White-nose syndrome, which causes bats to develop white patches on their muzzles and other parts of their bodies during winter hibernation, has been detected in Ontario, Quebec, New Brunswick, Nova Scotia and 16 U.S. states. (Ryan von Linden/New York Department of Environmental Conservation/Associated Press)

The white-nose syndrome epidemic that has killed more than five million bats in Eastern Canada and the U.S. in recent years is likely caused by a fungus recently introduced from Europe by humans, a Canadian-led study has found.

The lab experiments led by biologists Lisa Warnecke and Craig Willis at the University of Winnipeg also confirm details of how the fungus kills the bats. The study, which also involved researchers from Saskatchewan, the U.S. and Germany, was published Monday in the Proceedings of the National Academy of Sciences.

White-nose syndrome, first detected in North America in 2006, causes bats to develop white patches on their muzzles and other parts of their bodies during winter hibernation. Affected bats appear to wake up from hibernation early and weakened, and they often die.

The syndrome was previously linked to infection with the fungus Geomyces destructans. But scientists weren't sure why North American bats were dying in great numbers, while their European counterparts were not, since the fungus is found in both places. Two possibilities were that:

• The fungus is native to both North America and Europe, but recent changes in the environment or a genetic mutation have made the North American strain more deadly.
• The fungus is an invasive species in North America recently introduced from Europe, so European bats have immunity and North American bats do not.

Warnecke and Willis tested both possibilities in the lab using little brown bats, which were one of the most common bat species in North America before being decimated by white-nose syndrome. Now Canada is considering putting the bat on the endangered species list.

'This thing is probably our fault.'—Craig Willis, University of Winnipeg

The researchers infected bats with either the European or the North American strain of the fungus and observed them during hibernation.

"If we were dealing with a mutant in North America … we'd predict that the North American fungus should be way nastier for our bats than the European fungus," Willis said. "What we actually observed was the European version was even a little bit nastier."

That is consistent with the fungus being an invasive species that has been able to sweep through a population with little immunity to the unfamiliar pathogen.

Willis believes the fungus was likely introduced by people, since the first North American cases of white-nose syndrome were reported in 2006 at a cave in New York State that attracts thousands of human visitors per year. He suggested a tourist may have wandered in with the fungus attached to his or her boots.

"This thing is probably our fault," Willis said, "which to my mind means we have an obligation to try and figure out what's happening and hopefully fix it or… at least try to figure out ways to minimize the negative consequences."

In the meantime, he said, it highlights the fact that people should be exceptionally careful about not carrying invasive species with them when they are moving from site to site while conducting research or caving recreationally.

Infected bats run out of fat

The lab experiments also confirmed scientists' previous hunches that the fungus can indeed make bats really sick, causing the bats to warm up and wake up during hibernation, depleting the fat stores they need to survive the winter.

Bats normally conserve energy during hibernation by lowering their body temperature, but infected bats warmed up to normal body temperature three to four times more often as healthy bats toward the end of hibernation.

After four months of hibernation, healthy bats still had lots of fat left, Willis said, but the infected bats "were in really rough shape."

Some died on their own and others had to be put down.

"They couldn't warm up from hibernation on their own," Willis said. "They were completely out of fat at that point."

Previous lab experiments by other researchers had not found such a dramatic difference between healthy and infected bats. Willis suggested that the higher humidity in his experiment may have made the difference. He added that the bat species that have suffered the worst declines from white-nose syndrome are also the ones that like the wettest environments.

Willis said the research suggests that future efforts to protect bats should focus on those environments.

In the meantime, he said, there is still lots of research that needs to be done into how the disease is spread and how to manage that spread.

The U.S. Department of Fish and Wildlife reported in January that 5.7 million to 6.7 million bats in North America have died from white-nose syndrome. It has been detected in Ontario, Quebec, New Brunswick, Nova Scotia and 16 U.S. states.