A New World arenavirus that cause a slow developing fever, malaise, headache, muscular pains, nausea, vomiting in the beginning stage. Later symptoms include petechiae or blood spots on the upper body, excessive nose, gum, stomach, and intestine bleeding when the disease progresses to the hemorrhagic phase.

The disease has an incubation period of 7-16 days and is limited to the area of Junin, 240 km west of Buenos Aires in Argentina where local rodent Calomys laucha and C. musculinus carry the virus and shows a very sharp seasonal pattern of occurrence between February and August. It is often spread among farmers who inhale virus secreted in urine or droppings as the soil is disturbed.

A safe and effective vaccine providing long-term protection (Candid-1) is available in Argentina and has the status of an investigational new drug in the United States. It also provides protection against Bolivian hemorrhagic fever.