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- Japanese encephalitis virus (JEV): mosquito-borne flavivirus, similar to St. Louis encephalitis virus, Murray Valley encephalitis, yellow fever, dengue, and West Nile virus.
- Single-stranded, positive sense RNA virus.
- JEV is transmitted by Culex mosquitoes or species that lay eggs in flooded rice fields.
- Wild birds are natural host, and domestic pigs are amplifying host. Bats transmit disease in China.
- Blood transfusion and organ transplantation are potential modes of transmission.
- JEV is endemic in Asia, Southeast Asia, and the Pacific islands causing about 70,000 cases of infection and 14,000-20,000 deaths per year worldwide. 
- Map of JE transmission
- Risk of infection estimated at 1/5000 per month of travel to rural areas of Asia where transmission occurs.
- In temperate Asia, incidence of cases peaks in summer and fall.
- In tropics or subtropics, transmission occurs in wet seasons but may occur year-round.