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Japanese Encephalitis (JE)

Introduction

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 JEV 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

Complication

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

Treatment

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 preventing JEV infection are available

Prevention & Precautions

The vaccine should be considered for all travelers to rural endemic zones if they intend to stay there for at least 2 weeks.

Type of vaccine: Inactivated mouse-brain-derived

Number of doses: Standard 3 doses schedule or reduced 2 dose schedule , subcutaneous

Schedule: 3 doses at days 0, 7 and 28 OR 2 doses given 1 – 4 weeks apart (1.0ml for adults, 0.5ml for children)

Booster: After 1 year and then 3 yearly

Contraindications: Hypersensitivity to previous dose or to the vaccine preservative thiomersal

Adverse reactions: Occasional mild local or systemic reaction, occasional severe reaction with generalized urticaria, hypotension and collapse

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

Recommended for: Travellers over 1 year of age and staying in endemic rural areas for more than 2 weeks

Special precautions: Avoiding mosquito bites is as important as being immunized.

Precautions

  • 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 : 26 April 2012
Writer : Dr. Fuad Hashim
Reviewer : Dato’ Dr. Hj. Md Hanip b. Rafia