Japanese Encephalitis (JE)

Clinical Description

Japanese encephalitis (JE) virus is the leading cause of vaccine-preventable encephalitis in Asia and the western Pacific.  Transmission of the JE virus is maintained in a cycle involving mosquitoes and vertebrate hosts, mainly pigs and wading birds. Humans can be infected when bitten by an infected mosquito. Most human infections are asymptomatic or result in only mild symptoms. However, a small percentage of infected persons develop inflammation of the brain (encephalitis), with symptoms including sudden onset of headache, high fever, disorientation, coma, tremors and convulsions. About 1 in 4 cases are fatal.

Source: http://www.cdc.gov/japaneseencephalitis/index.html


Japanese encephalitis (JE) should be considered in a patient with evidence of a neurologic infection (e.g., meningitis, encephalitis, or acute flaccid paralysis) who has recently traveled to or resided in an endemic country in Asia or the western Pacific.

Laboratory diagnosis of JE is generally accomplished by testing of serum or cerebrospinal fluid (CSF) to detect virus-specific IgM antibodies. JE virus IgM antibodies are usually detectable 3 to 8 days after onset of illness and persist for 30 to 90 days, but longer persistence has been documented. Therefore, positive IgM antibodies occasionally may reflect a past infection or vaccination. Serum collected within 10 days of illness onset may not have detectable IgM, and the test should be repeated on a convalescent sample. For patients with JE virus IgM antibodies, confirmatory neutralizing antibody testing should be performed. In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry, and virus culture of autopsy tissues can also be useful.

Diagnostic testing for JE virus IgM antibodies is commercially-available. Confirmatory testing is only available at CDC and a few specialized reference laboratories.

Source: http://www.cdc.gov/japaneseencephalitis/healthCareProviders/healthCareProviders-Diagnostic.html


Japanese encephalitis (JE) virus, a flavivirus, is closely related to West Nile and St. Louis encephalitis viruses. JE virus is transmitted to humans through the bite of infected Culex species mosquitoes, particularly Culex tritaeniorhynchus.

The virus is maintained in a cycle between mosquitoes and vertebrate hosts, primarily pigs and wading birds. Humans are incidental or dead-end hosts, because they usually do not develop high enough concentrations of JE virus in their bloodstreams to infect feeding mosquitoes.

JE virus transmission occurs primarily in rural agricultural areas, often associated with rice production and flooding irrigation. In some areas of Asia, these conditions can occur near urban centers.

In temperate areas of Asia, JE virus transmission is seasonal. Human disease usually peaks in the summer and fall. In the subtropics and tropics, transmission can occur year-round, often with a peak during the rainy season.

Source: http://www.cdc.gov/japaneseencephalitis/transmission/index.html


All travelers to Japanese encephalitis (JE) endemic areas should take precautions to avoid mosquito bites to reduce the risk for JE and other vector-borne infectious dis­eases. For some travelers who will be in a high-risk setting based on season, location, duration, and activities, JE vaccine can further reduce the risk for infection.

Avoid Mosquito Bites

  • Use Insect Repellent. When you go outdoors, use an EPA-registered insect repellent such as those containing DEET, IR3535, picaridin or oil of lemon eucalyptus. Even a short time outdoors can be long enough to get a mosquito bite. For more information about insect repellents, see Protection against Mosquitoes, Ticks, & Other Insects & Arthropods.
  • Wear Proper Clothing to Reduce Mosquito Bites. When weather permits, wear long-sleeves, long pants and socks when outdoors. Mosquitoes may bite through thin clothing, so treating clothes with repellent containing permethrin or another EPA-registered repellent will give extra protection. Don't apply repellents containing permethrin directly to skin.
  • Reduce Exposure to Mosquitoes During Peak Biting Hours. The mosquitoes that transmit JE virus feed mainly outside during the cooler hours from dusk to dawn. Travelers to high risk areas should consider minimizing outdoor activities at these times if possible. To reduce the risk of JE and other vector-borne diseases, travelers should stay in air-conditioned or well-screened rooms, or use a bed net and aerosol room insecticides.

Obtain Vaccine if Recommended

JE vaccine is recommended for travelers who plan to spend 1 month or more in endemic areas during the JE virus transmission season. This includes long-term travelers, recurrent travelers, or expatriates who will be based in urban areas but are likely to visit endemic rural or agricultural areas during a high-risk period of JE virus transmission.

Vaccine should also be considered for the following:

  • Short-term (less than 1 month) travelers to endemic areas during the transmission season, if they plan to travel outside an urban area and their activities will increase the risk of JE virus exposure. Examples of higher-risk activities or itineraries include: 1) spending substantial time outdoors in rural or agricultural areas, especially during the evening or night; 2) participating in extensive outdoor activities (such as camping, hiking, trekking, biking, fishing, hunting, or farming); and 3) staying in accommodations without air conditioning, screens, or bed nets.
  • Travelers to an area with an ongoing JE outbreak.
  • Travelers to endemic areas who are uncertain of specific destinations, activities, or duration of travel.
  • JE vaccine is not recommended for short-term travelers whose visits will be restricted to urban areas or times outside a well-defined JE virus transmission season.
  • More information about JE vaccine can be found here.

Source: http://www.cdc.gov/japaneseencephalitis/prevention/index.html


Available Vaccines

WHO-Prequalified Japanese Encephalitis Vaccines


Common Disease Taxonomy: