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Japanese encephalitis is a type of viral brain infection that's spread through mosquito bites.
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.
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.
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.
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.
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.
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.
Japanese encephalitis is found throughout Asia and beyond. The area in which it's found stretches from the Western Pacific islands in the east, such as Fiji, across to the borders of Pakistan in the west. It's found as far north as parts of Russia and as far south as the north coast of Australia.
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.
Sleeping in rooms with close-fitting gauze over the windows and doors.
Sleeping under a mosquito net may help prevent being bitten by an infected mosquito.
Covering your skin or using bug sprays containing DEET may also help prevent infection.
Insect repellent clothing and accessories are also a great protection from unwanted bites.