Questions and answers about Japanese encephalitis

Related program: Center for Vaccine Innovation and Access

Japanese encephalitis (JE) is an inflammation of the brain caused by the JE virus, which is transmitted to humans by mosquitoes. JE kills up to 30 percent of those who develop the disease, mostly children. Among survivors, half are left with permanent brain damage, such as paralysis, seizures, inability to speak, memory loss, impaired cognition, and other mental disorders. Because of this, JE is Asia’s most common cause of viral neurological disability.

What is Japanese encephalitis?

Japanese encephalitis (JE) is a viral infection that affects parts of the central nervous system, including the brain and spinal cord. It is the leading cause of viral neurological disease and disability in Asia, and it is especially prevalent among children. There is no cure for JE. Vaccination is the only viable way to prevent the disease.

How do people get JE?

JE is caused by a virus spread by mosquitoes. The virus first infects animals, such as pigs and birds. When a mosquito bites an infected animal and then bites a human, the person can become infected with the JE virus. People do not transmit the disease to each other.

Who is at risk for JE?

More than 3 billion people live in parts of Asia that are at risk for JE. The endemic region includes Southeast Asia and parts of the Western Pacific—from India and Bangladesh through China and Japan and south to Papua New Guinea and the islands of the Torres Strait in Australia.

While adults can get JE, children younger than 15 years old are at higher risk. After that age, most people are immune due to past exposure to the JE virus.

Because mosquitoes that spread JE live in rice fields and other pools of water common in the countryside, people who live in rural areas are most at risk. In addition, animals such as pigs and wading birds that are part of the JE transmission cycle are common in rural areas. People who live in cities—where mosquitoes that spread JE breed in standing puddles, open sewers, and fish ponds—can also get JE.

How many people does JE affect?

Nearly 70,000 cases and approximately 10,000 to 15,000 deaths are attributed to JE each year. However, because of limited surveillance and the complexity of diagnosis, it is likely that these figures significantly underestimate JE’s impact.

What are the symptoms of JE?

The illness usually begins just like the flu, with high fever, chills, tiredness, severe headache, nausea, and vomiting. In the early stages, people can be confused, agitated, or unusually sleepy. The illness can progress to a serious infection of the brain, which can cause seizures or leave people semiconscious, comatose, or unresponsive.

How is JE diagnosed?

JE is diagnosed by testing blood and spinal fluid.

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 treating symptoms and preventing complications. Vaccination is the most effective way to protect people from the disease.

What are the side effects of JE?

Up to 30 percent of people who get JE die, but the disease extracts a heavy, and perhaps less recognized, toll on its survivors, too. Roughly 70 percent of children with JE either die or suffer from disabilities that will affect them for the rest of their lives, including intellectual, behavioral, or neurological problems such as paralysis, recurrent seizures, or the inability to speak. Up to half of all survivors are left with these kinds of disabilities.

How can JE be prevented?

Immunization is the best way to prevent JE. Avoiding mosquito bites can also reduce the risk of disease. Unfortunately, vaccination does not help a child already infected with or ill from JE. The World Health Organization and other JE authorities recommend that all at-risk people receive a safe and efficacious vaccine as part of their national immunization program.