Ebola Hemorrhagic Fever

Ebola hemorrhagic fever was first recognized in the western equatorial province of the Sudan and the nearby region of Zaire in 1976. A second outbreak occurred in Sudan in 1979, and in 1995 a large outbreak (316 cases) developed in Kikwit, Zaire, from a single index case. Subsequent epidemics have occurred in Gabon and the Ivory Coast. The African strains cause severe disease and death. It is not known why this disease appears infrequently.

Ebola Reston is a related virus that was isolated from monkeys imported into the United States from the Philippines in 1989, and which subsequently developed hemorrhagic fever. While infections have occurred among exposed animal handlers, Ebola Reston has not been identified as a human pathogen.

Marburg epidemics have occurred on six occasions: five times in Africa, and once in Europe. The first recognized outbreak occurred in Marburg, Germany, and Yugoslavia, among people exposed to African green monkeys, and resulted in 31 cases and 7 deaths.

Filoviruses can be spread from human to human by direct contact with infected blood, secretions, organs, or semen. Ebola Reston apparently spread from monkey to monkey, and from monkeys to humans by the respiratory route. The natural cause of the filoviruses is unknown.

Lassa virus causes disease in West Africa. These viruses are transmitted from rodents to humans by the inhalation of dusts contaminated with rodent excreta.

Yellow fever and dengue are two mosquito-borne fevers that have greatly affected human populations. Tick-borne filoviruses include the agents of Kyanasur Forest disease in India, and Omsk hemorrhagic fever in Siberia.

All of the viral hemorrhagic fevers, VHF agents, (except for dengue virus) are airborne infections in laboratory tests. In view of their airborne infectivity (and, for some viruses, high lethality), these viruses conceivably could be used as biological warfare agents.