White-nose syndrome has invaded Illinois, wildlife officials confirmed Thursday, making it the 20th U.S. state to be infested by the bizarre, bat-killing fungal infection.

The epidemic has been sweeping west since its mysterious 2006 debut in New York, killing about 6 million bats along the way. It's now confirmed in 20 U.S. states and five Canadian provinces, with a mortality rate as high as 100 percent in some bat colonies. It's known to infect seven types of hibernating bats, including two that are endangered, and biologists say it may eventually threaten at least half of all North American bat species.

"We are saddened by the discovery of WNS in Illinois," says Jeremy Coleman, national WNS coordinator for the U.S. Fish and Wildlife Service, in a statement released Thursday. "We will continue to work with our partners to address this devastating disease and work toward conservation of bat species in North America."

The illness had already been discovered west of Illinois last year, both in Iowa and Missouri, so it was likely just a matter of time until it filled in the gap. And since the new cases were found in four different counties scattered across north-central, southwestern and far southern Illinois, there's a good chance it's been hiding there for a while.

"Although its arrival was anticipated, the documented spread of WNS into Illinois is discouraging news, mainly because there is no known way to prevent or stop this disease in its tracks," says Joe Kath of the Illinois Department of Natural Resources. "Pest-control services provided by insect-eating bats in the United States likely save the U.S. agricultural industry several billion dollars a year, and yet insectivorous bats are among the most overlooked, economically important, non-domesticated animals in North America."

white-nose syndrome map 2013

The spread of white-nose syndrome since 2006. Click map to enlarge. (Image: U.S. FWS)

Named for a telltale fuzz on the noses, ears and wings of infected bats, white-nose syndrome was initially a mystery to scientists, who spent years trying to figure out what it was. Rather than killing bats directly, it seems to prematurely wake them up from hibernation, causing them to fly outside in winter despite a scarcity of food. Its victims often have empty stomachs and low fat stores, suggesting they starved to death.

In 2011, scientists finally traced WNS to a novel fungus, Geomyces destructans, that's similar to a species from Europe. Since European bats seem immune, the leading theory is that humans accidentally carried fungal spores across the Atlantic, where American bats were blindsided. (Mammals' warmth usually thwarts cold-loving fungi, but hibernation opens a loophole by cooling down bats' bodies.) Much like Dutch elm disease or chestnut blight, the foreign fungus then ran amok, transmitted mainly among bats but also helped by human cavers who didn't wash spores off their shoes, clothes and equipment.

A swath of caves and other "hibernacula" have since been closed to the public as a precaution, and decontamination is now common at bat habitats still open to spelunking. But WNS has continued to invade caves even without tourists to let it in. The disease was recently discovered at Long Cave in Kentucky's Mammoth Cave National Park, for example, despite a ban on human visitors dating back more than 80 years. Nonetheless, Kath says Illinois won't take any chances with its newfound outbreak.

"The IDNR recognizes that continued cave closures will require patience from the caving community and other citizens," Kath said Thursday. "However, the observed devastation to bat populations and the evidence for human-assisted spread justifies that we exercise an abundance of caution in managing activities that impact caves and bats. We understand these measures will not be a cure for WNS, but they are necessary to help slow the spread of this affliction and to reduce the risks to surviving bat populations in North America."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

U.S. bat epidemic spreads to 20th state
White-nose syndrome has been confirmed in Illinois, state officials announced this week, marking the 20th state affected by the deadly, fast-moving bat disease.