This undated photo courtesy of the U.S. Fish & Wildlife Service shows a biologist holding a gray bat. (AFP/GETTY IMAGES)

The deadly white-nose disease has been detected in endangered gray bats, federal wildlife officials announced Tuesday, raising a very real possibility that the species could be wiped out within two years.

White-nose syndrome has killed millions of other species of bats as they hibernated in caves and mines in the northeastern United States, but the gray bat is even more susceptible, the U.S. Fish and Wildlife Service said.

Gray bats so far are the only infected species that live year-round in caves, giving the plague an opportunity to kill them more efficiently and in larger numbers, biologists said. Ninety percent of gray bats gather in nine caves in five states, in colonies as large as 1 million and no smaller than 200,000.

“They could potentially be wiped out in just a couple of years,” said Ann Froschauer, the Fish and Wildlife Service’s national communications leader on white-nose syndrome. “If the disease behaves in a similar way it has in the Northeast, we really could be looking at losing this species.”

The bats’ value to farmers is enormous, said Paul McKenzie, the endangered species coordinator for Fish and Wildlife in Missouri. In that state alone, gray bats eat about 223 billion insects a year, 490 metric tons, according to a study by the state Department of Conservation. A colony of 250,000 can eat a ton of flies, beetles, moths and other farm pests per night. Biologists think there are 3.5 million to 4.5 million gray bats in mostly five states.

“The economic impact to our economy could be huge if we lose gray bats. If we don’t have gray bats consuming these insects . . . what a farmer needs is more pesticides . . . so you add that to the environment,” McKenzie said. “The fact that gray bats are now being impacted by white-nose syndrome is pretty devastating.”

Before white-nose was detected in the South for the first time in March, Fish and Wildlife officials had discussed removing the gray bats from the endangered list. The bats were listed in the 1970s, when human development encroached on their habitat, lowering their numbers.

“This was an endangered species that was well on its way to recovery,” McKenzie said. Now “it just remains to be seen.”

An estimated 6.7 million bats have died in 12 states and four Canadian provinces since white-nose syndrome was first detected at Howes Cave near Albany, N.Y., in 2006. The little brown bat and Indiana bats have suffered 90 percent declines in the Northeast.

Virginia’s big-eared bats, on the other hand, have thrived so far, despite the disease’s presence in their caves, and that experience offers some hope for the gray bat, McKenzie said.

The disease is caused by an aggressive fungus called Geomyces destructans that eats through the skin and membranes of bats. A gray bat tested positive for the fungus, but not the disease, two years ago.

A gray bat was sent to a lab for testing in February, and a positive result was confirmed in April. A second confirmation was made in May by the National Wildlife Health Center in Madison, Wis.

The Fern Cave National Wildlife Refuge in western Alabama has the largest documented wintering colony of gray bats, more than a million.

“It could spread exponentially through the cave. It could affect other species of bats. We just don’t know,” McKenzie said.