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White-nose syndrome (WNS) is an emerging 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 from a photo taken in a cave in Schoharie County, New York, in February 2006. It has rapidly spread, and as of September 2014, the fungus has been found in caves and mines throughout the Northeastern U.S. and as far south as Mississippi and west to Missouri and into five Canadian provinces.
The disease is caused by Pseudogymnoascus destructans (formerly Geomyces destructans). Direct microscopy and culture analyses demonstrated that the skin of the WNS-affected bats is colonized by a psychrophilic 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 declines in some species have been >90% within five years of the disease reaching a site.
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 declines in some caves exceeding 90%, WNS has greatly decreased bat populations in North America and has been predicted to cause the extinction of at least one species. Eleven bat species, including three endangered species and one species proposed for endangered species listing, have been affected by WNS or exposed to the causative fungus, Pseudogymnoascus destructans (Pd), but impacts vary widely. Four species have suffered substantial declines. Species already listed as endangered on the U.S. endangered species list, including the Indiana bat, whose hibernaculum in many states has been affected,. Interestingly, the Virginia big-eared bat (Corynorhinus townsendii virginianus), the official state bat of Virginia., and the Gray bat have yet to suffer measurable declines. In contrast, the once-common little brown bat has suffered a major population collapse in the northeastern U.S. and the northern long-eared myotis ("Myotis septentrionalis") has been extirpated from all sites where the disease has been present for >4 years. 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 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[who?], "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-colored bats (Perimyotis subflavus) in Russell Cave in Jackson County Alabama.
The fungus Pseudogymnoascus destructans is 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 grow at temperatures above 20 °C (68 °F). 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 although it was retrospectively detected in a photograph taken in early 2006. 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, Virginia, West Virginia and, in March 2010, Ontario Canada, Maryland, Middle Tennessee, Missouri, and Quebec, Canada. In 2011, the syndrome was confirmed in Ohio, Indiana, Kentucky, North Carolina, Maine, New Brunswick and Nova Scotia. In 2012, Alabama, Delaware and Arkansas were confirmed with the fungus and new cases showed up in northeastern Ohio, and Acadia National Park in Maine. New confirmed cases appeared in 2013 in Georgia, South Carolina, Illinois, and the Canadian Province of Prince Edward Island. On March 28, 2014, white-nose syndrome was detected in a single mine in Grant County Wisconsin by WDNR and USGS staff conducting WNS field research and routine WNS surveillance. The presence of the disease was later confirmed by the USGS National Wildlife Health Center. On April 10, 2014, the Michigan Department of Natural Resources announced that the disease had been found in Alpena County, Mackinac County, and Dickinson County.
The syndrome has been confirmed in 25 states and 5 Canadian provinces, as of April 11, 2014. Three additional states (Iowa, Minnesota, and Oklahoma) were considered suspect for WNS because the causative fungus P. destructans has been detected on resident bats. In May, 2014, after retesting, the Myotis Velifer specimen from Oklahoma and other swabs and samples from the area tested negative, Oklahoma and the Myotis Velifer were removed from the list of White Nose Syndrome suspects.
A laboratory experiment suggests that physical contact is required for the spread of the fungus causing the disease, because bats in mesh cages adjacent to infected bats did not contract the fungus. This implies that the fungus is not airborne, or at least is not spread from bat to bat through the air.
The same species of fungus has been found in healthy bats in Europe, although it's not clear whether it was introduced into North America from Europe or Asia. The role of humans in the spread of the disease is debated. It is likely the fungus was brought to North America by human activities, because no bats normally migrate between Europe and North America, and the fungus was first discovered in New York where there are commercial caves with thousands of visitors per year. In addition, research has shown the fungus can persist on human clothing, and thus could be carried among locations, necessitating a need for Decontamination described below. However, there is little evidence that humans have so far played a role in the spread of the fungus in North America, in that the speed and direction of spread from the initial sites in New York are consistent with what is known about normal bat movement. The lack of long distance spread (e.g. distances greater than 200 km) may be a result of reduced human movement between infected and uninfected sites or decontamination activities or both.
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.
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