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article imageFighting a fungus that's killing America's wild snakes

By Karen Graham     Nov 13, 2014 in Environment
Since the early 2000s, a fungal infection has been devastating wild snake populations in the Midwest and eastern U.S.. The impact of the disease on the ecosystem has taken on greater significance, prompting further studies to find a cause and cure.
The spread of Snake Fungal Disease (SFD) has resulted in a number of extensive studies being done. The latest study, led by Matthew Allender, a clinical assistant professor of zoo and wildlife medicine at the University of Illinois at Urbana-Champaign and his colleagues, has resulted in a faster, more accurate means of testing for the fungus.
The study was presented at the 2014 annual meeting of the Mycological Society of America held in June at the Kellogg Center, Michigan State University, East Lansing. “We need people to know that they don’t have to anesthetize an animal to collect a biopsy sample or, worse yet, euthanize snakes in order to test for the infection,” said Allender. “Now we can identify the infections earlier, we can intervene earlier and we can potentially increase our success of treatment or therapy.”
This eastern rat snake (Pantherophis alleghaniensis) has opaque eyes and hard  crusty scales on its ...
This eastern rat snake (Pantherophis alleghaniensis) has opaque eyes and hard, crusty scales on its snout, telltale signs of snake fungal disease.
D. E. Green/USGS National Wildlife Health Center
SFD is thought to be caused by Ophidiomyces ophiodiicola, a fungus that has repeatedly shown up in infected snakes. Widespread reports of the disease began showing up at the USGS National Wildlife Health Center (NWHC) and other diagnostic laboratories in 2006. At that time, nine states, including Illinois, Florida, Massachusetts, Minnesota, New Jersey, New York, Ohio, Tennessee, and Wisconsin were reporting widespread infection with SFD in wild snake populations.
The new test uses a quantitative polymerase chain reaction (qPCR). This makes the fungal DNA easier to identify as well as allowing scientists a ready means of identifying the extent of the infection. “Our qPCR is more than 1,000 times more sensitive than conventional PCR,” Allender said. “We can know how many [fungal spores] are in a swab, and then we can start to treat the snake and we can watch to see if that number is going down.”
A northern water snake (Nerodia sipedon)  which was captured in 2009 from an island in western Lake ...
A northern water snake (Nerodia sipedon), which was captured in 2009 from an island in western Lake Erie, Ohio. The snake has crusty and thickened scales over raised blisters, a sign of snake fungal disease.
D. E. Green/USGS National Wildlife Health Center
The course of the disease usually results in death for the snake. Clinical signs include scabs and a crustiness on the scales, nodules under the skin, as well as separation of the skin from the underlying tissues. Eventually, the eyes cloud over and the head sometimes swells. Deep, subcutaneous lesions develop. It is not a pretty sight, and must be very painful.
At first, researchers found infections only in rattlesnakes and other vipers, "which is not good because those snakes tend to be the most endangered already," Allender said. "But now the disease has also surfaced in nonvenomous snakes, including snakes that are both solitary and social." Allender said this suggests the snakes can catch the disease from each other as well as from fungus in the soil. While the infection can begin by several routes of entry, Allender says, "They just have to have contact with the fungus."
Allender says it is unclear just how widespread the disease is now. Researchers do know that 14 species of snakes are now affected by SFD, both venomous and non-venomous. In a 2011 study published in the journal Biological Conservation, the fungus was linked with a 50 percent drop in the timber rattlesnake population in New Hampshire between 2006 and 2007. This is particularly significant because New Hampshire has just one population of its endangered timber rattlesnake left in the state.
The dark coloration of the timber rattlesnake in New Hampshire helps in camouflaging it from predato...
The dark coloration of the timber rattlesnake in New Hampshire helps in camouflaging it from predators.
The identification of this disease, as well as figuring out how to control or eradicate it is vitally important. The decline of snake populations from anthropogenic means rarely can be attributed to any one cause. There are a variety of factors involved, including habitat loss, inbreeding, disease, and climate change. In the case of New Hampshire's last remaining population of timber rattlesnakes, it was discovered that increased urbanization had led to the demise of many populations of the viper across the state.
The remaining population of timber rattlesnakes was then further diminished due to inbreeding. Add to this insult the effects of climate change. In 2009, New Hampshire experienced an extremely high amount of summer rainfall. This resulted in the timber rattlesnake population getting the SFD, further resulting in a 50 percent mortality rate.
The decline in our wild snake populations affects all of us. Snakes prey on mice and rats. Some prey on frogs and fish. The snakes are in turn, prey to other creatures. Putting a crimp in the ecological balance will impact on biodiversity, sometimes in unexpected ways.
More about snake fungal disease, New hampshire, Timber rattlesnake, Ecological impact, Climate change
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