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Japanese Encephalitis

Japanese Encephalitis
Japanese Encephalitis Risks in Regions Affected

While the regions which this disease affects vary from year to year, Japanese Encephalitis is endemic in southern tropical regions of Asia.
The periods of risk are associated with the abundance of the local mosquito population, which is typically highest May to November. However, in some agricultural areas with widespread use of irrigation, the period of risk is year-round.

Japanese Encephalitis will occasionally flare up to produce epidemics. These will be reported on our continually-updated Travel Alerts page on this website.

Please consult this map from the World Health Organization (WHO) showing the countries, highlighted in orange, where Japanese Encephalitis transmission occurs:


Japanese Encephalitis Risks based on Traveler Activities

In the countries affected, Japanese Encephalitis risk is increased in rural agricultural areas and during and after rainy seasons (approximately May to November). The most common mosquito which transmits Japanese Encephalitis bites from dusk until dawn, and so outdoor traveler activities during this period increases risk of infection. In some areas, mosquitos which bite during the day can also transmit this disease.

Travelers with weakened immune systems, pregnant women, seniors and young children are at higher risk for developing the more serious symptoms of Japanese Encephalitis if infected.
If any of the above applies to you, and you are traveling to an affected region, consider getting vaccinated.

Japanese Encephalitis Overview

What is Japanese Encephalitis?

Japanese Encephalitis is caused by a virus which causes swelling of the brain, and is spread by the bite of an infected mosquito.

How do you get Japanese Encephalitis?

The Japanese Encephalitis virus is transmitted by bites from infected mosquitos which typically bite from dusk to dawn, although in some areas it is carried by mosquitos which bite during the day.

What are the symptoms of Japanese Encephalitis?

Most people who contract Japanese Encephalitis show no symptoms. However, when symptoms do occur, they are serious, showing severe neurological symptoms such as paralysis or speech difficulties. Of the cases showing severe symptoms, about 10% - 30% result in death, and 50% of the survivors have permanent or long term neurological damage.

What are the treatments for Japanese Encephalitis?

There is no treatment for Japanese Encephalitis. Therefore getting vaccinated if traveling to affected areas is important.

How can you prevent getting infected with Japanese Encephalitis?

There is a vaccine available which provides 91% - 99% protection from getting infected with Japanese Encephalitis depending on the number of doses received.
Since vaccine protection is not 100% complete, other preventative measures such as protecting yourself from mosquito bites are advised.

Japanese Encephalitis Symptoms

Most people infected do not show any symptoms.
However, if symptoms do appear, they are usually of a serious and often permanent neurological nature, which start appearing 5 to 15 days after infection. Symptoms may start with a sudden onset of headaches, fever and neck stiffness, and may be paired with other severe neurological symptoms such as disorientation, behavioural changes, paralysis, seizures, convulsions, and comas, and may lead to death.
Those who develop these severe symptoms have a 10% - 25% mortality rate, and half of the survivors suffer from permanent neurological damage.

Japanese Encephalitis Prevention

If you are traveling to one of the regions affected and will be conducting activities which put you at higher risk, or you are at higher risk for developing severe symptoms (please see "Risks based on Traveler Activities" section, above), please book an appointment with your local travel medicine center or travel vaccination center for a travel health consultation.

However, while there is a vaccine available to combat Japanese Encephalitis, it is only 91% - 99% effective. Therefore, it is just as important to practice other preventative measures to avoid bites from the mosquitos which carry this disease.

Preventative measures to avoid mosquito bites:

  • Staying in Urban Areas
  • Limiting travel in rural agricultural areas
  • Limiting travel during or after the rainy season (May - November)
  • Discouraging Mosquito Bites by:
    • Cover exposed skin with hats and shoes
    • Wear light-coloured clothing
    • Use mosquito repellent (preferably DEET-based) on exposed skin
    • Apply a permethrin-based insecticide to clothing and tents
    • Sleep under a bed net
    • Stay in a completely-enclosed air-conditioned room
    • Avoid being outside from dusk until dawn