Entomological Investigations of an Outbreak of Japanese Encephalitis Virus in the Torres Strait, Australia, in 1998
Journal of medical entomology
Japanese encephalitis (JE) virus Þrst appeared in Australia in 1995, when three clinical cases (two fatal) were diagnosed in residents on Badu Island in the Torres Strait, northern Queensland. More recently, two conÞrmed human JE cases were reported in the Torres Strait Islands and Cape York Peninsula, in northern Queensland in 1998. Shortly after JE virus activity was detected in humans and sentinel pigs on Badu Island in 1998, adult mosquitoes were collected using CO 2 and octenol-baited CDC
... ight traps; 43 isolates of JE virus were recovered. Although Culex sitiens group mosquitoes yielded the majority of JE isolates (42) , one isolate was also obtained from Ochlerotatus vigilax (Skuse). Four isolates of Ross River virus and nine isolates of Sindbis (SIN) virus were also recovered from members of the Culex sitiens group collected on Badu Island in 1998. In addition, 3,240 mosquitoes were speciated and pooled after being anesthetized with triethylamine (TEA). There was no signiÞcant difference in the minimum infection rate of mosquitoes anesthetized with TEA compared with those sorted on refrigerated tables (2.8 and 1.6 per 1,000 mosquitoes, respectively). Nucleotide analysis of the premembrane region and an overlapping region of the Þfth nonstructural protein and 3Ј untranslated regions of representative 1998 Badu Island isolates of JE virus revealed they were identical to each other. Between 99.1% and 100% identity was observed between 1995 and 1998 isolates of JE from Badu Island, as well as isolates of JE from mosquitoes collected in Papua New Guinea (PNG) in 1997 and 1998. This suggests that the New Guinea mainland is the likely source of incursions of JE virus in Australia.