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DHS information: www.dhs.vic.gov.au/phb/
Overseas information: http://www.cdc.gov/travel/jenceph.htm

Japanese Encephalitis

Japanese B encephalitis, an uncommon but serious infection, is endemic throughout most of the Far East and South East Asia. Symptoms include headache, reduced consciousness, spacticity and fits.The incubation period is between 5 to 15 days

The case fatality rate in epidemics is 10-50%, and about half the survivors are left with neurological damage. Children and the elderly have a significant higher incidence of complications. The causal virus is transmitted by rice field breeding mosquitoes. Pigs, horses and wild birds are the amplifier hosts. The proximity of pigs to humans increases the chance of transmission.

Immunisation in humans is the only practicable way to prevent disease, and vaccine is available. Protective efficacy is 95%. Some authorities claim that the vaccine provides some protection against Dengue but evidence of this is unreliable.

More recently Japanese Encephalitis has become established in Papua New Guinea and the Torres Strait Islands with sporadic cases  in Northern Australia

Distribution of Japanese B encephalitis:
1 . Epidemic areas

  • annual outbreaks of 4 - 5 months at the end of the wet season in late Summer and Autumn (April to November) with peak transmission in May-June.
  • in temperate regions and northern part of tropical zones in: Bangladesh ,Japan, Nepal, Burma (northern), Kampuchea, Thailand (north-Chiang Mai area), Korea, Vietnam, China (except Xinzang/Tibet, Xinjiang/Sinklang and Qinghai), India (northern), Laos, eastern areas of Russia.

2. Endemic areas

  • Sporadic cases occur throughout the year.
  • in tropical areas of: Indonesia, Philippines, South India , Laos, Singapore, Taiwan, Malaysia, Sri Lanka, south Thailand, India (in particular West Bengal, Uttar Pradesh, Andhra Pradesh, Bihar, Karnataka and Assam), lowlands of Nepal.
  • In subtropical and tropical areas, risk is present throughout the year, but is accentuated during rainy season and early dry season when mosquito populations are higher.

3. Indications for Use
The old
vaccine availability was restricted in 1991 due to a high incidence of allergic reactions, but it is now believed that these related to certain batches of the vaccine. The new vaccines are much safer.

Vaccination is recommended for travellers spending more than 4 weeks in rural areas of Asia, particularly if travel is during the wet season, and/or there is considerable outdoor activity and/or the standard of accommodation is suboptimal. Vaccination is also recommended for expatriates spending a year or more in Asia (excluding Singapore) even in urban areas.
p 47. Australian Immunisation Handbook, 8th Edition 9/2003Part 3.12, 'Japanese encephalitis').

4. New Vaccines

(a) JESPECT (called 'Ixiaro' overseas) - approved product information

  • registered for children 18 years old and above
  • 2 injections 28 days apart (currently approx $130/dose)

(B) IMOJEV (licensed in august 2010) - a live-attenuated virus based on Yellow Fever vaccine

  • registered as single dose for children 12 months old and above
  • 93% seroconversion after 14 days (88% seropositive at 48 months compared to 28% with JE-VAX)
  • Boosters

Dosage of old vaccine JE-VAX

  • 3 doses of vaccine given subcutaneously at 0, 7 or 14, and 30 days.
  • 1ml for adults and children over 3 and 0.5ml for 1 - 3 years.
  • Confers 99% immunity for 3 dose regeime and boosters every 3 years.
  • Vaccine is quite reactogenic with serious reactions in 0.6% of vaccinees.
  • Wheeze,urticaria and erythema multiforme can occur up to 10 days after vaccination.
  • Persons with a past history of urticaria appear to have a greater risk of reactions.

NB. 9000 doses of vaccine were given in a recent immunisation campaign (1995/96) in the torres straight islands without any serious reactions.

Disease outbreaks: http://www.who.int/emc/outbreak_news/index.html

Information mostly taken from: "International Travel and Health" (WHO year book - internet only)
Australian Immunisation Handbook, 8th Edition - 9/2003 - Part1 - Part 2 & Part 3 (large pdf files)
Centre for Disease Control, USA -  www.cdc.gov/travel Travel Health Seminar Oct 96, June 97,Feb 98, March 99, May 2000, August 2002 & March 2005 - Victorian Medical Postgraduate Foundation.
Manual of Travel Medicine, Melbourne, Oct 2004. Updated 3rd edition 2011.  Additional references & disclaimer.

Last edited: 29 July, 2012

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North East Valley Division General Practice, Victoria, Australia, Disclaimer 
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