Causes of Ebola
The Ebola virus is the primary cause of Ebola. There are four identified subtypes, and all but one are known to have caused disease in humans. There are no other known causes. Human-to-human transmission of the virus occurs through direct contact with infected people, or their body fluids (such as blood or secretions).
The Ebola virus got its name from a river in the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was first recognized. It is one of two members of a family of RNA viruses known as Filoviridae. There are four identified subtypes, three of which have caused disease in humans:
- Ebola-Ivory Coast.
The fourth Ebola virus subtype, Ebola-Reston, has caused disease in nonhuman primates, but not in humans.
The exact origin, locations, and natural habitat (known as the natural reservoir) of Ebola virus remain unknown; however, on the basis of available evidence and the nature of similar viruses, researchers believe that the Ebola virus lives in an animal host that is native to the African continent. They continue to search for the exact animal.
Just as scientists are unsure of the animal host for the Ebola virus, they are also unsure how an outbreak of Ebola virus occurs. Researchers have hypothesized that the first patient becomes infected through contact with an infected animal.
Once Ebola virus infects the first human, scientists do know how the virus is spread from human to human. Transmission occurs through direct contact with people who have Ebola or their body fluids (such as blood or secretions). The spread of Ebola most often occurs during the late stages of an infection.
When someone becomes infected with Ebola, he or she will not feel sick immediately. For 2 to 21 days, the person feels normal; however, inside his or her body, the virus is multiplying. This period between transmission of the virus and the beginning of Ebola symptoms is called the incubation period.