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Japanese encephalitis

Published on May 10, 2024 at 8:00 / Updated on May 25, 2024 at 8:00

Japanese encephalitis is a potentially serious brain infection. It is caused by a virus found in Asian countries, primarily in Southeast Asia and Western Pacific regions.


The Japanese encephalitis virus is transmitted through the bite of an infected mosquito. The virus cannot be transmitted from one infected person to another. Mosquitoes carrying the Japanese encephalitis virus usually bite between sunset and sunrise. The risk of infection is highest in rural areas. Very few infections occur in large cities.

The infection period is limited to the warm season in countries or areas with a temperate climate, such as China, Japan, Korea, and Australia.

The infection can be transmitted year-round in Asian countries with a tropical climate, such as Burma, Brunei, Cambodia, Indonesia, Laos, Malaysia, the Philippines, Singapore, Thailand, East Timor, and Vietnam. The risk of infection is highest during the rainy season.


Most of the time, contracting the virus that causes Japanese encephalitis causes no or very few symptoms. Symptoms appear 5 to 15 days after the infection is transmitted via mosquito bite. The infected person may experience a mild headache and fever. In rare cases, they may have a severe attack, at which time they may present the following symptoms:

  • High fever
  • Intense headaches
  • Vomiting
  • Stiff neck
  • Disorientation
  • Seizures
  • Coma

The severe form of the disease is associated with a high fatality rate. Among those who survive, a certain number suffer sequelae such as recurrent seizures, paralysis, or the inability to speak.


Preventing Japanese encephalitis consists in avoiding mosquito bites. The following precautions will help limit the risk of getting bitten:

  • Use an effective mosquito repellent when doing outdoor activities
  • Spray your clothing and equipment with an insecticide (e.g.,  permethrin)
  • Wear clothing that covers your arms and legs
  • Keep doors and windows closed
  • Use mosquito netting

Individuals who are at higher risk of contracting this infection while travelling can be given a series of preventive vaccinations prior to departure. These vaccines must be scheduled a few weeks before departure because several doses are required. A person's risk level depends on their trip itinerary and duration. Ask your health care provider if the Japanese encephalitis vaccine is right for you.


There is no specific treatment for Japanese encephalitis. Some treatments may be administered to alleviate symptoms (e.g., pain medication for headaches).

When should I see a health care professional?

Promptly consult a health care professional if you experience the following symptoms while travelling:

  • Sudden onset of high fever with severe headaches
  • Seizures
  • Confusion and disorientation

If you get sick after you return from a trip or if you were sick while you were away, see a healthcare provider upon your return. Medical attention may be required.

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