Japanese Encephalitis

Japanese Encephalitis (JE) is a potentially fatal brain infection caused by a virus transmitted by mosquitoes. Most have a mild illness, but of those who become ill, recovery may be associated with neurological complications or death. Despite its name, the illness is uncommon in Japan, restricted to rural areas in the summer months. In more southern, equatorial countries it is a year-round risk, though higher in the wet season. The Culex mosquito which spreads the disease is mainly active in rural areas, and travellers most at risk are those spending extended time outside cities and towns. Waterbirds and pigs are involved in the virus’ life cycle, and farming areas, especially rice paddies, are higher risk areas.

The infection is confined to Asia, from Pakistan in the west, across to Papua New Guinea in the east, and as far north as Russia and Japan. Presently, there is some risk of the disease in the popular tourist destination of Bali. The Indonesian government have recently opted to immunise all local children as a precaution.


Often a mild illness with fever and resolution, however in some it can develop into encephalitis (infection of the brain and nervous system) with resulting headaches, confusion, nausea, vomiting and coma with variable outcomes. The rule of thirds usually applies. 1/3 recover fully, 1/3 die, 1/3 are left with a neurological deficit.


First line protection is based around mosquito bite prevention particularly dusk, dawn and overnight, using DEET based insect repellents on exposed skin, permethrin impregnation of clothing and mosquito nets, mosquito coils and screened accommodation. For higher risk travel two effective Japanese encephalitis vaccines are available.


  • When should I vaccinate?

    Vaccinating for JE is often a tricky decision, mainly as a result of vaccine cost and varying risk/benefit. It is mostly recommended for longer term travellers to Asia in risk areas and in the wet season, however there have been cases in those on short term resort holidays. It is one of the least common mosquito borne illnesses, however the consequences can be large and there is no medication available to treat it.

  • Which vaccine should I have?

    This is a decision made best with our Travel Doctors, depending on medical history, duration of travel, age and budget. There is a single vaccine which provides at least 5 years’ protection, or a less expensive two dose schedule providing protection for at least a year with boosters as necessary. Protection against the disease is not fully achieved until around 7 days after vaccination.