EMERGING DISEASES MAY be frightening, but many experts think that the worst risk of devastating new epidemics comes instead from ancient illnesses, once thought to be defeated, that are now returning. "We have untreatable infections in our hospitals here in the U.S. right now," said Mitchell Cohen of the CDC's National Center for Infectious Diseases in 1996. "We know another flu pandemic is coming. To me, these things are of much more concern than something terrible from the jungle."

Plague: panic in India

One killer that staged a comeback during the 1990s was the most feared infectious disease of all: the plague. An epidemic of pneumonic plague, the most dangerous form of the disease, appeared in Surat, a city of about 2 million people on India's west coast, in September 1994. Some epidemiologists think the epidemic started because of an increase in...