Fungi are giving wildlife a real beating these days. Chytrid is walloping frog and salamander species worldwide, and here in the United States, white-nose syndrome, caused by an invasive European fungus, has killed millions of bats on the East Coast and is spreading west. Also worth mentioning is the nosema fungus, which may play in colony collapse disorder, a phenomenon devastating bees, and potentially the crops they pollinate, across the globe.
Now a fungal pathogen could be after our snakes, too. And it’s not pretty.
Snake fungal disease, or SFD, is a little-known illness leaving snakes with gruesome, often-fatal skin lesions. First documented in 2008 on a rat snake in Georgia, the fungus has since infected at least seven snake species in 11 states, and scientists think it could spread. Within affected regions—mostly in the Northeast and Midwest—researchers are quickly assessing their snake populations and looking for signs of illness. These range from small bumps to severe blisters on the skin, cloudy eyes, lesions along the snake’s body, and facial deformities around the eyes and nose. (Illinois’ massasauga rattlesnakes seem especially vulnerable to the disease, suffering from grotesque facial disfigurement and near-certain death.)
“It’s got everyone worked up and worried about what the heck is going on,” says Doug Blodgett, a wildlife biologist for Vermont Fish and Wildlife Department. So far biologists there have discovered the fungus only on the state’s endangered timber rattlesnakes, but they think more species are at risk.
Without the timber rattler, the Northeast would lose its only rattlesnake, an important player in the region’s forests (see “Tick, Rattle, and Roll”). The snake’s numbers plummeted in the 20th century thanks to bounty programs that put a price on its skin. Making matters worse, development has isolated populations of the species from each other, and low genetic diversity within those groups has put the species as a whole in a precarious position. “We are already in trouble,” says Blodgett, “and I’m concerned this might be a tipping point.”
The main suspect behind the serpent sickness is the fungus Ophidiomyces ophiodiicola, but scientists have yet to positively identify the killer. O. ophiodiicola has been found on infected animals, but researchers need to prove that it’s the true culprit, because wild snakes are typically covered with many different types of fungi. So Jeff Lorch, a researcher at the University of Wisconsin-Madison, and his colleagues at the National Wildlife Health Center in Madison are testing both healthy and sick snakes from different parts of the country to see if O. ophiodiicola consistently comes along with the disease’s characteristic lesions and deformities. They are also developing a DNA probe¾a genetic marker for the fungus¾that they will use to detect if the fungus is, in fact, penetrating the reptile’s skin on a microscopic level.
Another mystery is why this fungus is striking now. Could it be teaming up with another pathogen to deliver a one-two punch to the reptiles, much as some scientists think the nosema fungus might work together with viruses and pesticides to kill honeybees? Tom French, an assistant director at Massachusetts Fish and Wildlife, says a virus could be weakening the immune system of snakes, allowing the fungus to take hold. Because the snakes often emerge from hibernation in spring with more severe infections, he says, it’s possible that the animals carrying a virus might be more vulnerable to types of fungi that thrive in the cool, damp dens where snakes spend the winter.
Meanwhile, Lorch and his colleagues are trying to determine whether or not the pathogen is invasive to North America, or if it’s a native fungus that has suddenly become more virulent—and if so, why? “If O. ophiodiicola and SFD are native to North America,” he says, “then it’s possible that environmental events such as climate change could be exacerbating the disease.” Either way, Lorch notes, the environment always plays a role in disease ecology. But at least for now, the reason behind the epidemic has slithered from our grasp.
Images: D.E. Green, USGS National Wildlife Health Center
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