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Japanese Encephalitis

Japanese Encephalitis (JE) virus is a single-stranded RNA virus that belongs to the Flavivirus genus, and is closely related to West Nile and St. Louis encephalitis viruses.

JE virus is the leading cause of vaccine-preventable encephalitis in Asia and the western Pacific. For most travelers to Asia, the risk for JE is very low but varies based on destination, duration of travel, season, and activities.  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, with an average incubation period of 5-15 days. 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.

There is no specific treatment for JE. Patient management focuses on supportive care and management of complications. Steps to prevent JE include using personal protective measures to prevent mosquito bites and vaccination.

Japanese Encephalitis Vero Cell vaccine (JE-VC) is an inactivated vaccine product, trade named IXIARO®. Currently, this is the only FDA-licensed vaccine for JE prevention available in the United States. IXIARO® is a sterile purified vero cell-culture-derived vaccine, available in single-dose, pre-filled syringes.

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 than1 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.

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Japanese Encephalitis and Japanese Encephalitis Vaccine

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