Japanese Encephalitis

Japanese Encephalitis vaccine is one of the more commonly requested travel vaccinations we provide at TrExMed Travel Clinic Edinburgh.

Japanese Encephalitis virus (JEV) is a potentially serious infection, which is endemic in 24 Asian countries.  It is mainly transmitted by Culex mosquitoes, which typically bite in the evening and early morning.  Although local cases are declining in Japan, South Korea and some parts of China with vaccination, it is increasingly being reported from Bangladesh, Myanmar, parts of India, Nepal, parts of Pakistan, northern Thailand and Vietnam.

The natural hosts for the virus are water birds, such as herons, egrets and ducks.  It is spread to people by mosquito bites, although domestic pigs may also act as an intermediary host and amplify the infection near to people's homes.  This may then lead to unpredictable outbreaks of human infection, particularly among younger children who have no immunity.

This is the 'textbook' disease pattern of Japanese Encephalitis, and how it typically affects local communities in rural areas, especially near paddy fields in the monsoon season.

The evidence for risk among travellers

Recent evidence, looking at travellers who develop the disease, reveals quite a different risk pattern: There have been at least 21 confirmed cases among visitors to Thailand returning to Western countries reported between 1992 and 2013 (i.e. about one per year).  Of these, most had only been to Bangkok and/or the tourist islands, 71% had been short-term travellers (4 weeks or less) and a third had been infected in the dry season.

How serious is Japanese Encephalitis disease?

Although most infections go unnoticed, in about one in 250 people, the virus can penetrate through to the brain, causing severe headache, high fever, meningitis and/or encephalitis.

Most such severe cases will require hospitalisation with intensive care. Typically, among young adults a third of cases are fatal, a third go on to have permanent symptoms or signs of neurological damage, and the remaining third make a full recovery.  The disease is more serious in the elderly (50% case fatality rate over 60 yrs).

Among travellers, Japanese Encephalitis (the disease) is more common and has a higher case fatality rate than its Western cousin, Yellow Fever.

Japanese Encephalitis prevention

  • Fortunately, there is a very safe and effective vaccine available, called: Ixiaro. This is now licensed in Europe to be given in a primary course of two doses, one week apart.  A third, booster dose is recommended 1-2 years later, if planning to return to an endemic risk area.
  • [For those whose itinerary permits, there is also a different, 'live' vaccine, called: Imojev, which is licensed only in Australia and parts of SE Asia...]
  • Avoid getting bitten!  Use insect repellents and cover up exposed skin in at-risk areas.  Even if you are protected against Japanese Encephalitis you may still be at risk from dengue, chikungunya and zika viruses (all spread by aggressive day-biting mosquitoes), for which there are no vaccines licensed for travel use yet.

© Jim Bond, updated Feb. 2019

Rice fields near Ubud, Bali: classical breeding ground of the mosquitoes which transmit Japanese encephalitis

Lake at dusk: Hanoi is hyper-endemic risk for Japanese encephalitis
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