Japanese encephalitis, is virus infection of the brain that occurs most often in summer epidemics. Mortality is high (50-60%) but recovery, when it does occur, is rapid (10-14 days) and ordinarily complete. It is spread by mosquitoes from infected animals (usually pigs and wading birds) to humans.
In its early stages, Japanese encephalitis appears to be a flu-like illness with headache, fever, gastrointestinal symptoms, confusion and other behavior disturbances. In about one of every 200 cases, the illness progresses to inflammation of the brain, with more than half of those cases ending in permanent disability or death. There is currently no effective drug treatment for the disease once it sets in - it can only run its course. Infection during the first and second trimesters is associated with intrauterine infection and miscarriage.
Japanese encephalitis is a public health problem of increasing concern to countries of Southeast Asia and the western Pacific. Thousands of cases are occurring annually, with high case-fatality rates. The disease is expanding into new areas. Since the mosquito that carries the virus breeds in flooded rice fields and pools of water, most human infections occur in rural, agricultural areas (although occasional cases have been reported from urban locations). About 50,000 cases are reported each year among local populations.