hibernation cycle. And perhaps the most terrifying fungus of our time is the chytrid fungus that currently affects nearly 300 amphibian species in over 30 countries around the world.

Researchers point out that fungal diseases like SFD can be particularly dangerous because they can infect a variety of species and can survive in the environment outside of a host. Biologists are now worried that already-stressed populations of snakes – many currently threatened by other factors such as habitat loss or environmental changes – may fall victim to this opportunistic pathogen.

Snakes might not have a great reputation among many people, but they are crucial members of natural ecosystems, and as some of nature's most incredible predators, they control the spread of pests – like insects and rodents – that can damage crops and spread disease. We may not always get along with them, but a world without snakes would be neither a happy nor a healthy place.


Top header image: Frupus, Flickr