The Junin virus genome comprises two single stranded RNA molecules, each encoding two different genes in an ambisense orientation. The two segments are termed 'short (S)' and 'long (L)' due to their respective lengths. The short segment (around 3400 nucleotides in length) encodes the nucleocapsid protein and the glycoprotein precursor (GPC). The GPC is subsequently cleaved to form two viral glycoproteins, GP1 and GP2 which ultimately form the T-shaped glycoprotein spike which extends from the viral envelope. The long segment (around 7200 nucleotides in length) encodes the viral polymerase and a zinc binding protein.
Since the discovery of the Junin virus in 1958, the geographical distribution of the pathogen, although still confined to Argentina, has risen. At the time of discovery, Junin virus was confined to an area of around 15,000 km². At the beginning of 2000, the distribution had risen to around 150,000km². The natural hosts of Junin virus are rodents, particularly Mus musculus, Calomys spp. and Akodon azarae. Direct rodent to human transmission only transpires when contact is made with excrement of an infected rodent. This commonly occurs via ingestion of contaminated food or water, inhalation of particles within urine or via direct contact of broken skin with rodent excrement.