A new disease of snakes has been quietly spreading across the U.S. The disease known as Snake Fungal Disease (SFD) is believed to be caused by a fungus called Ophidiomyces ophiodiicola and so far has been found in 15 states in the eastern half of the U.S. The disease has been discovered as far west as Minnesota, but biologists suspect that SFD is more widespread in the U.S. than is currently documented.  

A strange skin disease affecting snakes have been known to wildlife biologists since the mid-2000s, but “over the past few years, the number of snakes with the disease appears to be increasing,” says Jeffrey Lorch, a microbiologist at the USGS National Wildlife Health Center in Madison, Wisconsin, who recently developed a rapid molecular test for the fungus. The disease affects different species of snakes differently; however, snakes with SFD commonly have crusty-looking scales, scabs, nodules under the skin, or experience premature molting. Some may also have nodules in deeper tissues and swelling of the face.   

D.E. Green/USGS
D.E. Green/USGS

SFD affects multiple species of snakes – including venomous copperheads, cottonmouths, and rattlesnakes, in addition to some nonvenomous varieties such as milk snakes, corn snakes and garter snakes. The disease has come to the attention of wildlife conservationists because it affects timber rattlesnakes and the Eastern Massasauga, snakes that are listed as either threatened or endangered in several states.  The disease was first documented in 2006 in New Hampshire, where there was a 50% decline in a population of timber rattlesnakes due to the disease.          

Some biologists see parallels between SFD and another emerging fungal disease, called White Nose Syndrome – threatening bat populations throughout the eastern and midwestern U.S. While there are similarities, however, it should be pointed out that the two diseases are caused by different species of fungi and have different ecological niches in nature.

“Currently, we do not know the origins of this fungus,” said Lorch.  “Many people think that [it] must have been introduced [into the U.S.]; however, we do not really have any evidence of that.”  “This could just be a pathogen that has been overlooked until other factors – like climate change – exacerbated the disease and made it more visible,” said Lorch.

According to a study recently published in the journal Fungal Ecology, the SFD fungus likes to eat keratin, the stuff that makes up snake scales – and a key component of human skin, fingernails, and hair.  While this type of fungus rarely causes disease in healthy mammals, the risk to human health from the fungus is currently unknown.     


Chris A. Whitehouse is a microbiologist and science writer who lives in Maryland.  He writes extensively on emerging infectious diseases of humans and wildlife.  

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