ST. LOUIS (AP) — Officials with the U.S. Forest Service are cautiously optimistic that a new treatment may help bats survive a disease known as white-nose syndrome that has killed millions of bats.

About 60 brown bats found with the disease last fall but successfully treated were released back into the wild Tuesday at the Mark Twain Cave complex near the northeast Missouri town of Hannibal.

"While more research is needed before we know if our current discovery is an effective and environmentally safe treatment for white-nose syndrome, we are very encouraged," Michael T. Rains, director of the Forest Service's Northern Research Station and the Forest Products Laboratory, said in a statement.

National Wildlife Research Program Leader Monica Tomosy said at the bat release that white-nose syndrome is "among the most devastating wildlife diseases in recent memory," according to the Hannibal Courier-Post.

The syndrome is named for the white fungus that appears on the noses of bats. First detected in New York State in 2006, it has killed an estimated 5 million to 6 million bats in 28 states and Canada. It was first seen in Missouri about five years ago.

There is no known human health risk associated with white-nose syndrome.

The Forest Service said the syndrome is caused by a cold-loving fungus, pseudogymnoascus destructans, or Pd, which penetrates tissues of the nose, mouth and winds, compromising the bats' ability to avoid dehydration and maintain body temperature.

The Forest Service worked with universities and state wildlife agencies, using funding from Bat Conservation International and The Nature Conservancy, on the treatment project.

Forest Service wildlife biologist Sybill Amelon and fungal disease specialist Daniel Lindner, and Georgia State University scientist Chris Cornelison, believe native soil bacteria produce natural volatiles that inhibit growth of the fungus. Their field trials treated diseased bats in labs with compounds produced by the bacteria.

The health of many of those bats improved markedly, according to the Forest Service, including the bats released near Hannibal.

Bats play a major role in the ecosystem, serving as a major predator for insects that can damage forests and crops. The Forest Service said bats have an estimated value of $23 billion annually to the agricultural industry.