What is Japanese encephalitis?

Japanese encephalitis (JE) is a severe disease that involves inflammation of the brain. Some people recover fully, but the disease can cause serious problems such as seizures or paralysis, and some patients die.

How do people get JE?

JE is caused by a virus spread by mosquitoes. The virus infects animals such as pigs and birds. If a mosquito bites an infected animal and then bites a human, the person can become infected with the virus. After the person is infected, the virus invades parts of the central nervous system, including the brain and spinal cord, and symptoms then occur.

Who is at risk for JE?

Countries with JE risk include those in Asia and parts of the Western Pacific Region, from Pakistan and India through China and Japan and south to Papua New Guinea and the islands of the Torres Strait in Australia.

In endemic regions, people living in rural areas are most at risk. They are more often exposed to bites from infected mosquitoes because the mosquitoes that spread JE commonly live in rice fields and other pools of water. Animals such as pigs and wading birds (including herons and egrets) are also common in rural areas and are part of the JE transmission cycle.

Cases of JE also occur in cities. The mosquitoes that spread JE in urban areas breed in contaminated water (for example, standing puddles, open sewers, and fish ponds).

The disease is most frequently seen in children aged 1 to 15 years, although anyone can get JE.

How many people does it affect?

Approximately 30,000 to 50,000 cases and 10,000 deaths are reported each year. These number probably underestimate the true toll of the disease, however, because many cases are unreported.

What are the symptoms of JE?

• The illness usually begins just like the flu with high fever, chills, tiredness, severe headache, nausea, and vomiting.
• A person may show abnormal behavior or become confused and agitated, or a child may be unusually sleepy.
• A person may develop seizures, become semiconscious, or become comatose.

What is the treatment for JE?

Although there is no specific treatment for JE, supportive care in a medical facility is important to reduce the risk of death or disability. Patient care involves preventing and treating symptoms and complications. Antibiotics are not effective against viruses, and no antiviral medicines effective against JE have been discovered.

What is the outcome of JE?

Up to 30 percent of people who get JE die. About 40 percent more have some sort of disability, including paralysis, mental retardation, recurrent seizures, or personality changes.

How can JE be prevented?

Immunization is the best way to prevent JE. Avoiding mosquito bites can also reduce the risk of disease. Unfortunately, JE vaccine does not help a child already infected or ill from JE.

The JE vaccine that has historically been most widely available is labor intensive to produce. Production has stopped in many places, and there is not enough of this vaccine available for everyone who needs it. Recent work has focused on developing and distributing newer vaccines that are easier and less expensive to produce, are more efficacious, have fewer side effects, and are easier to integrate into routine immunization schedules. This includes one that has been used for more than 20 years in China and is now available internationally. With the development and wider availability of improved vaccines, prospects for controlling JE in Asia have improved.