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17 August 2015
Japanese Encephalitis  

What is Japanese encephalitis
Japanese encephalitis is a mosquito-borne disease caused by the Japanese encephalitis virus. The virus is transmitted by the bite of infected mosquitoes . The principal type of mosquito that transmits the disease is called Culex tritaeniorhynchus. The disease occurs mainly in the rural and agricultural areas of Asia and the Western Pacific Region. It is an uncommon disease in Hong Kong.

Mode of transmission
The infected mosquito transmits the virus to humans and animals during biting. 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.

Signs and symptoms
Symptoms usually start at around 4-14 days after being infected. 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.

Treatment and complications
There is no specific treatment for this disease. Supportive therapy is indicated. Death rates may range from 5% to 35%. Patients who survive may have neurological consequences.

How to prevent the disease
Japanese encephalitis has caused epidemics in China, Korea, Japan, Taiwan and Thailand in the past but is now controlled primarily by vaccination. However, some countries still have periodic epidemics of the disease. These include Vietnam, Cambodia, Myanmar, India, Nepal and Malaysia. To prevent contracting the disease, one should take general measures to prevent mosquito bites, apply effective insect repellents (containing DEET) to exposed parts of the body and avoid going to rural areas from dusk till dawn when the mosquitoes spreading this virus are most active.

Vaccines for Japanese Encephalitis
There is a vaccine for Japanese encephalitis but it is usually not recommended for members of the general public. The vaccine is only recommended for travellers who plan to stay one month or longer in endemic areas in Asia and Western Pacific Region, 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 season of the disease . For further information on Japanese encephalitis vaccination and outbreak news in other countries, please visit the Hong Kong Travellers' Health Service website at

General Measures on Preventing Mosquito-borne Diseases

1. Wear loose, light-coloured,long-sleeved tops and trousers, and apply effective insect repellents containing DEET to exposed parts of the body & clothing.

2. Use mosquito screens or bed nets when the room is not air-conditioned.

3. Apply household pesticide to kill adult mosquito with a dosage according to the label instructions. Do not spray the pesticides directly against functioning electrical appliances or flame to avoid explosion.

4. Place mosquito coil or electric mosquito mat / liquid near possible entrance, such as window, to prevent mosquito bites.

5. Prevent the accumulation of stagnant water
- Put all used cans and bottles into covered dustbins.
- Change water for plants at least once a week, leaving no water in the saucers underneath flower pots.
- Cover tightly all water containers, wells and water storage tanks.
- Ensure air-conditioner drip trays are free of stagnant water.
- Keep all drains free from blockage.
- Top up all defective ground surfaces to prevent the accumulation of stagnant water.

For details about the use of insect repellents, please refer to 'Tips for using insect repellents'.

For more information about control and prevention of mosquito breeding, please visit the website of Food and Environmental Hygiene Department (FEHD) at

If you notice any mosquito breeding sites in public places, you may call the FEHD's Hotline at 2868 0000.

Related link: World Health Day 2014

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