WASHINGTON - In a government lab where scientists slice open dead animals to study the exotic diseases that killed them, Carol Meteyer peered through a microscope at hundreds of little bats and started to notice something very weird.

The bats had managed to survive the white-nose fungus that had killed millions of other bats hibernating in caves, mostly in the Northeast. But they had succumbed to something else that had left their tiny corpses in tatters, their wings scorched and pocked with holes.

Meteyer finally realized what had happened: In the struggle to fight off the fungus that causes white-nose syndrome, the bats were killed by their own hyperaggressive immune systems.

Meteyer, a scientist for the U.S. Geological Survey (USGS), had stumbled upon a phenomenon never before seen in mammals in the wild. A similar finding had been observed only once before - in people with AIDS.

Now scientists hope that studying the immunology of bats might help in the development of treatments for AIDS.

The devastating immune-system attack, called IRIS for immune reconstitution inflammatory syndrome, plays out differently in humans and bats, according to an article by Meteyer and two colleagues that recently appeared in the journal Virulence.

When bats hibernate in winter, their heart rates slow and their immune systems all but shut down, making them vulnerable to the cave-dwelling fungus Geomyces destructans that causes white-nose and eats away skin, connective tissue and muscle.

When bats wake up in late March, their immune systems react like startled homeowners who realize prowlers are inside the house. They launch a wild search-and-destroy mission that annihilates the disease, but also healthy cells and tissue.

For AIDS patients, the immune-system syndrome plays out differently. After antiretroviral treatment improves patients' health, their restored immune systems can launch an exaggerated attack against any previously acquired opportunistic infection the treatment didn't catch, causing extensive damage.

Scientists now hope to study the immunology of bats to try to uncover findings that can assist the development of treatments for AIDS.

Meteyer said she envisions a day when "we can look closely at the mechanism driving this intense response in bats and potentially get insight into this phenomenon in humans."

Her co-author, Judith Mandl, a research fellow for the National Institutes of Health involved in AIDS research, was also intrigued by the similarities between bat and human reactions. "When you release immune suppression, you get a response that's a lot more damaging than helpful," she said. The third co-author is Daniel Barber, who also works at NIH.

The remote possibility that an AIDS treatment can arise from the study of white-nose is about the only positive development since the bat disease was first discovered in a cave near Albany, N.Y., in 2008.

Between 5 million and 7 million bats of various species have died from the disease since that year. In Pennsylvania alone, 95 percent of little brown bats have died.

Bats have an ugly reputation as villains in books and movies, but in reality are as important as birds and bees. They pollinate plants, and a single reproductive female consumes her weight in bugs each night. A colony of 150 brown bats can eat enough adult cucumber beetles to prevent the laying of eggs that results in 33 million rootworm larvae in summer, according to a study cited by Bat Conservation International.

A 2009 study estimated that 1,320 metric tons of insect pests were not eaten because of the decline in bat numbers, requiring farmers to buy and apply more pesticides.

Meteyer started studying diseased bats in Madison when they first flew out of caves with white-nose and plopped into the yards of homeowners. Dead bats were boxed and shipped to the U.S. Fish and Wildlife Service for study.