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Japanese Encephalitis (JE)

JE occurs in a number of countries in Asia and occasionally in Northern Queensland Australia, and East Rusia.

The overall incidence of JE reported among people from nonendemic countries traveling to Asia is 1 case per 1 million travelers. However, expatriates and travelers staying for prolonged periods in rural areas with active JEV transmission are likely at similar risk as the susceptible resident population (0.1-2 cases per 100,000 persons per week).

Causative agent: Japanese encephalitis (JE), which is a Flavivirus

Transmission: The virus is transmitted to humans via the bite of infected various mosquitoes of the genus Culex (Culex tritaeniorhynchus and gelidus). It infects pigs and various wild birds as well as humans. Mosquitoes become infective after feeding on viraemic pigs or birds (reservoir). Humans are a dead-end host in the JE transmission cycle.

Incubation period: 4 – 16 days

Sign & Symptoms

  • Most infections are asymptomatic (95.5%).
  • Acute encephalitis is the most commonly recognized clinical manifestation of JE infection. Milder forms of disease such as aseptic meningitis or undeffentiated febrile illness can be also accur.
  • Mild infections are characterized by febrile headache or aseptic meningitis.
  • Severe cases have a rapid onset and progression with headache, high fever and meningeal signs such as fits, nausea and vomiting.
  • Seizures develop in 66% of cases, most often in children.
  • Approximately 50% of severe clinical cases have a fatal outcome
  • Hepatosplenomegaly, pneumonia and chronic carriers


Permanent neurological sequelae are common among survivors eg. Paralysis and body weaknesess and brain death.


Symptomatic treatment: Advise rest, drink plenty of fluids and take regular painkillers (e.g. Paracetamol or Ibuprofen) to relieve symptoms of fever and aching.

No specific treatment. No drugs for treating JE infection are available

Prevention & Precautions

  • Avoiding mosquito bites is important
  • The vaccine should be considered for all travelers to rural endemic zones if they intend to stay there for at least 2 weeks.
  • The dose and schedule of the vaccine depends on the type of vaccine. Please see your doctor for further advise

Before departure: At least two (2) doses before departure


  • Minimize exposure to bites by modifying activities to avoid exposure to vector bites.
  • Avoid mosquito bite by applying mosquito repellent to exposed skin. When using sunscreen or lotions, apply repellants last. Reapply whenever sweat or water has removed it. Active ingredient in a repellent repels but does not kill insects. Repellent that contains DEET (N, N-diethylmetatoluamide) is most reliable and long-lasting type (35% DEET provides protection for 12 hours). DEET formulations as high as 50% are recommended for both adults (including pregnant women) and children >2 months of age. It is toxic when ingested and may cause skin irritation. Permethrin is highly effective both as an insecticide and as a repellent. There is little potential for toxicity from Permethrin-treated clothing.
  • Use long sleeved clothes and long pant. Avoid wearing dark colours (attract mosquitoes).
  • Close windows or shutters at night when indoors. Use pyrethrum insecticide spray (aerosol insecticides), pyrethroid coils or insecticide impregnated tablets in evening before sleep.
  • Avoid strong perfumes, hair sprays or after-shaves (attract mosquitoes)!
  • Use air-conditioning or good mosquito net especially treated with Permethrin.

References organisation/ support

  • International Travel & Health, WHO 2006
  • Control of Communicable Diseases Manual, 18th Edition by David L. Heymann, MD, Editor, 2004
  • http://travelhealth.co.uk/


Last reviewed : 28 August 2020
Writer : Dr. Fuad Hashim
Reviewer : Dr. Nor Faizah bt. Ghazali