Sydney University Department of Medical Entomology Westmead Hospital
Japanese Encephalitis virus
Overview Natural History
Symptoms Laboratory Diagnosis
Treatment Prevention
Further Reading

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Japanese encephalitis virus is a mosquito-borne virus which is potentially fatal in humans. It is spread throughout eastern Asia, including India, Japan, China and southeast Asia. The virus made its appearance in Australia for the first time in 1995, when three residents of Badu Island in the Torres Strait developed clinical disease and two died. Antibodies in humans and pigs were demonstrated on other islands, and JE was isolated from Culex annulirostris collected on Badu Island. In late 1995, 93% of humans in the region of activity were vaccinated.

Serological evidence that transmission had occurred in pigs in 1996 and 1997 followed, as did evidence that JE virus has been in PNG for eight or more years and has spilt over into the Torres Strait islands in the past four years: in 1995 into humans, in 1996 and 1997 into pigs, and in 1998 into humans and pigs. In March 1998, a boy from the island of Badu was hospitalised with JE infection, indicating renewed activity in the region; the boy came from a religious group that had refused vaccination during the 1995 campaign. Later the same month, a professional fisherman was infected while in the Mitchell River area on the western side of Cape York Peninsula; this was the first case of JE infection acquired on the mainland of Australia (seropositive pigs have also been detected in the Mitchell river area). Both patients recovered.

Natural History

The natural cycle of Japanese encephalitis (JE) virus in Asia involves water birds and Culex mosquitoes, particularly Cx. tritaeniorhynchus, with pigs being also involved as an amplifying host and providing a link to humans through  their proximity to housing. In the Torres Strait outbreak, Cx. annulirostris was found to be infected and is presumed to be the principal vector. If JE virus was to continue activity in the region, it is likely that it could become established on the mainland further south, and could present a major problem in areas where Cx. annulirostris is abundant.

Symptoms, Diagnosis, Treatment

Symptoms of infection are similar to those described for Murray Valley Encephalitis (MVE) virus, and JE virus has a comparable mortality rate of 20-30%. Likewise, the diagnosis and treatment are essentially the same, although specific JE virus antibodies are tested for in the blood tests.


A vaccine is available to prevent infection and available through clinics that specialise in travel medicine. Individuals who travel to Asian countries should consult a travel medicine clinic on the need for vaccination. General mosquito avoidance measure as per MVE are also advisable, including the use of insecticide impregnated nets when sleeping in rural areas.

Further Reading

Burke, D.S. and Leake, C.J. (1988). Japanese Encephalitis. in Monath, T. (ed). The Arboviruses: Epidemiology and Ecology, Volume III. CRC Press, Florida, pg: 63-92.

Assoc. Prof. Richard C. Russell and Stephen L. Doggett


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