Japanese encephalitis

Japanese encephalitis is a type of viral brain infection that is spread through mosquito bites. It's most common in rural areas throughout South East Asia, the Pacific islands and the Far East, but is very rare in travellers.

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 person to person.

Read more about the causes of Japanese encephalitis.

Signs and symptoms

Most people infected by the Japanese encephalitis virus have either no symptoms, or mild symptoms that are short-lived and flu-like.

In less than 1 in every 250 cases, the infection can spread to the brain (encephalitis) and cause more serious symptoms, such as:

  • seizures (fits)
  • confusion
  • inability to speak
  • paralysis (inability to move certain body parts)

There is currently no cure for Japanese encephalitis. Treatment involves supporting the functions of the body as it tries to fight off the infection. This will usually require the person being admitted to hospital, where you can be given fluids, oxygen and medication to treat any symptoms.

Up to one in every three people who develop more serious symptoms will die, and many of those who survive are left with permanent brain damage.

Read more about the symptoms of Japanese encephalitis.

When to seek medical advice

You should seek immediate medical advice if you have any of the symptoms of Japanese encephalitis and have recently visited, or are still in, an area where the infection is found.

For information about who to contact when you need immediate medical help abroad, visit the GOV.UK website. If you are already back in the UK, see your GP.

Your GP or the healthcare professional treating you will ask about your symptoms, where you have been travelling, what you did on your trip and what vaccinations you have had. If necessary, they may carry out a blood test to see if you have an infection.

How common is Japanese encephalitis?

It’s very rare for travellers from outside risk areas to be affected by Japanese encephalitis. It is estimated that less than one in a million travellers will develop Japanese encephalitis in any given year. There has not been a reported case in a traveller returning to the UK for over 10 years.

The people most at risk are those who live and work in rural areas where the condition is widespread. Around 75% of cases involve children under the age of 15.

The World Health Organization (WHO) estimates that there are around 68,000 cases of Japanese encephalitis worldwide each year.

Preventing Japanese encephalitis

The best way to prevent Japanese encephalitis is to be vaccinated against the infection before you visit a part of the world where there's a risk of infection. The risk is greater if you're planning to visit rural areas or go hiking or camping.

The vaccine, which is usually only available privately, provides protection against Japanese encephalitis in more than 9 out of 10 people who receive it.

Even if you have been vaccinated, you should still take precautions to reduce your risk of being bitten by an infected mosquito, such as:

  • sleeping in rooms with close-fitting gauze over the windows and doors. If you're sleeping outside, use mosquito nets that have been impregnated with an insecticide
  • covering up with long-sleeved tops, trousers and socks
  • applying a good quality insect repellent to exposed areas of skin

Read more about preventing 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.

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