Between 5.7 and 6.7 million bats have died in North America due to a fungus known as white-nose syndrome (WNS) since the disease first appeared in 2006, US authorities said on Tuesday.
The count is a vast increase over the one million bats believed dead according to the last estimate in 2009, and in some areas has meant that nearly all of the bat population is gone, wildlife expert Jeremy Coleman told AFP.
"In states like New York and Vermont and southern Ontario, we anticipate that the overall population is probably impacted on the order of 90-plus percent," said Coleman, national white-nose syndrome coordinator at the Fish and Wildlife Service.
The figures were compiled using data from state biologists and mathematical models to project losses across geographical areas where the disease is known to have spread.
"This startling new information illustrates the severity of the threat that white-nose syndrome poses for bats, as well as the scope of the problem facing our nation," said Fish and Wildlife Service Director Dan Ashe.
"Bats provide tremendous value to the US economy as natural pest control for American farms and forests every year, while playing an essential role in helping to control insects that can spread disease to people."
Bats are in important natural pesticide worth at least 3.7 billion dollars per year to farmers, a recent study calculated.
The first known outbreak of WNS has been traced to a colony of bats in upstate New York, and has spread 2,000 kilometers (1,200 miles) across the United States and into Canada.
It has now been documented in 16 states and four Canadian provinces.
The syndrome is particularly lethal for winter colonies of species that hibernate, including little brown bats, northern long-eared bats and the endangered Indiana bat, according to the United States Geological Survey.
A study published late last year confirmed that the disease is caused by a fungus called Geomyces destructans, but experts are stumped as to how to stop it.
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