Argentine haemorrhagic fever (AHF) was first recognized in 1955 on the central pampas of Argentina, where before the deployment of a new vaccine in 1992, hundreds of cases occurred each year. It is caused by the Junín virus, which is carried by the corn mouse Calomys musculinus.
In 1955, the AHF-endemic area included approximately 10,000 km2 centred around the town of Junín in Buenos Aires province. By 1985, the AHF-endemic area encompassed more than 150,000 km2 in four provinces.