Isolation of Japanese encephalitis virus from Culex annulirostris in Australia

Mosquitoes were collected using CO2 and octenol-baited light traps during an outbreak of Japanese encephalitis (JE) on Badu Island in the Torres Strait, Australia in April 1995. A total of 13,300 mosquitoes comprising 12 species were processed for virus isolation. Eight isolates of JE virus were obtained from Culex annulirostris, with a carriage rate of 2.97:1,000; this mosquito also yielded one Sindbis virus isolate. A reverse transcriptase-polymerase chain reaction was used to sequence the JE viruses, which were compared with published sequences. The eight isolates were 90% homologous with known JE strains but only 68% homologous with other flaviviruses. Among the isolates, 99% homology was obtained, suggesting a common point of origin.