Japanese encephalitis is a mosquito-borne virus that leads to swelling of the brain. It can affect the central nervous system and cause severe complications, even death.


Japanese encephalitis can occur if you are bitten by a mosquito infected with the virus.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

The following factors increase your chance of being exposed to Japanese encephalitis. If you have any of these risk factors, tell your doctor:

  • Living or traveling in certain rural parts of Asia—According to the US Centers for Disease Control and Prevention, there have been outbreaks of Japanese encephalitis in China, Korea, Japan, Taiwan, and Thailand. These countries have controlled the disease through vaccinations. Other countries that still have periodic epidemics include Vietnam, Cambodia, Myanmar, India, Nepal, and Malaysia.
  • Being a laboratory worker who might be exposed to the virus


Symptoms of Japanese encephalitis usually appear 5-15 days after the bite from an infected mosquito. If you experience any of these symptoms, don’t assume it is because of Japanese encephalitis. These symptoms may be caused by other, less serious health conditions. If you experience any one of them, see your physician.

  • Agitation
  • Brain damage
  • Chills
  • Coma
  • Confusion
  • Convulsions (especially in infants)
  • Fever
  • Headache
  • Nausea
  • Neck stiffness
  • Paralysis
  • Tiredness
  • Tremors
  • Vomiting


Your doctor will ask about your symptoms and medical history, and perform a physical exam. Tests may include the following:

  • Blood tests to look for antibodies
  • CT scan —a type of x-ray that uses a computer to make pictures of structures inside the body
  • MRI scan —a test that uses magnetic waves to make pictures of structures inside the body
  • Cerebrospinal fluid tests


Since there is no specific treatment for Japanese encephalitis, care is concentrated on treating specific symptoms and complications.


There is a Japanese encephalitis vaccine which is recommended for people who live or travel in certain rural parts of Asia (see names of countries above ), and for laboratory workers who are at risk of exposure to the virus. Also, take the following measures to protect yourself from mosquito bites to prevent the disease:

  • Remain in well-screened areas.
  • Wear clothes that cover most of your body.
  • Use insect repellents that contain up to 30% NN-diethyl metatoluamide (DEET) on skin and clothing.