Japanese Encephalitis

What is Japanese Encephalitis?

Japanese encephalitis is a mosquito-borne disease caused by the Japanese encephalitis virus. The incubation period is about 4-14 days. Mild infections may occur without apparent symptoms other than fever with headache. More severe infection is marked by quick onset of headache, high fever, neck stiffness, impaired mental state, coma, tremors, occasional convulsions (especially in children) and paralysis. The case-fatality rate can be as high as 30% among those with symptoms. Of those who survive, 20-30% may have neurological consequences.

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 become infected by feeding on pigs and wild birds infected with the Japanese encephalitis virus. The disease is not directly transmitted from person to person.

How can you prevent the disease?

Avoiding mosquito bites is the first line and the best defense against contracting Japanese encephalitis. The following precautions in preventing mosquito bites should be taken:

• Avoid going to rural areas from dusk till dawn when the mosquitoes spreading this virus are most active
• Wear loose, light-coloured, long-sleeved tops and trousers;
• Avoid using fragrant cosmetics or skin care products;
• Rest in air-conditioned or well-screened rooms;
• Use aerosol insecticide indoor and use bed nets if sleeping areas are not air-conditioned or screened;
• Use insect repellents containing DEET on exposed skin and clothing. For details about the use of insect repellents, please refer to Frequently Asked Questions;
• Re-apply insect repellents according to label instructions;
• If travelling in endemic rural areas, carry a portable bed net and apply permethrin on it as well as to clothes. Permethrin should not be applied to skin.

The second line of defense is vaccination. It is recommended for travellers who plan to stay one month or longer in endemic countries, particularly in rural areas, and for short-term (less than one month) travellers if they plan to have significant extensive outdoor or night-time exposure in rural areas during the transmission seasonof the disease. Please refer to Japanese encephalitis vaccination for more information about the vaccine.

How is it treated?

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

Where is it found?

It occurs mainly in the rural and agricultural areas of Asia and Western Pacific Region. Largely as a result of immunization, its incidence has been declining in Japan and the Republic of Korea and in some regions of China, and more recently in Nepal, Sri Lanka, Thailand and Vietnam. The disease is also reported from Bangladesh, parts of India and Pakistan, and from Cambodia, the Lao People’s Democratic Republic and the Philippines. Transmission is mainly related to the rainy season in Southeast Asia, but year-round transmission occurs, particularly in tropical climate zones. In the temperate regions of China, Japan, the Korean peninsula and eastern parts of the Russian Federation, transmission occurs mainly during the summer and autumn.