Scientists have proven that the fungus Geomyces destructans causes white-nose syndrome, a fast-spreading and highly lethal disease of bats.

Research published Oct. 26 in the journal Nature provides the first direct evidence that this fungus is responsible for a disease that is decimating bats in North America.

Research at the USGS National Wildlife Health Center in Madison, by scientists from the U.S. Geological Survey, the University of Wisconsin-Madison, and other institutions, showed that 100 percent of healthy little brown bats exposed to G. destructans developed white-nose syndrome while hibernating in captivity.

The study fulfilled established criteria for proving that a microbe causes an infectious disease: A pure culture of a suspected pathogen is able to infect a host plant or animal, which then develops the clinical signs of the disease, and then the pathogen is re-isolated from the experimentally infected host species.

White-nose syndrome is a skin infection that often begins around the muzzle, but the exact mechanism of mortality is unknown.

“By identifying the causative agent of white-nose syndrome, this study provides information that is critical for developing management strategies to preserve vulnerable bat populations and the ecosystem services that they provide in the U.S. and Canada,” says study author David Blehert, a microbiologist at the Wildlife Health Center, and a honorary fellow at the School of Veterinary Medicine at UW–Madison.

This study could help bat conservation by supporting refinements to disease management strategies, said Jeffrey Lorch, a graduate student in the UW–Madison Molecular and Environmental Toxicology Center, another contributor to the study.

Although the study demonstrated that G. destructans can spread by contact between bats, transmission through the air was not seen. Still, it's likely that the fungus can spread by several mechanisms, Blehert added.

“Virtually all pathogens, especially spore-producing fungi, are spread by multiple routes,” he says. “This is why in an effort to further control the spread of white-nose syndrome, resource-management agencies have implemented universal precautions, including limiting human access to sensitive environments occupied by bats, decontaminating equipment and clothing moved between these environments, and restricting the movement of equipment between sites.”

Insect-eating bats provide ecological services that are estimated to save the U.S. agricultural industry billions of dollars each year in insect-control expenses. However, U.S. bat populations have been declining at an alarming rate since 2006, when white-nose syndrome first appeared in New York state. Since then, the fungus G. destructans has spread southward and westward and has now been found in 16 states and four Canadian provinces.