The incubation period can last from two days to three weeks, and diagnosis is difficult. The human disease has so far been mostly limited to Africa, although one strain has cropped up in the Philippines.
Healthcare workers are at risk if they treat patients without taking the right precautions to avoid infection. People are infectious as long as their blood and secretions contain the virus - in some cases, up to seven weeks after they recover.
World Health Organization guidance on Ebola
Ebola crisis: Five ways to avoid the deadly virus
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Where does it strike?
Ebola outbreaks occur primarily in remote villages in Central and West Africa, near tropical rainforests, says the WHO.