An infection with the Ebola virus is what causes Ebola. Three of the four identified subtypes of the Ebola virus have caused Ebola in humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory Coast. The exact origin, locations, and natural habitat of the Ebola virus remain unknown; however, researchers believe that the virus lives in an animal host in Africa.
It is not known exactly how an outbreak of Ebola virus occurs. Researchers theorize that the first person to develop Ebola in an outbreak becomes infected with the virus through contact with an infected animal. Transmission of Ebola among humans occurs through direct contact with people who have Ebola or their blood (or other body fluids).
(Click Causes of Ebola for more details about the Ebola virus and how it causes Ebola, including information about the incubation period for the virus.)
