Japanese encephalitis Vaccination

The mosquito-borne virus Japanese encephalitis can result in permanent neurological damage. Mosquitoes can become infected when they bite an infected bird or animal, and then if they bite you, they can pass the virus on. Most cases of JE are mild, but less than 1% of cases result in encephalitis (brain swelling), and between 20% and 30% of those patients will die. The World Health Organization says that a literature review shows 68,000 clinical cases every year.

Symptoms of Japanese encephalitis

Five to fifteen days after being bitten by an infected mosquito, the patient suffers from flu-like symptoms, although many people have no symptoms. If you are travelling or have just returned from travelling, particularly in the tropics, any flu-like illness is a cause for concern and you should seek medical advice and tell your healthcare professional where you have visited. In severe cases (about one in 250), there will be encephalitis (swelling of the brain), high fever, convulsions, headaches and paralysis. About one in three cases that progress to encephalitis prove fatal.

Countries where Japanese encephalitis is a risk

This disease occurs in almost all Southeast Asia and parts of the western Pacific. The type of mosquito associated with JE breeds in rice paddies, near pig farms and wherever there is irrigation. The US Centers for Disease Control has a map showing the distribution of JE. It is rare in Japan, however, because of an immunization program.

Which travellers are at risk from Japanese encephalitis?

The following travellers should consider themselves at elevated risk of being bitten by a mosquito carrying JE:

• anyone visiting a high-risk area during the rainy season
• anyone staying near rice paddies, marshland or pig farms
• anyone planning outdoor activities such as hiking, cycling, camping or fieldwork
• anyone on a prolonged visit to an at-risk area

Ways to avoid catching Japanese encephalitis

The JE shot provides protection from this virus up to a point, but it is important to back up the vaccine by practising mosquito-avoidance. The mosquitoes which transmit JE prefer a warm and humid environment and are most active at dusk. You can avoid mosquito bites by:

• covering up with loose clothing (think trousers, long-sleeved top and socks)
• use an insecticide in your room before you go to bed and ensure your room is screened or your bed netted
• apply insect repellents (50% DEET) to your skin