Download PDF Japanese encephalitis

By Alina Ellerington, Encephalitis Society

What is Japanese encephalitis (JE)?

Japanese encephalitis is a type of infectious encephalitis caused by Japanese encephalitis virus. The virus is found in pigs and birds and is transmitted by Culex mosquitoes which breed in water pools and flooded rice fields and bite mainly during the night. The virus cannot be transmitted person-to-person.

Japanese encephalitis occurs in Asia, mostly in South-East Asia, the Pacific islands and the Far East with nearly three billion people living in at-risk areas and about 68,000 cases annually. Anybody can get infected with the virus. Where JE childhood vaccination programmes are in place, children cases have diminished as a result. Some adults have developed natural immunity after childhood infection. However, JE still causes a huge health and economic burden.

Symptoms of Japanese encephalitis

Most people with the infection do not have any symptoms. Only 1 in 250 cases has a severe course of the disease. The time from infection to developing symptoms is between four to 14 days. The illness can manifest with fever, chills, headache, muscle pain and spasm, confusion, movement disorders and seizures. If children are affected, the illness usually starts with gastrointestinal pain and vomiting. Disease may rapidly progress to severe alteration of consciousness (coma).

Diagnosis of Japanese encephalitis

Symptoms of JE are not specific for this illness. People living/travelling in the endemic areas should be suspected and tested for JE if they present with symptoms of encephalitis. Diagnosis can be confirmed, usually, by finding specific antibodies in the cerebrospinal fluid (CSF) by doing a lumbar puncture (LP or spinal tap) or in the blood.

Treatment of Japanese encephalitis

There is no specific antiviral treatment for JE. Treatment is mostly symptomatic and supportive. In the severe cases treatment aims to manage seizures, raised intracranial pressure (because of brain inflammation) and breathing.

Consequences of Japanese encephalitis

It is estimated that death occurs in 20-30% of the patients (high risk in children under 10) and up to 30% of the severe cases are left with neurologic, psychosocial, cognitive (intellectual) and/or physical disabilities, with a higher rate of problems reported in children.

Prevention of Japanese encephalitis

The risk of JE in travellers and people living in endemic areas depends on destination (rural areas are at high risk), duration of travel, season, and activities. Prevention consists of general prevention measures and vaccination.

  • General measures of prevention against mosquito bites: using repellent, bed nets, wearing adequate clothing (long sleeves/trousers).
  • Vaccination. There are three types of vaccine recommended by the World Health Organisation. Talk to you GP or a health clinic before you travel to Asia.

More information on prevention and guidelines for travellers is provided on our website 


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FS006V3 Japanese Encephalitis

Date created: March 2002/Last updated: December 2017/ Review date: December 2020

Disclaimer: We try to ensure that the information is easy to understand, accurate and up-to-date as possible. If you would like more information on the source material the author used to write this document please contact the Encephalitis Society. None of the authors of the above document has declared any conflict of interest which may arise from being named as an author of this document