Japanese encephalitis is a type of viral brain infection that's 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 when they bite infected animals. It's more common in rural areas where there are pig farms and rice fields. It can't be spread from person to person.
There's currently no cure for Japanese encephalitis. Treatment involves supporting the functions of the body as it tries to fight off the infection. This usually requires the person being admitted to hospital, so they can be given fluids, oxygen and medication to treat any symptoms.
Most people infected by the Japanese encephalitis virus have either no symptoms, or mild, short-lived symptoms, which are often mistaken for flu.
However, around 1 in every 250 people who become infected with Japanese encephalitis develop more severe symptoms, as the infection spreads to the brain. This usually happens 5-15 days after infection and symptoms can include:
- high temperature (fever)
- seizures (fits)
- stiff neck
- inability to speak
- uncontrollable shaking of body parts (tremor)
- muscle weakness or paralysis
Up to one in every three people who develop these more serious symptoms will die as a result of the infection.
In those who survive, these symptoms tend to slowly improve. However, it can take several months to make a full recovery and up to half of those who do survive are left with permanent brain damage. This can lead to long-term problems such as tremors and muscle twitches, personality changes, muscle weakness, learning difficulties and paralysis in one or more limbs.
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.
GOV.UK has information about who to contact when you need immediate medical help abroad. If you're already back in the UK, see your GP.
Your GP or the healthcare professional treating you will ask about your symptoms, where you've been travelling, what you did on your trip and what vaccinations you've 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 visiting risk areas to be affected by Japanese encephalitis. It's estimated that less than one in a million travellers develop Japanese encephalitis in any given year.
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.
Find out more about the causes of Japanese encephalitis and the countries and activities which have a higher risk of catching the disease.
The World Health Organization (WHO) estimates 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 catching it. 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, gives protection against Japanese encephalitis in more than 9 out of 10 people who receive it.
Even if you've 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.
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.