Japanese encephalitis is a virus found mainly in India, China, Japan, and South East Asia. It is transmitted by certain mosquitoes, mainly Culex tritaeniorhynchus. This type of mosquito breeds in rice paddies and other standing water. Most cases of the diseases are found in Asian rural areas.
The majority of Japanese encephalitis cases are in children. People most at risk are foreigners living in rural areas, e.g., active duty military personnel living in affected areas, and residents of rural areas in affected locations. Travelers from the US to Asian countries usually are at very low risk. Globally approximately 35,000-50,000 symptomatic cases are reported per year.
Japanese encephalitis can be asymptomatic, mild, or severe. A mild infection would typically have only fever and a headache. A severe infection can cause swelling of the brain, high fever, neck stiffness, disorientation, seizures, stupor, paralysis, coma, and death.
A Japanese encephalitis vaccine is available but is not recommended for people who travel routinely to Asia for short visits. The vaccine is intended for people planning longer stays in endemic or epidemic areas. See the CDC Travel Vaccines page for more on travel vaccination.
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