Japanese Encephalitis

What is Japanese Encephalitis (JE)?

Japanese Encephalitis is a mosquito-borne disease caused by the Japanese Encephalitis virus. It occurs mainly in the rural and agricultural areas of Asia and Western Pacific. Over 50,000 cases are reported annually from Southeast Asia, India, China, Japan and Korea. In temperate regions such as China, Japan and Korea, the transmission is highest from April to September. In northern India and Nepal, peak transmission is from June to November. In the tropical regions of Asia and Oceania, JE occurs year-round.

Most infections are asymptomatic. Only 1 in 250 infected individuals becomes sick . The incubation period is about 4-14 days. Usual symptoms include headache, fever, nausea and vomiting. Severe cases may progress to confusion and coma. The mortality can be as high as 35%. About 30% of those who survive may have severe nervous system damage like paralysis.

How does it spread?

The virus is transmitted by the bite of infected Culex mosquitoes. The mosquitoes breed where there is abundant water such as rice paddies and feed mainly on domestic animals such as pigs. About 1-3% of the Culex mosquitoes in endemic areas are infective.

How can you prevent the disease?

Travellers can protect themselves by taking simple precautionary measures such as avoiding outdoor exposure to mosquito bites at dusk and dawn, especially in rural areas, and apply effective insect repellents with DEET to exposed parts of their bodies. The concentration of DEET applied depends on the types of activities and occasions. In general, a concentration of up to 35% is effective. The higher the concentration, the longer lasting is the application. However, travellers should avoid over dosing the application.

Vaccines are available which consist of 3 doses on days 0, 7 and 30. The course should be completed at least 10 days before departure. There is a 20% chance that one may develop localized tenderness, redness or swelling at the injection site. The vaccine is indicated mainly for persons spending 30 days or more in a rural agricultural endemic area during the transmission season.

How is it treated?

There is no specific treatment for this disease. The mainstay of treatment is symptomatic and supportive.

[Japanese Encephalitis, 2006]



Last revision date: 10 October 2012