One of the most frightening viruses to come out of the African subcontinent, the Ebola virus first appeared in 1976. More than 400 people in the Democratic Republic of Congo (formerly known as Zaire) and the neighboring Sudan were killed by the hemorrhagic fever that it caused. Ebola virus has been responsible for several outbreaks in the intervening years, including one in Zaire in the summer of 1995.

An unclassified ribonucleic acid (RNA) virus, Ebola is morphologically similar to Marburg virus. Both can cause headache, malaise, myalgia, and high fever, progressing to severe diarrhea, vomiting, and internal and external hemorrhage.

Four strains of the Ebola virus are known to exist: Ebola Zaire, Ebola Sudan, Ebola Tai, and Ebola Reston. All four types are structurally similar, although they have different antigenic properties. However, Ebola Reston causes illness only in monkeys, whereas the other three forms cause disease in humans.

The prognosis for Ebola virus infection is extremely poor, with mortality as high as 90%. The incubation period ranges from 2 to 21 days.