Japanese encephalitis: symptoms, risk for travellers and vaccination

The NHS says Japanese encephalitis is a rare but serious infection that you can get from mosquito bites in some parts of the world. It is caused by a virus which is spread through mosquito bites.

TravelHealthPro, the UK travel health service for professionals and the public, describes it as a viral infection of the brain transmitted to humans by mosquitoes in parts of Asia and the Western Pacific. The UK Health Security Agency's Green Book chapter on the disease says it is the leading cause of childhood encephalitis in Asia, with an estimated 68,000 clinical cases per year.

The NHS says most people who get Japanese encephalitis have no symptoms. Some people get flu-like symptoms, which usually go away on their own. In some people the infection spreads to the brain and causes more serious symptoms.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you have recently travelled to an area where Japanese encephalitis is found and you have flu-like symptoms such as a headache, a high temperature, feeling or being sick or tummy pain. Tell anyone you speak to about your recent travel, and if you were bitten by a mosquito or might have been.

Call 999 if you or someone else has a severe headache and a stiff neck, sudden confusion, sudden weakness or sudden inability to feel or move part of the body, a seizure, loss of consciousness or severe difficulty breathing. Do not drive to A&E. Get medical advice quickly if you have symptoms while you are travelling.

The NHS says you will need to be treated in hospital if you are seriously unwell because Japanese encephalitis can be life-threatening. Treatments include medicines to help relieve the symptoms, such as painkillers and steroids. It can sometimes cause long-term complications such as paralysis, seizures and loss of speech.

TravelHealthPro says that in symptomatic cases requiring hospitalisation, death rates are high and neurological complications are common.

TravelHealthPro says the mosquitoes that transmit the virus feed mostly at night, between dusk and dawn, and are prolific in rural areas where rice cultivation and pig farming are common, although they may also be found in peri-urban locations. The Green Book update notes that cases are also reported outside the normal seasonal period of high transmission.

It says the risk for most travellers to Asia is very low, especially for short-term travellers visiting urban areas, with an overall incidence among people from non-affected countries estimated at less than one case per 1 million travellers. The risk depends on destination, duration of travel, season and activities, and increases for people who live or travel in risk areas for long periods and visit rural areas. Certain activities, even on short trips, with significant rural, outdoor or night-time exposure, such as fieldwork or camping, can increase the risk.

You can check the risk for the country you are visiting on the TravelHealthPro website, as the NHS suggests.

The NHS says a vaccine is recommended if you are travelling to a part of the world where the virus is found, especially if you are staying for more than a month, staying in a rural area, or staying near or visiting rice fields, wetlands or places where pigs are kept. TravelHealthPro adds that the vaccine is recommended for people at increased risk of exposure during travel or through their occupation.

The NHS says you have to pay for the vaccine, which you can get from travel health clinics and pharmacies with travel health services. A travel vaccination clinic can advise before you travel.

TravelHealthPro says a licensed vaccine, IXIARO, is available in the UK. The standard primary course is two doses given on day 0 and day 28.

TravelHealthPro says the primary course should be completed at least one week before potential exposure to the virus. It is not usually recommended under 2 months of age because there are no safety or efficacy data. IXIARO is only available in a small number of Asian countries, so travellers may not be able to complete a course overseas with this vaccine, and those who start with IXIARO should complete the primary course with it.

If a course is interrupted, TravelHealthPro says the schedule should be resumed, not restarted. Talk to a travel health professional, who uses the UKHSA Green Book guidance, about whether the vaccine is right for you.

TravelHealthPro says the risk of Japanese encephalitis can be reduced by insect bite avoidance, particularly between dusk and dawn, when Culex mosquitoes are most active. The NHS gives practical steps.

• Use insect repellent on exposed skin, ideally containing at least 50% DEET.

• Sleep under a mosquito net treated with insecticide when possible.

• Wear long-sleeved tops, trousers or long skirts, socks and shoes to protect your skin.

• Get advice from a travel vaccination clinic before you travel.

The NHS says the vaccine is not free, so it is usually obtained from a travel health clinic or a pharmacy with travel health services, many of which are private.

If you become unwell after travel, the NHS route is a GP, NHS 111 or, for severe symptoms, 999.