a large heterogeneous group of RNA viruses divisible into groups on the basis of the virions
they have been recovered from arthropods, bats, and rodents
most are borne by arthropods
they are linked by the epidemiologic concept of transmission between vertebrate hosts by arthropod vectors (mosquitoes, ticks, sandflies, midges, etc.) that feed on blood
they can cause mild fevers, hepatitis, hemorrhagic fever, and encephalitis