Arenaviruses are enveloped viruses (about 120 nm diameter) with a bi-segmented negative strand RNA genome. The typical image in electronic microscopy showing grainy ribosomal particles (“arena” in latin) inside the virions gave the name to this family of viruses.
In 1933, the first virus of the Arenaviridae family, the Lymphocytic Choriomeningitis (LCM) virus, was isolated in North America from a human with aseptic meningitis. Other viruses causing hemorrhagic fevers were reported in South America: Machupo in 1956 in the Beni province of Bolivia, Junín in north Argentina, Guanarito in Portuguesa state in Venezuela in 1989, Sabia in Brazil in 1990 and more recently Chapare in 2004 in Bolivia. Lassa fever was identified in Nigeria in 1969.