Questions & Answers
Japanese encephalitis - The Disease
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  1. What is Japanese encephalitis (JE)?

    A severe infection of the brain and spinal cord caused by the bite of a Culex mosquito carrying the JE virus. The disease is most common in rural, agricultural areas of east and southeast Asia (e.g., Okinawa, Burma, Cambodia, Laos, Thailand) where mosquito larvae inhabit flooded rice fields and marshes. These mosquitoes feed outdoors from dusk until dawn. Transmission is highest in summer and fall.

    Japanese encephalitis is not transmitted from person-to-person. It is the leading cause of viral encephalitis in Asia with 30,000 to 50,000 cases reported annually.

  2. Who is at risk for getting JE?
    Typically, residents of areas where JE is common, as well as travelers and deployed Service Members with extensive outdoor exposure in rural areas. Military personnel requiring immunization include: designated special-operation units; Navy mobile construction battalions; Marine expeditionary units operating in the Western Pacific; and troops assigned or deploying to Okinawa where extended field exposure is likely. For other travelers, immunize those who will spend one month or longer in rural areas, such as where rice cultivation or pig farming is common. Under normal circumstances, personnel stationed in Korea do not require immunization.


  1. What are the symptoms of JE?
    Most infections cause no symptoms. Mild infections cause a fever with headache. Severe infection develops rapidly, and causes severe headache, high fever, neck stiffness, disorientation, tremors, seizures (especially in infants), spastic paralysis and coma. Severe disease is deadly in 25% of infections.

  2. How is JE treated?
    Therapy for symptomatic Japanese encephalitis virus (JEV) infection is supportive. Patients often require feeding, airway management, and anticonvulsants for seizure control. No clearly effective antiviral agents exist.


  1. What are some specific complications of JE?
    About half of the people who survive serious JE infection are left with neurologic and psychological disabilities including behavior disorders, mental retardation, and seizures.