In people with AIDS, the immune system goes into overdrive after antiretroviral drugs suppress HIV infection and restore a person's health. The immune system then tries to fight off any other underlying infection. In bats, this happens after the animals wake from their winter torpor. During that stage, the immune system is suppressed, which allows the Geomyces destructans fungus to colonize the bats' skin in the first place. In both cases, the awakened immune system goes out of control and attacks healthy tissue as well as infected cells.