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Culprit behind bat scourge confirmed

October 26, 2011 By Susan Young This article courtesy of Nature News.

A cold-loving fungus is behind an epidemic decimating bat populations in North America.

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Researchers have confirmed that a recently identified fungus is responsible for white-nose syndrome, a deadly disease that is sweeping through bat colonies in eastern North America.

The fungus, Geomyces destructans, infects the skin of hibernating bats, causing lesions on the animals' wings and a fluffy white outgrowth on the muzzle. When white-nose syndrome takes hold of a hibernating colony, more than 90% of the bats can die (see Disease epidemic killing only US bats). The disease was first documented in February 2006 in a cave in New York, and has spread to at least 16 other US states and four Canadian provinces.

The culpability of G. destructans for this sudden outbreak was thrown into question when the fungus was found on healthy bats in Europe, where it is not associated with the grim mortality levels seen in North America1. Some proposed that the fungus was not the primary cause of the catastrophic die offs, and that another factor — such as an undetected virus — must be to blame. But a study published today in Nature2 reveals that G. destructans is indeed guilty.

"The fungus alone is sufficient to recreate all the pathology diagnostic for the disease," says David Blehert, a microbiologist at the National Wildlife Health Center in Madison, Wisconsin, and senior author on the report.

Bat-to-bat spread

Blehert and his colleagues collected healthy little brown bats (Myotis lucifugus) from Wisconsin, which is well beyond the known range of white-nose syndrome. They infected the bats by direct administration of G. destructans spores to the skin or by contact with infected bats from New York. By the end of the 102-day experiment, the tell-tale white fungus was growing on the muzzles and wings of all of the directly infected Wisconsin bats and 16 of the 18 exposed to sick bats.

This is the first experimental evidence that white-nose syndrome can be passed from bat to bat, and is very worrying from a conservation point of view because bats huddle together in large numbers in caves and mate in large swarms, says Emma Teeling, a bat biologist at University College Dublin in Ireland. "If a bat has this fungus on them, it's going to spread quickly throughout the population," says Teeling, who was not involved with the study. "It's like a perfect storm."

The infected Wisconsin bats did not die during the experiment, which may be due to the limited timeline of infection, the authors suggest. Although the study does not directly show that a healthy bat will die from infection with G. destructans, the results did show that the fungus alone was sufficient to cause lesions diagnostic of white-nose syndrome to form on previously healthy bats, indicating that the fungus is the cause of the deaths so often associated with white-nose syndrome in the wild.

To stop a scourge

Since it first appeared, white-nose syndrome has behaved like a novel pathogen spreading from a single origin through a naive population, says Jonathan Sleeman, director of the National Wildlife Health Center, who was not involved in the study. Proof that G. destructans is the primary cause of white-nose syndrome will "help us focus our actions or management efforts into the future", he says.

Although little can be done to control the spread of the disease through bat-to-bat transmission, the US Fish and Wildlife Service (FWS) has asked people to stay out of caves in and near affected areas, and has closed some caves on agency-managed land.

On 21 October, the FWS announced that up to $1 million in funding will be made available for research on white-nose syndrome. Projects covering topics such as how the fungus proliferates within caves and mines, and the potential for biological means or environmental manipulations to improve bat survival, are among the service's top priorities.


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