An arenavirus is any of a group of RNA virus of the genus Arenavirus, most of which cause severe diseases transmitted by rodents.
Lassa virus (LASV) causes Lassa fever. It's an arenavirus.
Junín virus an arenavirus http://en.wikipedia.org/wiki/Argentine_hemorrhagic_fever
Viruses of the Arenaviridae family cause the Argentinian, Brazilian, Bolivian, and Venezuelan hemorrhagic fevers. Lassa fever, which occurs in west Africa, also arises from an arenavirus.