An outbreak of Plasmodium vivax malaria in Far North Queensland, 2002

Objective: To describe an outbreak of Plasmodium vivax malaria in Far North Queensland in 2002. Design: Epidemiological and entomological investigations; molecular analyses of the infecting parasites. Main outcome measures: Case characteristics, adult and larval mosquito counts at the outbreak location, haplotyping of parasites in blood samples from different cases determined through sequencing of AMA1 and MSP1 genes. Results: A man with imported P vivax malaria stayed at a camping ground 95 km north of Cairns in late September 2002. This led to an outbreak of P vivax malaria in 10 adults who stayed at the camping ground in October. Large numbers of Anopheles farauti sensu lato larvae were present in stagnant pools in a creek at the camping ground, and many adult mosquitoes were collected nearby. Not only had most of the infected patients been exposed to mosquitoes at night, they were also less likely than other campers to have used insect repellents appropriately (odds ratio, 0.01; P<0.001). Two different haplotypes of P vivax, only one of which was detected in the imported case, were involved in the outbreak. Conclusions: Although local transmission of malaria is rare in Far North Queensland, the risk is probably higher in the dry season (September to December). Campers need to be aware of the increased risk of mosquito-borne diseases. Sexual recombination of multiple gametocytes in mosquitoes infected by the imported case may have resulted in the two haplotypes of P vivax involved in the outbreak.