Japanese Encephalitis


Japanese encephalitis is an infection from a mosquito. Rarely, it can affect the brain and nervous system. When this happens, it can be serious and even life-threatening.


Japanese encephalitis is caused by a virus. It is spread to humans from the bite of an infected mosquito. The virus is not spread from person to person.

Risk Factors

The risk of Japanese encephalitis is highest in areas that have outbreaks. Outbreaks have happened in rural parts of China, Korea, Japan, Taiwan, and Thailand. These countries now control the disease with vaccinations.

Countries that still have outbreaks are:

  • Vietnam, Cambodia, and Myanmar
  • Malaysia, India, and Nepal.

Lab workers exposed to the virus also have some risk.


Most people infected with Japanese encephalitis do not have symptoms. If symptoms happen, they can range from mild to severe.

Symptoms may be:

  • Fever and chills
  • Headache or neck stiffness
  • Nausea or vomiting
  • Confusion
  • Uncontrolled body movements
  • Not being able to move
  • Lack of responsiveness or coma


The doctor will ask about your symptoms and health history. A physical exam will be done.

Tests may be done to diagnose the infection. They may be:

Imaging tests may be done to check the brain. They may include:


There is no specific treatment for Japanese encephalitis. Treatment depends on how severe the disease is. The goal is to manage symptoms and problems. Hospital care may be needed.

Depending on the symptoms, options may be:

  • Pain medicines—for headaches
  • Anti-nausea medicines
  • Fluids—by mouth or IV
  • Breathing support


The risk of Japanese encephalitis may be reduced by:

  • A vaccine, which may be given to those who:
    • Live or travel to certain parts of Asia
    • Are lab workers at risk for exposure to the virus

The risk may also be reduced by:

  • Avoiding mosquito bites by:
    • Covering up the skin
    • Using bug sprays, netting, and screens
    • Staying inside between dusk and dark


Centers for Disease Control and Prevention
Infectious Diseases Society of America



Japanese encephalitis. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/japaneseencephalitis. Accessed April 5, 2021.
Japanese encephalitis VIS. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/vaccines/hcp/vis/vis-statements/je-ixiaro.html. Accessed April 5, 2021.
Japanese encephalitis virus vaccine, inactivated. EBSCO DynaMed website. Available at: https://www.dynamed.com/drug-monograph/japanese-encephalitis-virus-vaccine-inactivated. Accessed April 5, 2021.
Keng LT, Chang LY. Japanese encephalitis. CMAJ. 2018;190(21):E657
Mosquito avoidance. EBSCO DynaMed website. Available at:https://www.dynamed.com/prevention/mosquito-avoidance. Accessed April 5, 2021.
Last reviewed December 2020 by EBSCO Medical Review Board David L. Horn, MD, FACP
Last Updated: 4/5/2021

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