Japanese encephalitis

The disease is spread by mosquitoes

The deadly disease Japanese Encephalitis occurs mainly in the rural areas of China and Korea, but is also found in most countries of South and East Asia. Japanese encephalitis is a viral disease spread by mosquitoes, which transfer the virus from infected animals - usually pigs and wading birds - to humans.

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What causes the disease?

Japanese encephalitis is caused by a Flaviviridae virus, which is transmitted by mosquitoes.

Transmission of the disease is most likely during the summer months in temperate areas and during the rainy season and early dry season in tropical areas, when the mosquito populations are the highest.

What are the symptoms?

Most people who are infected show only mild symptoms or no symptoms at all.

However, at advanced stages, the disease may be fatal.

Japanese encephalitis begins like flu with headache, fever, and weakness.

Gastrointestinal problems, including vomiting, as well as confusion and delirium may also be present.

In about one of every 200 cases, the illness progresses to inflammation of the brain, with more than half of those cases ending in permanent disability or death

What treatment is available?

At present, there is no medical "cure" for Japanese encephalitis once infection has occurred.

Pigs are being culled to stop the disease spreading in Malaysia

A vaccine has been developed, but there have been reports of serious allergic side effects in a small number of cases.

About one in five people who receive the vaccine do experience some pain, redness and swelling at the injection site.

About one in ten people also experience one or more of the following reactions:

• Chills
• Muscle pain
• Nausea
• Vomiting
• Abdominal pain

In about one in 260 cases the vaccine causes a general rash, itching or swelling, especially of the extremities, face, lips, and throat.

In rare cases, vaccinees may suffer shock or respiratory distress.

People who have other allergies, especially to bee stings and other drugs, are particularly at risk.

Is there a way to reduce the risk?

The best way to reduce the risk of contracting the disease is to reduce exposure to mosquitoes.

This can be done by avoiding being outside in the cooler hours of dusk and dawn when mosquitoes are most actively feeding.

The use of mosquito repellent, portable bednets, aerosol room insecticides and permethrin, which can be applied to clothing, is also recommended.

Related viruses

Scientists researching the Malaysian outbreak have isolated a mysterious second virus, a member of the Paramyxovirus family, which is believed to have caused some of the deaths.

The new virus is similar to the Hendra virus that killed two people and 15 horses during outbreaks in Australia in 1994 and 1995.

The method of transmission is as yet unclear.

Health experts believe it may be killed through the use of soap, detergent or disinfectant.