Effectiveness of Wolbachia-infected mosquito deployments in reducing the incidence of dengue and other Aedes-borne diseases in Niteroi, Brazil: A quasi-experimental study

Background The introduction of the bacterium Wolbachia (wMel strain) into Aedes aegypti mosquitoes reduces their capacity to transmit dengue and other arboviruses. Evidence of a reduction in dengue case incidence following field releases of wMel-infected Ae. aegypti has been reported previously from a cluster randomised controlled trial in Indonesia, and quasi-experimental studies in Indonesia and northern Australia. Methodology/Principal findings Following pilot releases in 2015-2016 and a period of intensive community engagement, deployments of adult wMel-infected Ae. aegypti mosquitoes were conducted in Niteroi, Brazil during 2017-2019. Deployments were phased across four release zones, with a total area of 83 km(2) and a residential population of approximately 373,000. A quasi-experimental design was used to evaluate the effectiveness of wMel deployments in reducing dengue, chikungunya and Zika incidence. An untreated control zone was pre-defined, which was comparable to the intervention area in historical dengue trends. The wMel intervention effect was estimated by controlled interrupted time series analysis of monthly dengue, chikungunya and Zika case notifications to the public health surveillance system before, during and after releases, from release zones and the control zone. Three years after commencement of releases, wMel introgression into local Ae. aegypti populations was heterogeneous throughout Niteroi, reaching a high prevalence (>80%) in the earliest release zone, and more moderate levels (prevalence 40-70%) elsewhere. Despite this spatial heterogeneity in entomological outcomes, the wMel intervention was associated with a 69% reduction in dengue incidence (95% confidence interval 54%, 79%), a 56% reduction in chikungunya incidence (95%CI 16%, 77%) and a 37% reduction in Zika incidence (95%CI 1%, 60%), in the aggregate release area compared with the pre-defined control area. This significant intervention effect on dengue was replicated across all four release zones, and in three of four zones for chikungunya, though not in individual release zones for Zika. Conclusions/Significance We demonstrate that wMel Wolbachia can be successfully introgressed into Ae. aegypti populations in a large and complex urban setting, and that a significant public health benefit from reduced incidence of Aedes-borne disease accrues even where the prevalence of wMel in local mosquito populations is moderate and spatially heterogeneous. These findings are consistent with the results of randomised and non-randomised field trials in Indonesia and northern Australia, and are supportive of the Wolbachia biocontrol method as a multivalent intervention against dengue, chikungunya and Zika. Author summary The Aedes aegypti mosquito transmits dengue, chikungunya, Zika and other viral diseases between humans. Previous research has shown that when a symbiotic bacterium called Wolbachia-which exists naturally in many other insect species-is introduced into Ae. aegypti mosquitoes it makes them less able to transmit dengue and other viruses, and is passed from generation to generation via mosquito eggs. The authors report that after releasing Wolbachia-carrying Ae. aegypti in the Brazilian city of Niteroi for periods during 2017 to 2019, between 33% and 90% of the Ae. aegypti mosquito population in four release zones were infected with Wolbachia by March 2020. The authors used controlled interrupted time series analysis to show that Wolbachia deployments were associated with a 69% reduction in dengue cases notified to the public health authorities, compared to a control area of Niteroi that did not receive Wolbachia releases. Chikungunya and Zika case incidence was also significantly lower in the Wolbachia release areas. These results support previous findings from Indonesia and Australia, and show that Wolbachia mosquito releases are an effective and sustainable method for controlling dengue and other diseases spread by Ae. aegypti mosquitoes, even in large and complex urban environments.

Automated summary

The introduction of the wMel strain of the bacterium Wolbachia into Aedes aegypti mosquitoes has been shown to significantly reduce the transmission of dengue, chikungunya, and Zika viruses. In a study conducted in Niteroi, Brazil, it was found that after three years of releases, there was a significant reduction in dengue, chikungunya, and Zika incidence in areas where the wMel-infected mosquitoes were deployed. This approach proved effective in reducing Aedes-borne diseases, even in environments with moderate and spatially heterogeneous prevalence of the wMel bacteria.