U.S. scientists say they've identified the cause of a mysterious die-off of snakes of several species in the East and Midwest.

They had zeroed in on a condition known as snake fungal disease (SFD) beginning in 2005, when some snakes in New Hampshire started dying from severe skin infections.

When the disease, which can cause ulcers, blisters and thickened skin, spread to nine states and affected at least seven different snake species, researchers increased their efforts to identify the exact fungal variety behind the increase in SFD deaths.

SFD has been has been found in snake species in Illinois, Wisconsin, Ohio, Minnesota, Massachusetts, New Jersey, New York and Tennessee, researchers with the U.S. Geological Survey say.

The culprit is a fungus known as Ophidiomyces ophiodiicola, they report in the journal mBio.

They say they've determined how the disease progresses in infected snakes, a finding that could lead to strategies to treat infected snakes and combat the fungus affecting vulnerable snake populations.

Snakes in the wild are important predators of pests that can damage or destroy agricultural crops and of rats that can harbor disease, while providing food for other, larger predatory animals, the researchers note.

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

To confirm their suspicions about O. ophiodiicola, the scientists infected eight corn snakes bred in captivity with the fungus.

In a matter of days, all eight developed lesions and swellings seen in wild snakes with SFD.

A separate control group of snakes not exposed to the fungus did not develop any symptoms and showed no evidence of O. ophiodiicola in their bodies.

The disease in the infected snakes resulted in several potentially fatal behaviors that could increase their risk from predators or put them at risk of starvation, the researchers observed; infected snakes tended to lie in exposed areas of their cages, and some proved reluctant to eat.

"These behaviors are uncharacteristic of healthy snakes and demonstrate how SFD can put snakes at risk in the wild," Lorch says.

Climate change and warming temperature could see an increase in the prevalence of the fungus, he noted, which could "hinder recovery from SFD because snake immunity is highly dependent on environmental conditions."