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Vector-borne diseases

Japanese encephalitis

Japanese encephalitis virus is transmitted to humans through infected Culex mosquitoes.

Japanese encephalitis causes an estimated 50 000 cases and 10 000 deaths every year, mostly of children aged less than 5.

It occurs across Asia, from the islands of the Western Pacific in the east to the Pakistani border in the west, and from Korea in the north to Papua New Guinea in the south.

Most human infections are asymptomatic or result in only mild symptoms. However, a small percentage of infected people develop inflammation of the brain (encephalitis), with symptoms including the sudden onset of headache, high fever, disorientation, coma, tremors and convulsions. One quarter of severe cases can be fatal, and 30% of those who survive severe infection have lasting central nervous system damage.

Transmission of the Japanese encephalitis virus occurs primarily in rural agricultural areas, particularly around flooded rice fields, but can also occur near urban centres. In temperate areas of Asia, transmission of the virus is seasonal.

The virus is transmitted between mosquitoes, in particular Culex tritaeniorhynchus, and animals such as pigs and wading birds. Humans are incidental or “dead-end” hosts, because they usually do not develop high-enough concentrations of the virus in their bloodstreams to infect feeding mosquitoes.

There is no specific treatment for the disease; supportive care and management of complications can provide some relief.

The vaccine against Japanese encephalitis is the single most effective preventive measure against this disease.