The member of the genus Flavivirus family Flaviviridae are arthropod-transmitted viruses. This genus includes vector-borne neurotropic viruses such as the tick-borne encephalitis virus serocomplex and the Japanese encephalitis virus serocomplex. Flavivirus encephalitis is the generic term for encephalitis caused by viruses belonging to this genus. The Japanese encephalitis virus is still active in Japan, and the tick-borne encephalitis virus is prevalent in Hokkaido, the northern region of Japan. The West Nile fever/encephalitis epidemic has been active in North and South America since 1999.