Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) is a member of the genus Flavivirus, family Flaviviridae. It causes a rural, mosquito-borne, zoonotic viral disease that is a major public health problem in many Asian countries. The natural cycle involves rice-field breeding mosquitoes and domestic pigs or wading ardeids (e.g., egrets and herons). The most important vector is Culex tritaeniorhynchus, which is found in most parts of Asia and breeds in water pools and flooded rice fields. Humans and most other vertebrates are ‘dead-end’ hosts, producing low viremias, such that mosquitoes cannot be infected while feeding on them. Japanese encephalitis (JE) is characterized by infection of the central nervous system. It is the most important arthropod-borne virus encephalitis. At least 50 000 clinical cases of JE are reported each year. The case–fatality rate is approximately 25% and up to 70% of those who survive infection develop neurological sequelae. JE is the most important veterinary flavivirus disease. In addition to wild boars, two animal hosts are considered to be important: horses and pigs. Horses become encephalitic and are considered to be dead-end hosts, whereas JEV induces abortion in pigs, considered to be a major peridomestic amplifying host.