What Causes Ebola?
An infection with the Ebola virus is what causes Ebola. Three of the four identified subtypes have caused disease in humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory Coast. The exact origin, locations, and natural habitat of the 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 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 among humans occurs through direct contact with infected people or their blood (or other body fluids).
(Click Causes of Ebola for more details about the Ebola virus and how it causes disease, including information about the incubation period.)