Scientists: Fungus causes snake ailment, but reason elusive
MONTPELIER >> A fungus has been identified as the cause of a mysterious ailment that has been infecting some snake species in the eastern United States, threatening some isolated snake populations such as the timber rattlesnakes found in western Vermont.
Knowing for sure the cause of what has become known as snake fungal disease will make it possible for scientists to begin searching for the reason it has emerged and what, if anything, can be done to stop its spread or to protect snakes from it, said Jeffrey Lorch, a microbiologist with the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin.
Scientists still don't know for sure if the fungus, ophidiomyces ophiodiicola, was recently introduced to North America or if it has been here all along and something is now making it emerge and infect a number of snake species in at a number of states in the East and Midwest.
In the laboratory tests that led scientists to link the fungus with the disease, infected snakes changed their behavior in ways that could have made them more susceptible to predators or the environment and scientists are trying to determine if climate change is playing a role.
"These cold-blooded animals are going to be much more sensitive to even minor changes in climate," said Lorch, the lead author on the study published Nov. 17 in the journal MBio that linked the fungus to the disease. "And that might be why they are the canary in the coal mine. If this is a disease that is climate-change related, there is some concern that it is the tip of the iceberg."
Biologists have compared the appearance of snake fungal disease in the last decade to the fungus that causes white nose syndrome in bats, which since 2006 has killed millions of the creatures and continues to spread across North America.
In some areas snake fungal disease has been quite lethal while in others most infected snakes recover. For example, while timber rattlesnakes in the northeast have been hit hard, timber rattlesnakes populations in the upper Midwest seem to be coping with the infection, Lorch said.
"It's potentially fairly complex, trying to find if there's that threshold level that these populations might reach where conditions are just suddenly right for what might normally be an annoyance or just a mild infection to become deadly," Lorch said.
Although snake fungal disease affects a number of species, it's especially threatening to snake species such as slow-reproducing timber rattlesnakes that live in small, isolated populations with little genetic diversity, such as those found in Vermont, New Hampshire, Massachusetts and New York.
Among other states where the fungus has been found are Illinois, Florida, Minnesota, New Jersey, New York, Ohio, Tennessee and Wisconsin.
Doug Blodgett, the snake specialist for the Vermont Department of Fish and Wildlife, says they've confirmed the fungal disease in the state's rattlesnake population as well as the eastern rat snake and they suspect it in the milk snake. The biggest concern is for the state's timber rattlesnakes, estimated at several hundred in two locations not far from southern Lake Champlain.
"None of it's good. It's not a good thing," Blodgett said. "The reason this has bigger implications for the rattlesnake is because we have so few rattlesnakes left compared to these other species."
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