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

These risk factors increase your chance of developing Japanese encephalitis. Tell your doctor if you have any of these risk factors:

  • Living or traveling in certain rural parts of Asia—According to the US Centers for Disease Control and Prevention (CDC), 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. The CDC's Traveler's Health website provides the latest information for international travelers.
  • Being a lab 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, do not assume it is due to Japanese encephalitis. These symptoms may be caused by other conditions. Tell your doctor if you have any of these:

  • 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 do 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 focused on treating specific symptoms and complications.


There is a Japanese encephalitis vaccine. It is recommended for people who live or travel in certain parts of Asia and for lab workers who are at risk of exposure to the virus.

Also, take the following measures to protect yourself from mosquito bites:

  • Remain in well-screened areas.
  • Wear clothes that cover most of your body.
  • Use insect repellents that contain up to 30% NN-diethyl-meta-toluamide (DEET) on skin and clothing.
  • Use proper mosquito netting at night. Look for netting treated with insecticide.