Establishment of wMel Wolbachia in Aedes aegypti mosquitoes and reduction of local dengue transmission in Cairns and surrounding locations in northern Queensland, Australia

Abstract

<ns4:p><ns4:bold>Background: </ns4:bold>The <ns4:italic>w</ns4:italic>Mel strain of<ns4:italic> Wolbachia</ns4:italic> has been successfully introduced into <ns4:italic>Aedes aegypti</ns4:italic> mosquitoes and subsequently shown in laboratory studies to reduce transmission of a range of viruses including dengue, Zika, chikungunya, yellow fever, and Mayaro viruses that cause human disease. Here we report the entomological and epidemiological outcomes of staged deployment of <ns4:italic>Wolbachia</ns4:italic> across nearly all significant dengue transmission risk areas in Australia.</ns4:p><ns4:p> <ns4:bold>Methods: </ns4:bold>The <ns4:italic>w</ns4:italic>Mel strain of <ns4:italic>Wolbachia</ns4:italic> was backcrossed into the local <ns4:italic>Aedes aegypti</ns4:italic> genotype (Cairns and Townsville backgrounds) and mosquitoes were released in the field by staff or via community assisted methods. Mosquito monitoring was undertaken and mosquitoes were screened for the presence of <ns4:italic>Wolbachia</ns4:italic>. Dengue case notifications were used to track dengue incidence in each location before and after releases.</ns4:p><ns4:p> <ns4:bold>Results: </ns4:bold>Empirical analyses of the <ns4:italic>Wolbachia</ns4:italic> mosquito releases, including data on the density, frequency and duration of <ns4:italic>Wolbachia</ns4:italic> mosquito releases, indicate that <ns4:italic>Wolbachia</ns4:italic> can be readily established in local mosquito populations, using a variety of deployment options and over short release durations (mean release period 11 weeks, range 2-22 weeks). Importantly, <ns4:italic>Wolbachia</ns4:italic> frequencies have remained stable in mosquito populations since releases for up to 8 years. Analysis of dengue case notifications data demonstrates near-elimination of local dengue transmission for the past five years in locations where <ns4:italic>Wolbachia</ns4:italic> has been established. The regression model estimate of <ns4:italic>Wolbachia </ns4:italic>intervention effect from interrupted time series analyses of case notifications data prior to and after releases, indicated a 96% reduction in dengue incidence in <ns4:italic>Wolbachia </ns4:italic>treated populations (95% confidence interval: 84 – 99%).</ns4:p><ns4:p> <ns4:bold>Conclusion: </ns4:bold>Deployment of the <ns4:italic>w</ns4:italic>Mel strain of <ns4:italic>Wolbachia</ns4:italic> into local <ns4:italic>Ae. aegypti</ns4:italic> populations across the Australian regional cities of Cairns and most smaller regional communities with a past history of dengue has resulted in the reduction of local dengue transmission across all deployment areas.</ns4:p>