Researchers believe that the Ebola virus lives in an animal host that is native to the African continent, based on available evidence and the nature of similar viruses; however, the exact locations, origin, and natural habitat (known as the natural reservoir) of the virus remain unknown. 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 occurs. Researchers have hypothesized that contact with an infected animal is how the first patient with Ebola fever becomes infected with the virus.
Once the virus infects the first human, transmission of Ebola fever continues through direct contact with an infected person or his or her body fluids (such as blood or secretions). The late stages of an infection are typically when the spread of the virus occurs.
When a person becomes infected with Ebola virus, it begins to multiply within the body. Symptoms usually begin about four to six days after being infected. The period between infection with Ebola fever and the start of symptoms is called the incubation period. For Ebola fever, this can be as short as 2 days or as long as 21 days.
Ebola fever symptoms usually appear suddenly. They may include:
- Sore throat
- Severe headache
- Joint and muscle aches
- Dry, hacking cough
- Stomach pain
- External bleeding
- Internal bleeding.
(Click Ebola Symptoms for more information.)