Japanese encephalitis

Japanese encephalitis (JE) is a viral disease caused by a type of virus called a flavivirus. It is spread through the bite of an infected mosquito. In most cases, the illness is mild, with symptoms including headaches and a high temperature (fever).

Serious symptoms

JE can cause more serious symptoms, such as vomiting or seizures (convulsions). Encephalitis (inflammation of the brain) can develop in around 1 in 300 cases. Among those who develop more serious symptoms, there is around a 30% chance that JE can be fatal.

JE occurs throughout Southeast Asia, the Far East and the Pacific islands. The virus is found in pigs and birds, and is passed to mosquitoes that bite the infected animals. JE is more common in areas where there are pig farms and rice fields, both of which are ideal breeding grounds for mosquitoes.

JE is usually seasonal, occurring during the rainy season, and varies from country to country.

How common is Japanese encephalitis?

According to the World Health Organization (WHO), at least 50,000 people in Asia develop visible symptoms of Japanese encephalitis each year. Around 1 in 200 people develop more serious symptoms, which can lead to permanent brain damage or death.

Travellers are very rarely affected by JE. The American Center for Disease Control estimates that there is less than one case of JE for every million travellers. There have also only been two documented cases of UK travellers contracting JE, one in 1982 and one in 1994.

Outlook

Anyone who catches JE and recovers will develop immunity (resistance) to the virus. This means that if they become infected again, they should not experience any severe symptoms.

In areas where JE is common, older children and adults are often immune to JE. The more serious complications usually occur in young children who have caught JE for the first time. 

WHO estimates that there are around 10,000 deaths from JE every year, mainly in children.

There is currently no specific treatment for the virus that causes JE. However, a vaccination is available for travellers who may be at risk of catching the disease.

Glossary

Seizures
The electrical impulses in the brain are disrupted, causing both the brain and the body to behave strangely.

Encephalitis
Encephalitis is inflammation of the brain. This can develop as a result of infection (usually viral) or when the immune system attacks the tissue of the brain by mistake (post-infectious encephalitis).

Inflammation
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Brain
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.

Immune system
The immune system is the body's defence system, which helps to protect it from disease, bacteria and viruses.