A fungal disease that has killed millions of North American bats is spreading and now has been detected in half of the United States, officials said Thursday.
Wildlife agencies in Michigan and Wisconsin said they had confirmed diagnoses of white-nose syndrome in tested bats, further evidence of the ailment's rapid expansion since it first was documented in a cave near Albany, N.Y., in 2006. Cases have turned up in most states east of the Mississippi River, with Georgia and Alabama joining the list in March, and as far west as Missouri and Arkansas.
Officials said the latest discoveries were no surprise but a cause for sadness, acknowledging they had no cure and could take only limited steps to protect the winged mammals that provide an enormous economic and ecological benefit by feasting on nuisance insects that gobble crops and trees.
"We face the loss of multiple bat species and the benefits they provide to our ecosystems and our people," said Erin Crain of the Wisconsin Department of Natural Resources.
White-nose syndrome is named for the fuzzy spots it plants on victims' muzzles, wings and tails. It doesn't affect people or other animals but repeatedly interrupts bat hibernation, sapping their energy and fat stores, which can cause starvation and dehydration.
More than half of the 45 bat species in the U.S. hibernate during winter. Many seek out caves or mines, an ideal environment for spreading the killer fungus as bats clump together on the moist walls.
Some might survive if they contract the illness late enough in winter. But the refuge could be a death trap for those that return the following year. And some will move on to other enclosures and infect them — particularly during fall mating season when huge flocks of bats sweep in and out of caves and mines, said Allen Kurta, an Eastern Michigan University scientist.
No one has come up with a treatment that would kill the fungus but not the bats, said Dan O'Brien, a wildlife veterinarian with the Michigan Department of Natural Resources. Another seemingly insurmountable challenge would be producing enough medication and getting it to the animals.
"You'd have to have enough to treat all the bats out there to alter the course of the outbreak," O'Brien said.
Crain said researchers are looking into disinfecting hibernation spots, making them cooler or drier to prevent the fungus from blooming, and even cleaning individual bats.
One step that can be taken is to prevent humans from spreading the fungus, officials said. When people explore caves and abandoned mines, the spores often stick to their clothes and climbing gear.
That may explain how the disease reached the U.S., O'Brien said. It's believed to have come from Europe, which has different bat species that are not greatly affected. The New York cave where it first appeared is popular with explorers.
The Michigan agency is developing an order barring entry to caves and abandoned mines on state property. It's also placing gates at the entrances of bat hibernation sites. The structures have slats wide enough for bats to get in and out but too narrow for people.
Twenty-two of the 27 largest hibernation spots in Michigan have been gated, O'Brien said. They host an estimated 272,000 bats.
Wisconsin adopted rules in 2010 designed to stave off white-nose syndrome. In addition to listing four cave bat species as threatened, they declare caves on state property off-limits during winter and require cave and mine visitors to decontaminate their shoes and equipment.
Additionally, Wisconsin prohibits gear in its caves that out-of-state residents have used elsewhere. The state has spent about $5,400 in federal money on equipment that spelunkers from other states can use at three commercial caves.
Eric McMaster, who received some of the money for his Crystal Cave in Spring Valley, said he doesn't believe the discovery of white-nose will change his operations much.
"We have it in Iowa, we have it in Minnesota, we have it up in Canada," he said. "It's just inevitable. The fungus doesn't respect state boundaries."
Only a few cases of the disease have been found in the two states, but officials said large-scale die-offs might not be far away.
A U.S. Geological Survey lab in Madison, Wis., confirmed that at least two bats from a mine in Grant County in the southwestern corner of the state were infected. In Michigan, the fungus was found in five bats from three counties: Alpena in the northern Lower Peninsula and Dickinson and Mackinac in the Upper Peninsula.
The disease has been confirmed in 25 states and the fungus has been found in three others, according to the U.S. Fish and Wildlife Service, which estimates that more than 6 million bats have died.
A 2011 study led by Justin Boyles of Southern Illinois University calculated that bats save the agricultural economy $22.9 billion a year by gobbling crop-damaging insects and reducing the need for pesticides. They also eat mosquitoes, some of which carry West Nile virus.
Richmond reported from Madison, Wis.