Transmission is more frequent in rural areas, flooded rice paddies, and especially during rainy season. The risk to the average traveler is less than 1 per million per year.
Risk is increased by prolonged stays in endemic settings.
Etiology Japanese encephalitis is caused by a virus from the Flaviviridae family. Clinical Presentation Presenting symptoms are typical of encephalitis and include fever, lethargy, and altered mental status. The vaccine is made of inactivated virus and is given as a three-shot primary series given over 2 to 4 weeks. Serious allergic reactions including urticaria, angioedema, and anaphylaxis occur at the rate of about 15 to 62 per 10,000 doses. Serious allergic reactions may occur as long as 2 weeks after a dose is administered.