Arenavirus is a genus of virus. The type species is Lymphocytic choriomeningitis virus (LCMV); it also includes the
species responsible for Lassa fever.

Whitewater Arroyo virus causes Hemorrhagic fever in the Southwest USA

Some arenaviruses are zoonotic pathogens and are generally associated with rodent-transmitted disease in humans.
Each virus usually is associated with a particular rodent host species in which it is maintained. The virus particles are
spherical and have an average diameter of 110-130 nanometers. All are enveloped in a lipid membrane. Viewed in
cross-section, they show grainy particles that are ribosomes acquired from their host cells. It is this characteristic that
gave them their name, derived from the Latin "arena," which means "sandy." Their genome, or genetic material, is
composed of RNA only, and while their replication strategy is not completely understood, we know that new viral
particles, called virions, are created by budding from the surface of their hosts’ cells.
http://encyclopedia.thefreedictionary.com/arenavirus