WHO has published Ebola virus disease: background and summary. Excerpt:
WHO is supporting the national authorities in the response to an outbreak of Ebola virus disease (EVD; formerly known as Ebola haemorrhagic fever). The outbreak is now confirmed to be caused by a strain of ebolavirus with very close homology (98%) to the Zaire ebolavirus. This is the first time the disease has been detected in West Africa. Cases were first reported from forested areas in south-eastern Guinea.
The outbreak has rapidly evolved and several districts and Conakry have reported cases and deaths caused by EVD. A small number of suspected cases and deaths has also been reported from neighbouring countries with all of them having crossed from Guinea. Confirmed cases have been reported from Guinea and Liberia.
Genus Ebolavirus is one of three members of the Filoviridae family (filovirus), along with genus Marburgvirus and genus Cuevavirus. Genus Ebolavirus comprises five distinct species: Bundibugyo ebolavirus (BDBV); Zaire ebolavirus (EBOV); Reston ebolavirus (RESTV); Sudan ebolavirus (SUDV); and Taï Forest ebolavirus (TAFV). BDBV, EBOV, and SUDV have been associated with large EVD outbreaks in Africa, whereas RESTV and TAFV have not. Samples taken from patients in this outbreak have tested positive for EBOV.
In Africa, fruit bats are believed to be the natural hosts of Ebola virus. The virus is transmitted from wildlife to people through contact with infected fruit bats, or through intermediate hosts, such as monkeys, apes, or pigs that have themselves become infected through contact with bat saliva or faeces.
People may then become infected through contact with infected animals, either in the process of slaughtering or through consumption of blood, milk, or raw or undercooked meat.
The virus is then passed from person to person through direct contact with the blood, secretions or other bodily fluids of infected persons, or from contact with contaminated needles or other equipment in the environment.
EVD, which has a case fatality rate of up to 90%, is a severe acute viral illness often characterized by the sudden onset of fever, intense weakness, muscle pain, headache, nausea and sore throat. This is followed by vomiting, diarrhoea, impaired kidney and liver function, and in some cases, both internal and external bleeding. Laboratory findings frequently include low white blood cell and platelet counts and elevated liver enzymes.
The incubation period, the time interval from infection with the virus to onset of symptoms, is 2 to 21 days. People remain infectious as long as their blood and secretions contain the virus, a period that has been reported to be as long as 61 days after onset of illness.