|Electron microscope image of the Ebola virus (source: CDC)|
The virus comes from the filoviridae family, similar to the Marburg virus. It is named after the Ebola River in Zaire, Africa, near where the first outbreak was noted by Dr. Ngoy Mushola in 1976 after a significant outbreak in Yambuku, Zaire (now the Democratic Republic of the Congo), and Nzara, in western Sudan. Of 602 identified cases, there were 397 deaths.
The two strains identified in 1976 were named Ebola-Zaire (EBO-Z) and Ebola-Sudan (EBO-S). The outbreak in Sudan showed a lower fatality rate -- 50% -- compared to the 90% mortality rate of the Zaire strain. In 1990, a second, similar virus was identified in Reston[?], Virginia amongst monkeys imported from the Philippines, and was named Ebola-Reston.
Further outbreaks have occurred in Zaire/Congo (1995 and 2003), Gabon (1994, 1995 and 1996), and in Uganda (2000). A new subtype was identified from a single human case in the Côte d'Ivoire in 1994, EBO-CI.
Of around 1500 identified Ebola cases, two-thirds of the patients have died. The animal (or other) reservoir which sustains the virus between outbreaks has not been identified.
Among humans, the virus is transmitted by direct contact with infected body fluids such as blood. The cause of the index case[?] is unknown.
The incubation period of Ebola haemorrhagic fever varies from two days to three weeks. Symptoms are variable too, but the onset is usually sudden and characterised by high fever, prostration[?], myalgia, arthralgia[?], abdominal pains[?] and headache. These symptoms progress to vomiting, diarrhea, oropharyngeal lesions[?], conjunctivitis, organ damage (notably the kidney and liver) by co-localized necrosis, proteinuria, and bleeding both internal and external, commonly through the gastrointestinal tract. Death or recovery to convalescence[?] occurs within six to ten days.
No specific treatment has been proven effective, and no vaccine exists.