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White-nose syndrome (WNS) is a poorly understood disease associated with the deaths of at least 5.7 million to 6.7 million North American bats. The condition, named for a distinctive fungal growth around the muzzles and on the wings of hibernating bats, was first identified in a cave in Schoharie County, New York in February 2006. It has rapidly spread, and as of 2013, the condition had been found in over 115 caves and mines ranging mostly throughout the Northeastern U.S. and as far south as Alabama and west to Missouri and into four Canadian provinces.
It is believed that Pseudogymnoascus destructans (formerly Geomyces destructans) is the sole cause of the disease. Direct microscopy and culture analyses demonstrated that the skin of the WNS-affected bats is colonized by a psychophilic fungus that is phylogenetically related to Geomyces spp., but with a conidial morphology distinct from characterized members of this genus. This report characterizes the cutaneous fungal infection associated with WNS. No obvious treatment or means of preventing transmission is known, and the mortality rate of some species has been observed at 95%.
Due to the disease the US Fish & Wildlife Service (USFWS) has called for a moratorium on caving activities in the affected areas and strongly recommends that any clothing or equipment used in such areas be decontaminated after each use. The National Speleological Society maintains an up-to-date page to keep cavers apprised of current events and advisories.
With the mortality rate in some caves exceeding 90%, WNS has greatly decreased bat populations in North America and has the potential to cause the extinction of several species. There are currently nine hibernating bat species confirmed with infection of Pseudogymnoascus destructans, and at least five of those species have suffered major mortality. Some of those species are already listed as endangered on the U.S. endangered species list, including the Indiana bat, whose primary hibernaculum in New York has been affected, and the big-eared bat (Corynorhinus townsendii virginianus), the official state bat of Virginia. The once-common little brown bat has suffered a major population collapse and may be at risk of rapid extinction in the northeastern U.S. within 20 years due to WNS. Alan Hicks with the New York State Department of Environmental Conservation has described the impact as "unprecedented" and "the gravest threat to bats...ever seen."
Beyond the direct effect on bat populations, WNS has broader ecological implications. The Forest Service estimates that the die-off from white-nose syndrome means that at least 2.4 million pounds of insects (1.1 million kg) will go uneaten and become a financial burden to farmers, possibly leading to crop damage or having other economic impact in New England.
Comparisons have been raised to colony collapse disorder, another poorly understood phenomenon resulting in the abrupt disappearance of Western honey bee colonies, and with chytridiomycosis, a fungal skin disease linked with worldwide declines in amphibian populations.
Biologists are investigating the geographic extent of the outbreaks and collecting samples of affected bats. Bucknell University professor DeeAnn Reeder, one of the foremost experts on White-Nose Syndrome, expects it will continue to spread across the United States, and drive some species to extinction. "While a number of researchers from multiple academic disciplines are now working on WNS research, and while we are beginning to understand how this fungus (Pseudogymnoascus destructans) is killing bats, we are really struggling in our attempts to control the spread," Reeder said. A geographic database is being developed to track the location of sites where WNS has been found, collecting information at each site in regards to the number of bats affected.
The U.S. Fish and Wildlife Service is also partnering with the Northeastern Cave Conservancy to track movements of cavers that have visited affected sites in New York. It has also advised closing caves to explorers in 20 states, from the Midwest to New England. This directive will soon be extended to 13 southern states. As one Virginia scientist stated, "If it gets into caves more to our south, in places like Tennessee, Kentucky, Georgia and Alabama, we’re going to be talking deaths in the millions.". In March 2012, WNS was discovered on some tri-color bats (Perimyotis subflavus) in Russell Cave in Jackson County Alabama.
Recent research has found that the fungus may respond to typical human anti-fungal treatments. More studies are being undertaken to determine how best to use this knowledge.
The fungus Pseudogymnoascus destructans is believed to be the primary cause of WNS. A 2011 study found that 100% of healthy bats infected with the fungus cultured from infected bats exhibit lesions consistent with the disease. Pseudogymnoascus destructans can only grow in low temperatures, in the 4 to 15 °C range (39–59°F). The fungus will not tolerate temperatures above 20 °C (68 °F) and appears to be adapted to attacking hibernating bats. Infection causes bats to rouse too frequently from torpor (temporary hibernation) and starve to death through excessive activity. The symptoms associated with WNS include loss of body fat, unusual winter behavior (including flying), damage and scarring of the wing membranes, and death.
Although early laboratory research placed the fungus in the genus Geomyces, later phylogenic evaluation revealed this organism should be reclassified. The genera Geomyces and Pseudogymnoascus are closely related and found in the family Pseudeurotiaceae, but P. destructans was found to be most closely related to the "Pseudogymnoascus" species, indicating that its name should be changed to Pseudogymnoascus destructans.
The disease was first reported in January 2007 in some New York caves. It spread to other New York caves and into Vermont, Massachusetts, and Connecticut in 2008. In early 2009 it was confirmed in New Hampshire, New Jersey, Pennsylvania, West Virginia and, in March 2010, Ontario, Canada, and Middle Tennessee. In 2012, new cases showed up in northeastern Ohio, and Acadia National Park in Maine. New confirmed cases appeared in 2013 in Georgia, South Carolina, and Illinois.
There is consensus among researchers that bat-to-bat transmission is the predominant factor in the spread of the disease. A laboratory experiment suggests that physical bat-to-bat contact is required for the spread of the disease. The same study found that bats in mesh cages adjacent to infected bats did not contract the fungus, implying that the fungus is not airborne, or at least is not spread from bat to bat through the air.
The role of humans in the spread of the disease, and the transmission of the fungus from Europe, is debated. The occurrence of the same fungus in healthy bats in Europe suggests that the fungus originated in Europe, where some bats acquired immunity and was somehow transmitted to bats in North America which lack immunity to the disease. This aspect of the geographic spread led some officials to argue that humans may also transmit WNS from infected sites to clean sites, probably on clothing and equipment.
The fungus Pseudogymnoascus destructans, or a closely related species of fungus, has been found in soil samples from infected caves and suggests that it can be transported from cave to cave by soil, such as that carried by human clothing. Precautionary decontamination methods are being encouraged to inhibit the possible spread of spores by humans. The WNS Decontamination Team, a sub-group of the Disease Management Working Group, published a national decontamination protocol on March 15, 2012. They revised the protocol on June 25, 2012 and will continue updates as needed.
Cave management and preservation organizations have been requesting that cave visitors limit their activities and disinfect clothing and equipment that has been used in possibly infected caves. In some cases, access to caves is being closed entirely.