Each virus usually is associated with a particular rodent host species in which it is maintained. Arenavirus infections are relatively common in humans in some areas of the world and can cause severe illnesses. The virus particles are spherical and have an average diameter of 110-130 nanometers. Viewed in cross-section, they show grainy particles that are ribosomes acquired from their host cells. 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 .
Image shows extracellular virus particles budding from the cell surface.
Click the image to see a high-resolution version. Go to high-resolution version . By the 1960s, several similar viruses had been discovered and they were classified into the new family Arenaviridae. Since Tacaribe virus was found in 1956, new arenaviruses have been discovered on the average of every one to three years. A number of arenaviruses cause hemorrhagic disease.