The U.S. Fish & Wildlife Service this week advised people to stay out of caves in the Northeast to hopefully slow the spread of white-nose syndrome (WNS), a deadly fungal infection blamed for the deaths of as many as half a million bats over the past two years.

The fungus grows on bats' facial skin and flight membranes, possibly causing them to starve. In caves where it has been observed, bats have suffered morality rates ranging from 75 to 100 percent.

WNS appears to be transmitted from bat to bat, but because the condition has spread so quickly, it seems that something else may be helping the fungus move from cave to cave. "We suspect that white-nose syndrome may be transmitted by humans inadvertently carrying WNS from cave to cave where bats hibernate," FWS Northeast Regional Director Marvin Moriarty said in a statement.

Justin Boyles, a biologist at Indiana State University, Terre Haute, agrees. "There is growing circumstantial evidence that WNS is being moved around by humans," he says. "It has made some big jumps and has shown up in a couple of caves that are visited relatively heavily by humans. That alone doesn't rule out that bats could be the only route for transmission, but it is suspicious." 

So far, there isn't any conclusive evidence that people might be affected by the fungus or are responsible for its spread. (An anonymous spelunker said he found the explanation unlikely in a post on ProMEDmail, an e-mail alert that monitors emerging infectious diseases around the world, earlier this month.) But the FWS hopes the voluntary breather from caving will help keep the toll from climbing and give biologists time to find a cure. Among the bats afflicted: the endangered Indiana bat (Myotis sodalis).

The advisory affects the eight states where WNS has been observed (New York, Vermont, Massachusetts, Connecticut, New Hampshire, New Jersey, Pennsylvania, and West Virginia), as well as adjacent states like Maine, Kentucky and Ohio.

"I think this advisory is a good, proactive move on the part of FWS," Boyles says. "Hopefully, we will find evidence that humans aren't spreading WNS and then FWS can back down from the full scale advisory, but until then, I think we're better safe than sorry."

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