A fungal disease that is killing snakes in parts of the United States is present in more states than previously documented, according to a U.S. Geological Survey report published today.
USGS scientists and partners detected Ophidiomyces ophiodiicola, the fungus that causes snake fungal disease (SFD), in at least 20 states in the eastern U.S., and in numerous snake species not formerly known to harbor the fungus. These findings increase the total number of confirmed susceptible snake species to 30. Snakes affected by SFD include the threatened eastern massasauga rattlesnake.
The report also shows that SFD infections are often mild, but there are unknown factors that cause outbreaks of severe skin disease and death.
“Some snake populations in the eastern and midwestern U.S. could eventually face extinction as a result of SFD,” said Jeff Lorch, a USGS scientist and the lead author of the report. “Our new findings increase our understanding of the geographic extent, species susceptibility and manner of development of this disease. These results will offer important clues regarding how to manage SFD.”
Snakes are valuable because they prey upon pests that damage agricultural crops and rodents that can carry disease, and they serve as food for many other animals. SFD, which first gained attention in the U.S. in 2006, produces thickened skin, ulcers, blisters and emaciation in infected snakes.
From 2009-2015, the scientists examined samples from 82 wild snakes submitted to the USGS National Wildlife Health Center from partners in the eastern U.S. Of the snakes that had skin abnormalities, 76 percent were positive for O. ophiodiicola. These findings suggest that O. ophiodiicola is the predominant fungus associated with skin infections in wild snakes.
The USGS scientists, in collaboration with the Wisconsin and Minnesota Departments of Natural Resources, also captured 206 snakes from Minnesota and Wisconsin during late April to late May in 2013-2015, after the snakes emerged from hibernation. Forty-one percent of the captured snakes had skin lesions similar to those associated with SFD, and almost all of the lesions were relatively mild. Over half of the samples tested from these snakes were positive for the O. ophiodiicola fungus.
“Our findings suggest that O. ophiodiicola most often causes mild, non-lethal skin lesions in snakes, which gives us hope that snakes may be able to clear some infections,” Lorch said. “However, we still need to determine why these mild infections are becoming more severe and fatal in certain areas.”
O. ophiodiicola is not known to affect humans or other animals.
The study is published in the journal Philosophical Transactions of the Royal Society B.
For more information about USGS wildlife disease research, please visit the USGS National Wildlife Health Center website. More information about SFD is also available on the USGS Wetland and Aquatic Research Center website.