Japanese encephalitis is a viral brain infection that is spread through mosquito bites. It is 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 is 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 the hospital so they can be given fluids, oxygen and medication to treat any symptoms.
Key Facts
- Japanese encephalitis is a virus in the flavivirus family. The Culex mosquito passes it on.
- The virus can infect horses and pigs, as well as humans. This can lead to encephalitis in horses and miscarriage in pigs.
- A host is the source of a virus, and the vector passes it on. Wild birds are likely to be the natural hosts of JEV, and mosquitoes are the vectors. A vector does not cause disease but passes it on.
- When mosquitoes infect an animal, the animal might become a carrier of the virus. When other mosquitos feed on these animals that have newly acquired the virus, they take it on board and infect other animals.
- People are at the highest risk in rural areas where the virus is common. Japanese encephalitis is common around towns and cities.
- It is more likely to affect children because adults in areas where the virus is endemic generally become immune as they get older.
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:
- a high temperature (fever)
- seizures (fits)
- a stiff neck
- confusion
- the inability to speak
- uncontrollable shaking of body parts (tremor)
- muscle weakness or paralysis
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.
Causes
Japanese encephalitis is caused by a flavivirus, which can affect both humans and animals. The virus is passed from animals to humans through the bite of an infected mosquito.
Pigs and wading birds are the main carriers of the Japanese encephalitis virus.
A mosquito becomes infected after sucking the blood from an infected animal or bird.
If you get bitten by an infected mosquito, it can pass on the virus.
The mosquitoes that carry Japanese encephalitis usually breed in rural areas, particularly where there are flooded rice fields or marshes, although infected mosquitoes have also been found in urban areas.
They usually feed between sunset and sunrise.
Japanese encephalitis cannot be passed from person to person.
Prevention
The best way to prevent Japanese encephalitis is to be vaccinated against the infection before you visit a part of the world where there is a risk of catching it.
The risk is greater if you are 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:
- sleeping in rooms with close-fitting gauze over the windows and doors – if you’re sleeping outside, use a mosquito net that has been impregnated with insecticide
- covering up with long-sleeved tops, trousers and socks
- applying a good-quality insect repellent to exposed areas of skin
There is no treatment or cure for Japanese encephalitis.
Once a person has the disease, treatment can only relieve the symptoms. Antibiotics are not effective against viruses, and effective anti-viral drugs are available.
Prevention is the best form of treatment for Japanese encephalitis.
The main therapy is supportive care. There are medications to help the swelling in the brain, and sometimes a person might require heavy sedation and a breathing tube for a period of time until the swelling in the brain begins to improve
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