Japanese Encephalitis


Dr Tu Khai Huynh – TMA Member Ipswich

Japanese Encephalitis (JE) occurs in practically all Asian countries and is also now considered endemic in the Torres Strait region and Papua New Guinea. The incidence of JE in humans varies by season, usually coinciding with the rains and is mainly passed through the bite of the Culex mosquito.

Country Peak transmission


Korea, Japan May to September
Temperate South East Asia (Thailand,Vietnam, Cambodia) April to October
Nepal, Northern India September to December
Malaysia, Indonesia and Philippines and tropical regions of South East Asia All year round
Humans are infected by the virus (JEV) when living in close proximity its natural hosts (pigs and wading birds). This usually occurs in rural areas where there is breeding of the vectors in flooded rice fields. Nearly 3 billion people are believed to be at risk for JE virus infection and approximately 20,000 clinical cases with 6,000 deaths are reported annually.

Infection is characterized by sudden onset of fever, chills, muscle aches, and confusion. It is recognised, however, that most infections are asymptomatic; published estimates of the symptomatic to asymptomatic infection ratio vary in different populations from 1:25 to 1:1000.. The case fatality rate ranges from 5-30% but approximately 30-50 % of the surviving patients have permanent brain damage and complete recovery occurs in only one-third of patients.

 Culex mosquito – Females bite usually during the day time but peak at dawn and at dusk. All travellers to Asia (and other tropical regions) must be fully aware of the need to take appropriate measures to avoid mosquito bites, such as effective insect repellent and appropriate clothing.
Risk for travellers

The risk to short term travellers to Asia is very low, particularly if they are only visiting urban areas, with overall estimates of one case per million travellers. The risk becomes greater for persons who intend to live or travel in risk areas for long periods of time, and have rural trips during transmission seasons. Certain activities may increase the risk such as fieldwork, camping, or cycling in rural areas. The risk amongst rural travellers has been estimated to be in the range of 1 case per 5,000 travellers to 1 per 20,000 per week.

Treatment

There is no specific treatment, but rather supportive management.

Prevention

Apart from personal protective measures to avoid being bitten, vaccination of humans is the most effective means of preventing JE. Two vaccines are available for use in Australia:

  1. JEspect is an inactivated vaccine given by 2 vaccinations 4 weeks apart; and is licenced for use in travellers from 18 years onwards.
  2. IMOJEV is a live weakened strain of JEV given as a single dose for travellers over 12 months of age.

JE vaccination is recommended for:

  1. Travellers (≥12 months of age) spending 1 month or more in rural areas of high-risk countries in Asia and Papua New Guinea (see 4.8.3 Epidemiology above); however, should be considered for shorter-term travellers, particularly if the travel is during the wet season, or anticipated to be repeated, and/or there is considerable outdoor activity, and/or the accommodation is not mosquito-proof.
  2. All other travellers spending a year or more in Asia (except Singapore), even if much of the stay is in urban areas.

Please consult your travel doctor for timely advice about Japanese encephalitis if you are going to Asia or PNG, especially those times listed above, and especially if your travel will involve a lot of rural activity.

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