The Ebola outbreak in West Africa is the world's deadliest to date and the World Health Organization has declared an international health emergency as more than 1,200 people have died of the virus in Guinea, Liberia, Sierra Leone and Nigeria this year.
What is Ebola? Ebola is a viral illness of which the initial symptoms can include a sudden fever, intense weakness, muscle pain and a sore throat, according to the World Health Organization (WHO). And that is just the beginning: subsequent stages are vomiting, diarrhoea and - in some cases - both internal and external bleeding.
The disease infects humans through close contact with infected animals, including chimpanzees, fruit bats and forest antelope.
It then spreads between humans by direct contact with infected blood, bodily fluids or organs, or indirectly through contact with contaminated environments. Even funerals of Ebola victims can be a risk, if mourners have direct contact with the body of the deceased.
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
Where does it strike?
Ebola outbreaks occur primarily in remote villages in Central and West Africa, near tropical rainforests, says the WHO.
Bushmeat - from animals such as bats, antelopes, porcupines and monkeys - is a prized delicacy in much of West Africa but can also be a source of Ebola.
It was first discovered in the Democratic Republic of Congo in 1976 since when it has mostly affected countries further east, such as Uganda and Sudan. This outbreak is unusual because it started in Guinea, which has never before been affected, and is spreading to urban areas.
Source: The BBC.