Fungus endangers U.S. bat colonies

By: Nicole Angeli

Posted: 4/30/09

Bat populations along the east coast of the United States have been declining sharply in recent years, most likely due to a mysterious fungus.

The U.S. Fish and Wildlife Service placed a moratorium on human activities in caves as of March 26 in 17 states, which are home to bats with a deadly and poorly understood condition which has been termed White-Nose Syndrome, for the characteristic white fungus that grows on the noses of infected bats.

White-Nose Syndrome (WNS) causes up to 90 percent mortality in some infected caves, and overall more than a 75 percent population decline over two-year periods at infected sites. This translates into the death of hundreds of thousands of bats. First recorded in upstate New York during the winter of 2005-2006, WNS has spread quickly, infecting caves from Vermont to Virginia.

In addition to being transmitted from bat to bat, the infection has been spreading between caves that are geographically isolated from each other in a pattern known as "leapfrogging," which suggests cavers may be aiding the transmission of the disease between caves. This hypothesis is further supported by the fact that many of the infected caves are popular caving sites.

The fungus that has been collected from bats presenting with symptoms was first described in October 2008, but more research is needed to correlate the fungus to the deaths, as well as produce a timely solution in ending bat demise.

The U.S. Fish and Wildlife Service has expressed concern that research efforts in natural caves will merit more risk than helpful results for bats. Scientists in Wisconsin have been replicating cave conditions to determine the experimental rate at which the fungus is transmitted from cave to cave and bat to bat.

Cave condition replications are currently a good alternative to performing research in natural caves when research into developing human and environmental disinfectant protocols have not yet been standardized.

The cave closures, which are intended to stop the spread of the disease, are being practiced in close collaboration with the caving community. The National Speleological Society, a prominent caving organization, and other local caving groups have mobilized to raise funds, increase public awareness and keep people out of caves to give hibernating bats a fighting chance when they emerge this spring.

Hypotheses that explain the aggressive spread of WNS suggest that affected bats may become predisposed to the disease because of insufficient fat reserves for hibernation, caused by poor summer feeding and the bio-accumulation of agricultural pesticides. These factors decrease immune system strength and make the bats much more susceptible to the fungus.

Bats present with symptoms that include average body weight reduction, emaciation of white and brown fat reserves, flying during the day and moving to colder areas of the caves in which they hibernate. Bats with WNS have been observed staying in cave areas which are several degrees colder than the normal hibernation space, dangerous during the long winter when energy needs to be carefully conserved.

Furthermore, this type of fungus, of the Geomyces genus, normally thrives in colder environments, exacerbating the bats' condition. Scientists are not yet sure what makes the fungus so lethal to these bat colonies. Some have hypothesized that a combination of environmental and biological factors are at work.

Most of the bats that have been afflicted by WNS die from starvation, which suggests that the fungus causes the bats to expend too much energy during the hibernation period.

Bats are crucial to their ecosystems for their roles in pollination, seed dispersal and insect control. As the second-most diverse mammal in the world, bat populations have evolved to fulfill a range of ecological community functions.

For now, a challenging puzzle remains to solve the mystery of White-Nose Syndrome causation and determine the most effective treatment for bat colonies.