Japanese encephalitis


Japanese encephalitis is a type of viral brain infection that is spread through mosquito bites. It’s common in rural areas throughout Southeast Asia, the Pacific islands and the Far East.

The virus is found in pigs and birds, and is passed to mosquitoes that bite the infected animals. It’s more common in rural areas where there are pig farms and rice fields. It cannot be spread from human to human.

Read more about the causes of Japanese encephalitis.

Most people who are infected by the Japanese encephalitis virus do not develop any symptoms, or they get only mild, flu-like symptoms.

However, around one person in 250 infected by the virus has serious and severe symptoms, including:

  • being sick
  • seizures (fits)
  • headache 
  • mental confusion

The virus can cause swelling inside the brain (encephalitis), leading to increased pressure in the brain. This can cause permanent brain damage. Around one in three cases of encephalitis is fatal.

Read more about the symptoms of Japanese encephalitis.


There is currently no cure for Japanese encephalitis so treatment involves supporting the functions of the body as it tries to fight of the infection. This will usually involve admission to hospital.

A medication called mannitol can be used to reduce pressure inside the brain, which can sometimes prevent permanent brain damage.

Read more about the treatment of Japanese encephalitis.

Who is affected?

It’s rare for travellers from outside the region to be affected by Japanese encephalitis. It is estimated that only one in 1 million travellers will develop Japanese encephalitis in any year.

People who live and work in rural areas in parts of the world where the condition is widespread are most at risk. Around 9 out of 10 cases involve children under the age of 15 years.

There are an estimated 70,000 new cases every year, half of which occur in China.


Two vaccines are available for Japanese encephalitis. Vaccination is normally recommended if:

  • You are planning to spend a month or longer in a high-risk country during the rainy season.
  • You are planning to visit any rural areas in high-risk countries, even if only for a short time.
  • You will be taking part in any activities that may increase your risk of becoming infected, such as visiting rice fields or pig farms, cycling or camping.

You will normally have to pay for the vaccine.

Read more about vaccines for Japanese encephalitis.


Encephalitis is inflammation of the brain. This can develop as a result of infection (usually viral) or when the immune system attacks the tissue of the brain by mistake (post-infectious encephalitis).

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Immune system
The immune system is the body's defence system, which helps to protect it from disease, bacteria and viruses.

The electrical impulses in the brain are disrupted, causing both the brain and the body to behave strangely.

Last updated: 13 June 2012

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