Research: Bat-killing fungus arrived from afar

By John Upton

A ripple of bat deaths has grown since 2006 to become millions of Chiroptera deep, stretching out from its New York epicenter into five Canadian provinces and west at least as far as Missouri. The latest state to be affected was Minnesota, where infected bats were discovered in two parks.

The dead bats were all members of species that hibernate — and they succumbed to white nose syndrome. The disease is caused by a fungus that eats away at their wings and faces.

Little brown bats are among the worst affected. These adorably tiny bats were common throughout Eastern America as little as a decade ago, sucking down mosquitoes and other pests during their nocturnal maunders. Now the species appears to be on the verge of being listed as federally endangered.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

Mammals appear to have developed high body temperatures to help stave off infections of fungi. But hibernating bats have a chink in that armor: When they hibernate, their body temperatures plummet. And when most bats hibernate, they huddle together, which helps the fungal infection spread through the slumbering colony.

What caused this fast-moving fungus to suddenly begin attacking bats? Did it go rogue, evolving from a soil eater into a devourer of bat flesh? Or is it an invasive species that arrived from some far-flung place?

A pair of Wisconsin-based U.S. Forest Service scientists studied the DNA of the disease along with that of more than a dozen species of other fungi found growing in bat caves in the eastern U.S. What they found, first and foremost, was that the pathogen was not quite what everybody thought it was.

Scientists have called the disease Geomycetes destructans since it was identified in 2009. But the recent research, described in the journal Fungal Biology, indicates that the fungus is actually a member of the genus Pseudogymnoascus. Hence, it has been reclassified P. destructans.

Of the other species of Pseudogymnoascus fungi sampled in the studied hibernacula, the scientists reported that none were closely related to P. destructans. That’s significant, because it suggests that white-nose syndrome arrived in New York from some other part of the world, perhaps on the shoes of a traveler or shipped in as a few spores with freight.

Researcher Andrew Minnis said the study is part of a wider effort to find a way to protect bats from the fungus. “Once key elements of this [fungus] species’ biology, including mechanisms of pathogenicity, are identified, it will be possible to target them,” he said.

Once it was realized that many related fungi were present in bat caves, but weren’t killing bats, “thoughts arose that these species could be used for comparative purposes — to understand why P. destructans is different,” he said. Following the findings from this study, “further and more informed comparative work can now be performed.”

Confirmed and suspected white-nose syndrome cases. Map updated August, 2013 by the U.S. government.
Confirmed and suspected white-nose syndrome cases. Map updated August, 2013 by the U.S. government.