Health officials believe that most cases of Ebola in West Africa are spreading person-to-person. But preventing future outbreaks may depend on finding the virus's source in nature, and that may have to wait until the current outbreak is tamed.
Ebola has caused two dozen outbreaks in Africa since 1976. Scientists think it may come from certain bats, but the link is not proved and many other animals are suspected of playing a role.
The current outbreak has killed more than 1,100 people in four countries, the worst toll from Ebola in history. Doctors think it started with a 2-year-old in Guinea in December, but they don't know how she was infected. Other evidence suggests Ebola may have been smoldering in the region for years undetected.