The genomic single stranded RNA of arenaviruses is multipartite, consisting of two segments, L (large, 7.2 kb) and S (small, 3.4 kb). Each segment forms a circle by hydrogen bonding of its ends. The RNA is negative sense, thus the naked genome is noninfectious. A unique property of the arenavirus genome is its ambisense capability (see link: "The Unique Property of Ambisense"). The RNA is neither capped or polyadenylated, and is contained in a helical nucleocapsid.

Among animal viruses, all helical nucleocapsids are enveloped, including those of arenaviridae. Arenavirus enveloped particles vary in diameter from 60 to more than 300 nm, with an average size of about 92 nm. The arenaviridae family takes its name from the Latin word for sand, arenosus, due to the sandy appearance of riboprotein structures within the virion. These ribosome-like structures are acquired from the host during the budding process, but their function is not yet understood.

Arenaviruses readily infect mammals. They can cause chronic infections in rodents indigenous to Europe, Africa, and the Americas. Rodents are often the laboratory host chosen for isolation of these viruses, and in fact, EVERY KNOWN RESERVOIR OF AN ARENAVIRUS IS A RODENT! LCMV has been reportedly isolated from mosquitos, but there is no indication that an arthropod host may be relevant to the life cycle of arenaviruses in nature. Asymptomatically infected rodents can move from their own habitat to invade human habitation. When humans come into contact with excreted virus, severe infection can result. Even nonhuman primates may suffer serious or fatal consequences of infection with arenaviruses which are known human pathogens.

The epidemiology of arenavirus diseases depends on patterns of infection in reservoir hosts and on the factors which bring man into contact with rodents or their saliva and urine. Humans are primarily infected with Lassa virus, for example, by eating infected rats or by eating food contaminated with rat excretions. Person to person transmission of Lassa only can occur mainly via direct contact, such as contamination of skin breaks with infected blood, or aerosol spread.

REFERENCES:
Fields, Virology, 1996. pgs. 1521-1535.
Siegel, Robert. The Humans and Viruses Course Reader. 1998. Lecture 10.
White and Fenner, Medical Virology, San Diego: Academic Press, 1994. pgs. 500-507.