Meaning : 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.