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.
Japanese encephalitis is found throughout Asia and beyond.
Most cases occur in:
- Myanmar (Burma)
- Sri Lanka
Despite its name, Japanese encephalitis is now relatively rare in Japan as a result of mass immunisation programmes.
The US Centers for Disease Control and Prevention (CDC) website has a map showing Japanese encephalitis risk areas.
The risk of becoming infected with Japanese encephalitis is highest during and just after rainy seasons.
This is because mosquito populations tend to increase suddenly around this time.
There's also a risk of getting Japanese encephalitis in countries with a year-round tropical climate.
TravelHealthPro has more information about the country you're travelling to.
If you're planning a short visit to Asia, the risk of getting Japanese encephalitis is very low, particularly if you're going to be staying in urban areas.
Overall, it's estimated there's less than 1 case of Japanese encephalitis for every million travellers.
But there are certain activities that can increase your risk of becoming infected, such as:
- living or travelling in high-risk areas for a long time
- visiting rural areas, particularly during the rainy season
- camping, cycling or working outdoors in rural areas
These activities can mean you're more likely to come into contact with infected mosquitoes.