Frequently Asked Questions

What is Japanese encephalitis?

Japanese encephalitis (JE) is a potentially severe disease. JE is caused by a virus spread by infected mosquitoes in Asia and the western Pacific. JE virus is one of a group of mosquito-transmitted viruses that can cause inflammation of the brain (encephalitis).

Where does Japanese encephalitis occur?

JE occurs in Asia and parts of the western Pacific. It usually occurs in rural or agricultural areas, often associated with rice farming. In temperate areas of Asia, transmission is seasonal, and 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.

How soon do people get sick after being bitten by an infected mosquito?

It takes 5 to 15 days after the bite of an infected mosquito to develop symptoms.

 Top of Page

What are the symptoms of Japanese encephalitis?

Most people who are infected develop mild symptoms or no symptoms at all. In people who develop severe disease, initial symptoms include fever, chills, headache, fatigue, nausea and vomiting. The disease can progress to inflammation of the brain (encephalitis) and is often accompanied by seizures. Coma and paralysis occur in some cases.

 Top of Page

How is Japanese encephalitis diagnosed?

Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.

 Top of Page

What is the treatment for Japanese encephalitis?

There is no specific treatment. Severe illnesses are treated by supportive therapy which may include hospitalization, respiratory support, and intravenous fluids.

 Top of Page

What should I do if I think a family member might have Japanese encephalitis?

Consult a healthcare provider for evaluation and diagnosis.

 Top of Page

How can people reduce the chance of getting infected?

  • Use insect repellent and wear long pants and sleeves
  • Sleep in air-conditioned or well-screened rooms or use bed nets
  • A vaccine against JE virus is available. Talk to your healthcare provider about whether this vaccine is right for you.

 Top of Page

Who should get Japanese encephalitis vaccine?

JE vaccine is recommended for travelers who plan to spend at least 1 month in endemic areas during the JE virus transmission season. 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 exposure. Higher-risk activities include participating in extensive outdoor activities (such as camping, hiking, trekking, biking, fishing, hunting, or farming) and staying in accommodations without air conditioning, screens, or bed nets.
  • Travelers to an area with an ongoing outbreak.
  • Travelers to endemic areas who are uncertain of specific travel destinations, activities, or duration.

 Top of Page

How long does the Japanese encephalitis vaccination last?

The duration of protection is unknown. For persons aged 17 years and older, a booster dose may be given if the primary two-dose vaccination series was given one year or more previously and there is continued risk of exposure. Although studies are being conducted on the need for a booster dose for children, data are not yet available.

 Top of Page

What are the side effects of Japanese encephalitis vaccination?

Pain and tenderness are the most commonly reported symptoms. Headache, muscle pain and fatigue can also occur.

 Top of Page

I think I got sick from the vaccine, what should I do?

Consult with your healthcare provider. Ask your healthcare provider to report your case to the Vaccine Adverse Events Reporting System (VAERS)External if he or she thinks the vaccine has made you sick.

 Top of Page