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LEWISBURG, Pa. - A team of scientists including Bucknell biology professor DeeAnn Reeder has identified the deadly fungus that causes white-nose syndrome in bats. The finding is a critical milestone in the effort to prevent extinction of the nocturnal creatures in eastern North America.
In a study conducted at the National Wildlife Health Center in Madison, Wis., the researchers showed that Geomyces destructans, the tell-tale white fungus found on sick bats, led to white-nose syndrome in otherwise healthy hibernating bats - both those artificially infected with the fungus and those that shared a hibernation space with bats that contracted the condition naturally, according to a paper published in Nature magazine Wednesday. || See full text of paper.
"For a long time, a lot of us - myself included - said fungal infections don't kill mammals, so that can't be what's killing the bats," said Reeder, an associate professor who studies the hibernation patterns of bats. "But it turns out that because of the bat's unique hibernation cycle and the nature of the fungus, it does kill them. The big question now is: Can we prevent extinction?"
Searching for answers
White-nose syndrome was discovered in hibernating bats in the winter of 2006 by a state wildlife biologist and cavers in the state of New York. It since has spread throughout New England and into the Mid-Atlantic states. Reeder, an ecophysiologist, became involved in the research in 2008, when she began to study the hibernation patterns of bats in her laboratory at Bucknell. She and several collaborators have tried drug treatments, including the active ingredients from some over-the-counter antifungal creams for athlete's foot, but nothing has been able to eradicate the disease, she said.
Six species of bats have been affected so far, notably the little brown bat, which is the most common kind of bat in the Northeast. Bats are beneficial to the ecosystem in part because they eat a significant number of insects, including disease-ridden mosquitoes and crop pests. Reeder estimates the million bats that died would have eaten 694 tons of insects last year.
Bats with white-nose syndrome have been found dead or starving, flying erratically during the day and in cold temperatures, weeks before they normally emerge from hibernation. Not all of the infected bats have visible white fungus. Other symptoms include extreme weight loss, depleted fat reserves or the inability to awaken from hibernation. Scientists have suspected that the fungus, a virus, bacteria or a parasite caused the disease and that the condition is worsened by environmental factors.
Working against extinction
Although scientists have yet to find a cure for white-nose syndrome, identifying a fungus as the cause allows researchers to focus on which bats are most likely to survive white-nose syndrome and work to improve their chances. One idea is to make mines where certain bats hibernate colder so that the fungus is not able to thrive, Reeder said.
"The more we understand this disease triangle - how hosts, pathogen and environmental factors interact - the more we can say this species will get it and that species will not," Reeder said. "There are certain things about this host and certain things about this pathogen that came together. You have a host that in winter is immune-suppressed and metabolically inactive. You have a cold-loving pathogen that grows best in 5 to 14 degrees and an environment where bats roost that is between 2 and 12 degrees. If you were trying to make a pathogen to kill bats, this is exactly how you would design it."
One frustrating aspect of Geomyces destructans is that, as a cold-loving fungus, it is able to survive in extremely cold conditions and without a host. Therefore, the disease is not always spread from bat to bat. One ray of hope is that European bats infected with the fungus are not dying at the rate North American bats have, indicating the condition may have long passed through their populations and the remaining bats have adapted to it, Reeder said. Further studies will be needed to determine differences in the makeup and behavior of North American versus European bats to find out why the European bats fare better with the disease.
In the latest study, researchers housed healthy little brown bats at the National Wildlife Health Center under hibernation conditions and inoculated the wings with purified fungus. Most of the exposed bats developed legions consistent with white-nose syndrome after 83 days. All were positive with white-nose syndrome after 102 days.
Healthy bats also were placed in the same hibernation chamber with infected bats to determine if the condition is transmitted from bat to bat. About 89 percent of the healthy bats had white-nose legions after 102 days.
In addition to identifying the cause, the study showed that healthy bats typically die several months after they are infected with the white-nose fungus, when they are deep in hibernation and have been in an environment conducive to the survival of the fungus.
The project was funded by the U.S. Geological Survey, the U.S. Fish and Wildlife Service, Bat Conservation International and the Indiana State University Center for North American Bat Research and Conservation.
Graduate student Jeffrey M. Lorch of the University of Wisconsin-Madison and his mentor, David S. Blehert of the National Wildlife Heath Center were the lead researchers on the study. Reeder was the bat hibernation physiologist who helped design and execute the study. Other collaborators were:; Carol U. Meteyer and Anne E. Ballmann of the National Wildlife Health Center, U.S. Geological Survey; Melissa J. Behr of the Wisconsin Veterinary Diagnostic Laboratory; Justin G. Boyles of the University of Tennessee; Paul M. Cryan; of Fort Collins Science Center in Colorado; Alan C. Hicks of the New York Department of Environmental Conservation; Jeremy T. H. Coleman of the U.S. Fish and Wildlife Service in Hadley, Mass.; and David N. Redell of the Wisconsin Department of Natural Resources.
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