WHEN AN EPIDEMIC strikes, the leaders of the attack against it are likely to be infectious disease experts from national or international organizations such as the CDC and the WHO. These highly trained men and women risk their lives to track and control epidemics, whether they are in Africa nursing a patient with Ebola or working in a protective "blue suit" in a high-tech laboratory filled with vials of deadly viruses. "We have to be prepared to do anything—clean floors, take samples [of blood and other body fluids], care for patients," says the CDC's Pierre Rollin, who went to Zaire when Ebola broke out there in 1995. "Conditions are very hard in the field . . . [sometimes including] no running water, no electricity, no clean needles. If you get into trouble, you cannot dial 911."

CDC to the rescue

In the United...