Download PDF Japanese encephalitis

By Alina Ellerington, Encephalitis Society and peer-reviewed by Dr Hannah Brindle and Dr Lance Turtle, University of Liverpool, UK

What is Japanese encephalitis (JE)?

JE is a type of infectious encephalitis caused by Japanese encephalitis virus (JEV). The virus is found in pigs and birds and is transmitted by Culex mosquitoes which breed in water pools and flooded rice fields which bite mainly during the night or just after sunset. The virus cannot be transmitted directly from person-to-person.

JE occurs mostly in South-East Asia and the Western Pacific islands with nearly three billion people living in at-risk areas and over 100,000 estimated cases annually. JE is predominantly seen in children, however, some adults who have no prior immunity may be at risk. A vaccination programme is now in place in several affected countries however, it continues to cause a huge health and economic burden.

Symptoms of Japanese encephalitis

Most people who are infected have only mild or no symptoms, with only about 1 in 250 infections causing brain inflammation. The time from infection to developing symptoms is between 5-15 days. The illness can present with fever, chills, headache, muscle pain and spasm, movement disorders, seizures (particularly in children) and a reduction in the level of consciousness.

Diagnosis of Japanese encephalitis

The symptoms of Japanese encephalitis are not specific for this illness. People living/travelling in the endemic areas should be suspected and tested for JEV if they present with symptoms of encephalitis (fever, seizures, a change in consciousness level or neurological signs). Diagnosis can be confirmed, usually, by finding specific antibodies in the cerebrospinal fluid (CSF) following a lumbar puncture (LP or spinal tap) or in the blood.

Treatment of Japanese encephalitis

There is no specific antiviral treatment for Japanese encephalitis. The treatment is mostly symptomatic and supportive. In the severe cases, the treatment aims to manage seizures and raised intracranial pressure (due to brain inflammation) and support breathing.

Consequences of Japanese encephalitis

JE is a very serious illness. Estimates of death are very variable ranging from 5-50% and nearly half may be left with neurological, psychosocial, cognitive (intellectual) and/or physical disabilities.

Read this article  for more information on patient experience and neurological complications of Japanese encephalitis .


The risk of JE in travellers and people living in endemic areas depends on their destination duration of travel, season, and activities. Those staying for longer periods in rural areas are at greater risk. 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.  In the UK, travellers would be likely to receive one of two vaccines. Talk to your GP or a health clinic before you travel to Asia.

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

WATCH: Chelsea talks about when she contracted Japanese Encephalitis


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FS006V4 Japanese Encephalitis

Date created: March 2002/Last updated: October 2021/ Review date: October 2024

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