Viral hemorrhagic fevers

History

Because these viruses are so diverse and occur in different endemic geographic locations, a comprehensive discussion is beyond the scope of this handbook. However, each viral infection possesses a number of different features that may provide insight into their possible importance as biological threat agents.

Arenaviridae: Lassa virus causes Lassa fever in West Africa, where endemic transmission is related to infected Mastomys rodents. Over 5,000 deaths in West Africa are attributed to Lassa each year, with between 200,000 - 300,000 annual infections. Argentine hemorrhagic fever (AHF) is caused by Junin virus and was first described in 1955 among field workers who harvested corn. From 300 to 600 cases per year occur in areas of the Argentine pampas. Bolivian, Brazilian, and Venezuelan hemorrhagic fevers are caused by the related Machupo, Guanarito, and Sabia viruses, respectively. Nosocomial transmission is probably possible with all Arenavirus infections but is frequently a problem with Lassa fever. Lassa infection of health-care workers has been attributed to parenteral exposures, contact with body fluids, and aerosols generated by patients. These viruses are transmitted from their rodent reservoirs to humans through inhalation of dusts contaminated with rodent excreta.

Bunyaviridae: Congo-Crimean hemorrhagic fever (CCHF) is a tick-borne disease with a widespread distribution from sub-Saharan Africa through southeastern Europe, Central Asia and the Indian sub-continent. It may also be spread by contact with the body fluids or slaughtered meat of infected animals and in health-care settings. Rift Valley fever (RVF) is a mosquito-borne disease that occurs in Central Africa. The hantaviruses are rodent-borne viruses with a wide geographic distribution. Hantaan and closely related Old World hantaviruses cause hemorrhagic fever with renal syndrome (HFRS). Hantaan virus infection is also known as Korean hemorrhagic fever or epidemic hemorrhagic fever. This is the most common human disease due to hantaviruses. It was described before WW II in Manchuria along the Amur River, among United Nations troops during the Korean conflict, and subsequently in Japan, China, and in the Russian Far East. Severe disease also occurs in some Balkan states, including Bosnia, Serbia, and Greece. Nephropathia epidemica is a milder disease that occurs in Scandinavia and other parts of Europe and is caused by a virus carried by bank voles (small rodents of the genus Microtus and related genera). New World hantaviruses cause hantavirus pulmonary syndrome (HPS) in the Americas. However, HPS generally does not present as a hemorrhagic fever. The hantaviruses are transmitted to humans via inhalation of dusts contaminated with rodent excreta.

Filoviridae: Ebola hemorrhagic fever was first recognized in the western equatorial province of the Sudan and a nearby region of Zaire in 1976. A second outbreak occurred in Sudan in 1979. In 1995 a single index case resulted in a large outbreak (316 cases) in Kikwit, Zaire. Subsequent epidemics have occurred in Gabon, Ivory Coast, Uganda, Republic of Congo, and Sudan. The Zaire and Sudan species of Ebola virus cause severe disease with high mortality. Reasearchers have been unable to identify a natural reservoir, and it is not known why this disease appears intermittently. A related virus (Ebola Reston) was isolated from monkeys imported into the United States from the Philippine Islands in 1989. Infected monkeys developed hemorrhagic fever. While subclinical infections 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 in Yugoslavia, among people exposed to African green monkeys. It resulted in 31 cases with seven deaths. Filoviruses may 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.

Flaviviridae: Yellow fever and dengue are two mosquito-borne diseases that have great importance in the history of military campaigns and military medicine. Tick-borne flaviruses include the agents of Kyasanur Forest disease in India, and Omsk hemorrhagic fever in Siberia.

All of the VHF agents (except for dengue virus) are laboratory infectious hazards by aerosol. The aerosol infectivity for many VHF agents has been studied and quantified in experimental animal models. VHF agents cause severe disease, and many have an extremely high rate of fatality. For these reasons, the VHF agents are considered a significant threat for BW use.

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