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Cause of Deadly Disease in Snakes Identified

November 16, 2015

The fungus Ophidiomyces ophiodiicola is the definitive cause of the skin infections in snakes known as snake fungal disease, or SFD, according to U.S. Geological Survey research published today in the journal mBio.

Wild snakes are valuable because they consume pests that damage agricultural crops, prey on rodents that can carry disease and serve as food for many predatory animals. However, some snake populations in the midwestern and eastern United States have declined since 2006 as a result of SFD, which produces thickened skin, ulcers and blisters. New USGS research provides the first direct evidence that O. ophiodiicola causes SFD, documents how the disease progresses and reveals how snakes respond to the infection.

“The loss of certain snake species in eastern North America could have widespread negative impacts on ecosystems,” said Jeffrey Lorch, a USGS National Wildlife Health Center scientist and the lead author of the study. “Pinpointing the SFD-causing fungus can help conserve snake populations threatened by this disease.”

The scientists infected eight healthy captive-bred corn snakes with O. ophiodiicola in the laboratory. Within days after exposure to the fungus, all snakes developed swelling followed by lesions identical to those observed in wild snakes with SFD. These lesions contained the same fungus to which the animals were exposed. Snakes that were not infected in the laboratory did not develop lesions and did not harbor O. ophiodiicola.

Most snakes responded to the fungus by repeatedly molting 15 to 20 days after exposure, but the disease caused potentially lethal behaviors that could increase their risk for predation or starvation in the wild. For example, infected snakes rested in exposed areas of their cages and some snakes were reluctant to eat. The uninfected snakes acted normally.

“These behaviors are uncharacteristic of healthy snakes and demonstrate how SFD can put snakes at risk in the wild,” Lorch said. “Climate change could promote growth of O. ophidiodiicola and hinder recovery from SFD because snake immunity is highly dependent on environmental conditions.”

O. ophiodiicola has consistently been found on snakes with SFD, but this new study is the first to prove that the fungus is the actual cause of the disease. The USGS has confirmed SFD in at least seven species of snakes in nine states: Illinois, Florida, Massachusetts, Minnesota, New Jersey, New York, Ohio, Tennessee and Wisconsin.

For more information on SFD, please visit the USGS National Wildlife Health Center website.

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