A fungus long suspected of killing more than a million bats in the US since 2006 has been pronounced guilty after a series of experiments on captive animals. The tests confirm that "white nose syndrome", so called because it leaves fuzzy white smudges on the muzzles of its victims, is caused by the Geomyces destructans fungus.
When researchers infected 29 captive little brown bats (Myotis lucifugus) with lab-grown samples of the fungus, they all developed the disease, showing the tell-tale signs and symptoms about three months after infection. None of the 34 controls, which were not infected with the fungus, developed the condition.
Through complementary experiments in which the researchers housed 25 infected bats together with 18 healthy bats, they demonstrated that bats catch the syndrome from each other through physical contact. It cannot spread through the air: healthy bats did not pick up the infection when housed near to, but physically isolated from, diseased bats.
The experiments confirm what many experts had suspected, and rule out the possibility that the fungus preys on sick animals but does not actually cause the disease.
"The discovery allows us to focus our research efforts to develop management and control strategies," says David Blehert of the National Wildlife Health Center, part of the US Geological Survey in Madison, Wisconsin, who led the research team. "Unfortunately, there's no silver bullet to kill the fungus."
Hard to prevent
Most potential solutions have drawbacks, explains Blehert. Applying fungicides in caves might harm plants and other animals living there, and this would have to be done year after year to keep the fungus at bay. Even culling bats in infected caves wouldn't work, because some infected bats would escape and return, or spread the fungus elsewhere.
Of all the possible solutions, vaccination might provide the best hope, says Blehert, because it would potentially give bats lifelong immunity. He points out that wild foxes, skunks and racoons have been successfully vaccinated against rabies by dropping vaccine-baited food into their habitats from planes.
Earlier this year, a study found that the Geomyces destructans fungus found in US bats is almost identical to one in Europe to which most native bats seem to be resistant. Finding out what makes the European bats resist the fungus could help find ways to protect their US cousins.
The earlier study also raised the possibility that the US fungus originated in Europe and was inadvertently brought to the US by humans. The US Fish and Wildlife Service says that existing precautions issued by the US Geological Survey to stop humans spreading the fungus any further remain essential.
The wildlife service has called for proposals to follow specific research objectives designed to help the US bats. These include identifying the times of the year when the fungus spreads most easily, the factors that affect bat survival, the features of bat-cave environments that might potentially be altered to obstruct spread, and screening for other microbes that may kill the fungus or hamper transmission without harming bats.
Journal reference: Nature, DOI: 10.1038/nature10590
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