What is Japanese encephalitis?

Japanese encephalitis (JE) is a severe disease that causes encephalitis, or infection of the brain. Some people recover fully, but the disease can cause serious problems like seizures or paralysis, and some patients die. JE is the leading cause of viral encephalitis in Asia.

How do people get JE?

JE is caused by a virus spread by mosquitoes. The virus infects animals like pigs and birds. If a mosquito bites an infected animal and then bites a human, the person can become infected with the JE virus. After a person is bitten by a mosquito, the JE 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 areas, 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 like pigs and wading birds (such as 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 (e.g., standing puddles, open sewers, fish ponds).

The disease is most frequently seen in children between the ages of 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. However, it is thought many more cases and deaths occur than are actually reported.

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 and cannot be awakened.

What is the treatment for JE?

While 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 effective antiviral medicines 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 been most widely available internationally is an inactivated mouse brain-derived vaccine. But it is labor intensive to produce, there is not enough available for everyone who needs it, and production of this vaccine has stopped in many places. So 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 over 20 years in China but has only recently become available internationally. With the development and wider availability of improved vaccines, there are now better prospects for the control of JE in Asia.