Japanese encephalitis - Causes of Japanese encephalitis
- Introduction
- Symptoms of Japanese encephalitis
- Causes of Japanese encephalitis
- Preventing Japanese encephalitis
- Treatment
- Diagnosis
- Vaccination
- Complications
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.
High-risk countries
Japanese encephalitis is found throughout Asia and beyond. The area in which it is found stretches from the Western Pacific islands in the east, such as Fiji, across to the borders of Pakistan in the west. It is found as far north as Korea and as far south as the north coast of Australia.
Most cases occur in
- China
- Myanmar (Burma)
- Thailand
- Vietnam
- Cambodia
- Laos
- Nepal
- India
- Philippines
- Sri Lanka
- Malaysia
- Indonesia
Despite its name, Japanese encephalitis is now relatively rare in Japan, due to mass immunisation programmes.
See the US Centers for Disease Control and Prevention (CDC) website for a map of Japanese encephalitis risk-areas.
Rainy seasons
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 point.
Therefore, it may be useful to find out when the wet seasons are for the areas you are planning to visit before booking your holiday.
High-risk activities
If you are planning a short visit to Asia, the risk of contracting Japanese encephalitis is very low, particularly if you are going to be staying in urban areas. Overall, it is estimated that there is less than one case of Japanese encephalitis for every million travellers.
However, 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 (see above)
- fieldwork, camping or cycling in rural areas
These activities can mean you are more likely to come into contact with infected mosquitoes.
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