An outbreak of Barmah Forest virus disease in the south-west of Western Australia.

OBJECTIVES

To describe the first reported outbreak of Barmah Forest (BF) virus disease in the south-west of Western Australia.

DESIGN

Case series correlated with results of arbovirus surveillance. All patients with clinically suspected Ross River (RR) virus infection were serologically tested for antibodies to BF and RR viruses. Home address and date of presentation of patients with serologically confirmed recent infection were recorded. Mosquitoes collected from the districts before and during the BF virus outbreak were identified to species level and tested for virus.

RESULTS

Twenty-two cases of BF disease were reported from the region between August 1992 and March 1994. Most occurred in the Peel region in the spring and early summer of 1993. Eighteen isolates of BF virus were obtained from three different species of mosquito trapped between January and October 1993. Fifteen were from mosquitoes in the Peel region and a single isolate was from the Perth metropolitan area. No isolates were obtained from the region before 1993. RR virus was not isolated from mosquitoes trapped in the region during the BF virus outbreak.

CONCLUSIONS

Most BF infections were acquired in the Peel region during spring and early summer of 1993. Aedes camptorhynchus mosquitoes were probably the main vectors. The lack of isolations from mosquitoes before 1993 suggests that the virus may have only recently been introduced (or reintroduced) to the region. It was transmitted under conditions that were apparently not conducive to transmission of RR virus.