Limited Dengue Virus Replication in Field-Collected Aedes aegypti Mosquitoes Infected with Wolbachia

Introduction Dengue is one of the most widespread mosquito-borne diseases in the world. The causative agent, dengue virus (DENV), is primarily transmitted by the mosquito Aedes aegypti, a species that has proved difficult to control using conventional methods. The discovery that A. aegypti transinfected with the wMel strain of Wolbachia showed limited DENV replication led to trial field releases of these mosquitoes in Cairns, Australia as a biocontrol strategy for the virus. Methodology/Principal Findings Field collected wMel mosquitoes that were challenged with three DENV serotypes displayed limited rates of body infection, viral replication and dissemination to the head compared to uninfected controls. Rates of dengue infection, replication and dissemination in field wMel mosquitoes were similar to those observed in the original transinfected wMel line that had been maintained in the laboratory. We found that wMel was distributed in similar body tissues in field mosquitoes as in laboratory ones, but, at seven days following blood-feeding, wMel densities increased to a greater extent in field mosquitoes. Conclusions/Significance Our results indicate that virus-blocking is likely to persist in Wolbachia-infected mosquitoes after their release and establishment in wild populations, suggesting that Wolbachia biocontrol may be a successful strategy for reducing dengue transmission in the field. Author Summary Almost half of the world's population is at risk of contracting dengue virus, particularly in the tropics and sub-tropics. The virus is transmitted by the mosquito Aedes aegypti, a cosmopolitan species that has proved difficult to control using traditional methods. A new biocontrol strategy has been developed involving the release of mosquitoes infected with Wolbachia bacteria. Mosquitoes with the wMel strain of Wolbachia show dramatically reduced replication and transmission of dengue virus in laboratory trials. Although promising, the utility of Wolbachia biocontrol depends on field wMel-infected mosquitoes retaining the phenotype of reduced viral replication. Mosquitoes with wMel were released in the field in Cairns, Australia in early 2011. We provide evidence that, one year later, field collected wMel mosquitoes showed reduced dengue virus replication in the body and limited dissemination to the head compared to controls. Wolbachia numbers in mosquitoes increased following blood meals, which may further decrease viral replication if the insects feed frequently. Our results indicate that Wolbachia-mediated dengue interference is sustained in field populations and shows no sign of attenuation after one year of deployment.