Japanese encephalitis (JE) is a viral infection of the brain transmitted to humans by mosquitoes in parts of Asia and the Pacific Rim. The mosquitoes that transmit JE feed predominantly during the night, between dusk to dawn and are prolific in rural areas, where rice cultivation and pig farming are common. However, they have also been found in urban locations.

The risk for most travellers to Asia is very low, especially for short-term travellers visiting urban areas. The overall incidence of JE among persons from non-affected countries travelling to Asia is estimated to be less than one case per 1 million travellers. Risk varies based on: destination, duration, season and activities. It increases for persons who intend to live or travel in risk areas for long periods and to rural areas. Certain activities, even during short trips, where there is significant rural, outdoor or nighttime exposure e.g. fieldwork or camping can increase the traveller’s risk.

Most human infections with JE virus do not result in symptoms. When symptoms do occur, they include fever, headache and confusion. In symptomatic cases requiring hospitalisation death rates are high and neurological complications are common.