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, 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 studying the immunology of bats might help in the development of treatments for AIDS.