A family of at least 13 RNA viruses, many of which are natural parasites of rodents, that includes lymphocytic choriomeningitis virus, Lassa virus, and the Tacaribe virus complex. The virions are 50 to 300 nm (average 100 nm) in diameter, enveloped, ether-sensitive, and contain single-stranded, segmented RNA (molecular weight 3 to 5 × 106); they also contain electron-dense, RNA-containing granules (20 to 30 nm in diameter) that resemble ribosomes, with an electron-microscopic appearance of sandiness.