JEV is a virus from the family Flaviviridae part of the Japanese encephalitis serocomplex of 9 genetically and antigenically related viruses, some which are particularly severe in horses, and four known to infect humans including West Nile virus.
While most infections result in little or no symptoms, occasional inflammation of the brain occurs. In these cases, symptoms may include headache, vomiting, fever, confusion and seizures.
JEV is generally spread by mosquitoes, specifically those of the Culex type. Pigs and wild birds serve as a reservoir for the virus. The disease mostly occurs outside of cities.
The disease occurs in Southeast Asia and the Western Pacific.