JAPANESE ENCEPHALITIS

What is it

Japanese encephalitis (JE) is a viral disease transmitted by mosquitoes that may cause inflammation of the membranes around the brain.1 JE virus is the most common vaccine-preventable cause of encephalitis in Asia.²

Japanese encephalitis occurs in almost all Asian countries and parts of the western Pacific.² It is mainly a threat in rural agricultural areas where there is widespread irrigation (artificial watering of crops).³

Who is at risk

Most travelers to countries where the disease is endemic are at very low risk for JE. However, some travelers are at increased risk for infection on the basis of their travel plans.²

Factors that increase the risk for JE virus exposure include:²

visit rural and agriculture areas, especially for an extended period of time (≥ 1 month) and during the JE virus transmission season
Do outdoor activities (e.g. hiking, camping, cycling, fieldwork) and staying in accommodations without air conditioning, screens, or bed nets.

What are the symptoms

Most infected people don’t develop any symptoms, but in those who do, the disease can be serious. Symptoms include the onset of high fever and headaches, which appear after five to fifteen days of incubation. Japanese encephalitis also affects the central nervous system, resulting in behavioral changes and movement disorders.⁴ Because unvaccinated travelers from nonendemic countries are usually immunologically naïve, travel-associated JE can occur in persons of any age.²

<1% of persons infected with JE virus develop encephalitis (brain swelling).²

How is it spread

Infected mosquitoes transmit JE virus to humans. The virus is not spread from person to person through direct contact.²

How is it prevented

Japanese encephalitis is a vaccine-preventable disease.² Consult a healthcare provider or visit a travel health clinic preferably 6 weeks before you travel.⁴

All travelers to countries where JE is endemic should be advised to take precautions to avoid mosquito bites to reduce the risk for JE and other diseases. For some persons who might be at increased risk for JE, the vaccine can further reduce the risk for infection.²

JE vaccine is recommended for persons:²

moving to a JE-endemic country to take up residence
longer-term (e.g., ≥1 month) travelers to JE-endemic areas
frequent travelers to JE-endemic areas

JE vaccine also should be considered for:²

for travelers to JE-endemic areas who are uncertain about their specific travel duration, destinations, or activities.

JE vaccine is not recommended for travelers with very low-risk itineraries, such as shorter-term travel limited to urban areas or outside of a well-defined JE virus transmission season.²

How is it treated

JE treatment consists of supportive care and management of complications. No antiviral agent or specific medication is available to mitigate the effects of JE virus infection.²

For further information regarding Japanese encephalitis and immunization, please speak with your healthcare provider.

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