AN OUTBREAK OF JAPANESE ENCEPHALITIS IN THE TORRES STRAIT, AUSTRALIA,1995

Objectives: To determine the distribution of virus infection during an outbreak of Japanese encephalitis (JE) in the Torres Strait, and to d escribe the environmental factors facilitating the outbreak. Design: H uman and porcine serological surveys for JE virus activity throughout the Torres Strait, and mosquito and household surveys on the island of Badu. Setting: The island of Badu (where the clinical cases occurred) and the other islands of the Torres Strait, Australia, during April-M ay 1995. Results: The serological surveys identified recent JE virus i nfection among residents or domestic pigs on at least nine outer Torre s Strait islands. A JE virus, confirmed by nucleotide sequencing, was isolated from two asymptomatic Badu residents. Virus isolations and mo squito surveys implicated Culex annulirostris as the major vector invo lved in the outbreak. There was prolific Cx. annulirostris breeding in a variety of water bodies close to and within the Badu community. Ove r half (53%) of the households kept pigs in pens, and many (63%) of th e pigpens were situated near standing water; in 56% of these ''wet'' p igpens Cx. annulirostris was breeding. Conclusions: There was evidence of widespread JE virus activity throughout the outer islands of the T orres Strait. We suggest that migratory birds and/or wind-blown mosqui toes could have imported the virus into the Torres Strait from a focus of viral activity, possibly in Papua New Guinea, thereby initiating t he outbreak. A combination of environmental factors, with large number s of domestic pigs in close proximity to human dwellings and mosquito breeding sites, undoubtedly facilitated the outbreak on Badu.