Effectiveness ofWolbachia-infected mosquito deployments in reducing the incidence of dengue and otherAedes-borne diseases in Niterói, Brazil: a quasi-experimental study
Authors: Pinto Sofia B. , Riback Thais I. S. , Sylvestre Gabriel , Costa Guilherme , Peixoto Julia , Dias Fernando B. S. , Tanamas Stephanie K. , Simmons Cameron P. , Dufault Suzanne M. , Ryan Peter A. , O’Neill Scott L. , Muzzi Frederico C. , Kutcher Simon , Montgomery Jacqui , Green Benjamin R. , Smithyman Ruth , Eppinghaus Ana , Saraceni Valeria , Durovni Betina , Anders Katherine L. , Moreira Luciano A. 
Published: February 2021

Background

The introduction of the bacteriumWolbachia(wMel strain) intoAedes aegyptimosquitoes reduces their capacity to transmit dengue and other arboviruses. Evidence of a reduction in dengue case incidence following field releases ofwMel-infectedAe. aegyptihas been reported previously from a cluster randomised controlled trial in Indonesia, and quasi-experimental studies in Indonesia and northern Australia.

Methods

Following pilot releases in 2015 – 2016 and a period of intensive community engagement, deployments of adultwMel-infectedAe. aegyptimosquitoes were conducted in Niterói, Brazil during 2017 – 2019. Deployments were phased across four release zones, with a total area of 83 km2and a residential population of approximately 373,000. A quasi-experimental design was used to evaluate the effectiveness ofwMel 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. ThewMel 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.

Results

Three years after commencement of releases,wMel introgression into localAe. aegyptipopulations was heterogeneous throughout Niterói, 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, thewMel 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

We demonstrate thatwMelWolbachiacan be successfully introgressed intoAe. aegyptipopulations in a large and complex urban setting, and that a significant public health benefit from reduced incidence ofAedes-borne disease accrues even where the prevalence ofwMel 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 theWolbachiabiocontrol method as a multivalent intervention against dengue, chikungunya and Zika.