Japanese encephalitis is a viral brain infection that's spread through mosquito bites. It's most common in rural areas in southeast 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 cannot 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.
The person usually needs to be 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.
But 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 to 15 days after infection.
Symptoms can include:
Up to 1 in every 3 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.
But 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 1 or more limbs.
You should get immediate medical advice if you have any of the symptoms of Japanese encephalitis and you 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 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.
It's very rare for travellers visiting risk areas to be affected by Japanese encephalitis.
It's estimated less than 1 in a million travellers get Japanese encephalitis in any given year.
The World Health Organization (WHO) estimates there are around 68,000 cases of Japanese encephalitis worldwide each year.
The people most at risk are those who live and work in rural areas, such as on pig farms and in rice fields, 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 which countries have the highest risk.
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 have been vaccinated, you should still take precautions to reduce your risk of being bitten by an infected mosquito, such as:
It's a good idea to keep a list of important telephone numbers with you when travelling abroad.
These should include numbers for: