Japanese Encephalitis

What is Japanese Encephalitis?

Japanese encephalitis (JE) is viral infection in the brain caused by flavivirus. The virus is found in pigs and birds and is transferred to mosquitoes when they bite the infected animal.

There is currently no cure for JE therefore it is vital to undergo assessment before travel to determine whether vaccination is required and to ensure effective bite prevention precautions are taken. It is found mainly in Asia.1

The following is a summary about the disease. For further details speak to your local pharmacist or GP.

How is JE spread?

JE virus is spread to humans via the bite of an infected Culex spp. mosquito. These mosquitoes feed predominantly during the night, between dusk and dawn.1

In which countries is JE found in?

JE is predominant in rural parts of Asia and the Pacific Rim where rice cultivation and pig farming are common.


The spread of JE can be found here.2

Factors favouring disease in these areas include:

  • The presence of the Culex spp. Mosquitoes
  • Mosquito habitats (such as rice-growing fields, swamps and marshes)
  • Suitable environmental conditions necessary for the mosquito breeding cycle (rainfall, humidity, tropical temperatures)
  • Presence of the amplifying hosts (pigs and birds).1

What are the signs and symptoms of JE?

Most cases of JE are asymptomatic or present with non-specific flu-like symptoms. Approximately 1 in 250 people develop more severe symptoms.

The incubation period is 5-15 days, and initial symptoms include:

  • Fever
  • Headache
  • Nausea
  • Stiff neck
  • Seizures
  • Tremors
  • Muscle weakness leading to paralysis1

What are the complications of JE?

Symptoms progress to:

  • Meningoencephalitis with convulsions and altered consciousness
  • Pneumonia
  • Urinary tract infections


Neurological complications may not fully resolve and survivors are left with significant neurological problems.

Of those who develop encephalitis, approximately 30% die.1

How is JE treated?

At present, there is no available cure for JE.

Treatment is supportive with severe cases requiring hospital treatment.  Long-term care for neurological complications may be needed.1

What advice is there for those travelling to high risk countries?

The risk of JE to most travellers to Asia is very low, especially for short-term stay in urban areas.  The risk varies on the basis of:

  • Destination (higher risk in rural areas)
  • Duration (short trips (usually less than a month) especially if only travelling to urban areas, are considered lower risk.)
  • Season (Monsoon time when numbers of mosquitoes are higher increase risk)
  • Activities (outdoor activities such as fieldwork, camping, or cycling can increase the risk)

A JE vaccine is available and is recommended for those intending to stay for long periods and whose planned activities will increase their risk.1

The risk of acquiring JE can be reduced by insect bite avoidance methods such as:

  • Applying a good-quality insect repellent (such as DEET) to exposed areas of skin
  • Avoiding mosquito bites, particularly between the hours of dusk and dawn
  • Use mosquito nets impregnated with an insecticide
  • Spray insecticide in the early evening to kill any mosquitoes in the room
  • Cover up with long-sleeved tops, trousers and socks – especially in the evening
  • Wear loose-fitting clothes as mosquitoes can bite through skin-tight clothing3

When to consider vaccination

The vaccination is available privately through travel clinics and  travellers should undergo a careful risk assessment which considers the itinerary, duration of stay, season of travel and planned activities. Country specific recommendations can be found here.4

JE vaccine is recommended for travellers:

  • Intending to stay in an area where JE is known to occur
  • Staying a month or longer in the risk area, especially rural areas.
  • Spending time in rice fields (where the mosquito vector breeds) or close to pig farms – regardless of length of stay
  • Laboratory staff with the potential to be exposed to JE1


The JE vaccination is suitable for adults and children aged 2 months and over.

The vaccine is given as an injection of 2 doses. The second dose is usually given 28 days after the first dose to obtain full protection. An accelerated schedule is available for adults aged 18-65 years, where the second dose is given after 7 days following the first dose.

With both schedules, the dose of the second vaccine should be completed at least 7 days before travelling to an area where there is a risk of JE.

For travellers who continue to be at risk of infection, a first booster dose of the vaccine should be given 12 to 24 months after the first dose. A second booster can be given after 10 years to those who remain at risk.5


This information is taken from trusted third party websites, NaTHNaC (Travel Health Pro) and EMIS (Patient info) and use of all information has been licenced under the Open Government Licence http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/.

Although the materials are being used/replicated under the provisions of the Open Government Licence this in no way represents endorsement of Traveljab.co.uk by NaTHNaC, Emis, Public Health England, the NHS or the Department of Health and Social Care.

  1. Travel Health Pro (NaTHNaC): Japanese Encephalitis
  2. WHO map: Japanese encephalitis, countries or areas at risk
  3. NHS: Japanese Encephalitis
  4. Travel Health Pro (NaTHNaC): Country information
  5. The Green Book: Chapter 20 – Japanese encephalitis