Bats in the northeastern United States are now emerging from their winter hibernation. But many thousands of them will be too weak to survive. A mysterious affliction called white-nose syndrome has been killing hundreds of thousands of the mammals in caves from New Hampshire to West Virginia. Evidence is building that the symptoms are caused by a new infectious disease that is skipping from cave to cave. As biologists race to find answers, the U.S. Fish and Wildlife Service is taking measures to check the syndrome's spread. In late March, the government agency recommended that people in states with white-nose syndrome stop exploring caves to avoid inadvertently transmitting the leading suspect in this deadly scenario: a new species of fungus.