Scaled deployment of Wolbachia to protect the community from dengue and other Aedes transmitted arboviruses.

Background: A number of new technologies are under development for the control of mosquito transmitted viruses, such as dengue, chikungunya and Zika that all require the release of modified mosquitoes into the environment. None of these technologies has been able to demonstrate evidence that they can be implemented at a scale beyond small pilots. Here we report the first successful citywide scaled deployment of Wolbachia in the northern Australian city of Townsville. Methods: The wMel strain of Wolbachia was backcrossed into a local Aedes aegypti genotype and mass reared mosquitoes were deployed as eggs using mosquito release containers (MRCs). In initial stages these releases were undertaken by program staff but in later stages this was replaced by direct community release including the development of a school program that saw children undertake releases. Mosquito monitoring was undertaken with Biogents Sentinel (BGS) traps and individual mosquitoes were screened for the presence of Wolbachia with a Taqman qPCR or LAMP diagnostic assay. Dengue case notifications from Queensland Health Communicable Disease Branch were used to track dengue cases in the city before and after release. Results: Wolbachia was successfully established into local Ae. aegypti mosquitoes across 66 km 2 in four stages over 28 months with full community support.  A feature of the program was the development of a scaled approach to community engagement. Wolbachia frequencies have remained stable since deployment and to date no local dengue transmission has been confirmed in any area of Townsville after Wolbachia has established, despite local transmission events every year for the prior 13 years and an epidemiological context of increasing imported cases. Conclusion: Deployment of Wolbachia into Ae. aegypti populations can be readily scaled to areas of ~60km 2 quickly and cost effectively and appears in this context to be effective at stopping local dengue transmission

GraphData_Figure 3.docx

Data underlying Figure 3 of O'Neill et al 2018 Gates Open Researc

Successful introgression of wMel Wolbachia into Aedes aegypti populations in Fiji, Vanuatu and Kiribati.

Pacific Island countries have experienced periodic dengue, chikungunya and Zika outbreaks for decades. The prevention and control of these mosquito-borne diseases rely heavily on control of Aedes aegypti mosquitoes, which in most settings are the primary vector. Introgression of the intracellular bacterium Wolbachia pipientis (wMel strain) into Ae. aegypti populations reduces their vector competence and consequently lowers dengue incidence in the human population. Here we describe successful area-wide deployments of wMel-infected Ae. aegypti in Suva, Lautoka, Nadi (Fiji), Port Vila (Vanuatu) and South Tarawa (Kiribati). With community support, weekly releases of wMel-infected Ae. aegypti mosquitoes for between 2 to 5 months resulted in wMel introgression in nearly all locations. Long term monitoring confirmed a high, self-sustaining prevalence of wMel infecting mosquitoes in almost all deployment areas. Measurement of public health outcomes were disrupted by the Covid19 pandemic but are expected to emerge in the coming years

DENV Prevalence in <i>Wolbachia</i>-infected Mosquitoes.

Pacific Island countries have experienced periodic dengue, chikungunya and Zika outbreaks for decades. The prevention and control of these mosquito-borne diseases rely heavily on control of Aedes aegypti mosquitoes, which in most settings are the primary vector. Introgression of the intracellular bacterium Wolbachia pipientis (wMel strain) into Ae. aegypti populations reduces their vector competence and consequently lowers dengue incidence in the human population. Here we describe successful area-wide deployments of wMel-infected Ae. aegypti in Suva, Lautoka, Nadi (Fiji), Port Vila (Vanuatu) and South Tarawa (Kiribati). With community support, weekly releases of wMel-infected Ae. aegypti mosquitoes for between 2 to 5 months resulted in wMel introgression in nearly all locations. Long term monitoring confirmed a high, self-sustaining prevalence of wMel infecting mosquitoes in almost all deployment areas. Measurement of public health outcomes were disrupted by the Covid19 pandemic but are expected to emerge in the coming years.</div

<i>Wolbachia</i>-mediated reduction in DENV genome copy number per mosquito.

All mosquitoes were aged for 6–7 days prior to intrathoracic injection with DENV. Fifty mosquitoes were used for each data point but some died prior to testing (S3 Table). DENV copy number was determined 7 days post injection using qRT-PCR. All wMel Ae. aegypti lines had a significant reduction in DENV viral RNA concentration (Wilcoxon rank-sum est). A) Fiji release strain, Fij-wMel, and wild-derived control, Fij-WT,vector competence. B) Vanuatu release strain, Van-wMel, and wild-derived control, Van-WT, vector competence. C) Kiribati release strain, Kir-wMel, and wild-derived control, Kir-WT, vector competence. D) Australian Cairns strain, Aus-wMel, and tetracycline cured control, Aus-TET, vector competence. Data are shown as the median DENV copies per mosquito (thick line) ± interquartile ranges (box), extended by the whiskers indicating 1.5× the interquartile range, with dots indicating outliers. Individual data points are included as smaller partially opaque points. Data from uninfected mosquitoes are not included in the median estimates (S3 Table). (TIFF)</p

Public Acceptance Surveys.

Outcome of community surveys taken at baseline (prior to engagement activity) and pre-release (prior to deployment of Wolbachia-infected mosquitoes). Awareness was determined by asking participants if they had heard of the World Mosquito Program. Acceptance was determined by asking participants if, once it was explained to them, they approved of releasing mosquitoes with good bacteria to reduce dengue.</p

Release & monitoring of <i>w</i>Mel-infected <i>Ae</i>. <i>aegypti</i> within 12 areas of Port Vila, Vanuatu.

Each release area was divided into a grid with 100 x 100 meter squares. Grid squares lacking mosquito releases were omitted. Release gradient was determined by using GPS coordinates of each release event and assigning the number of wMel-infected mosquitos to a corresponding grid square. Monitoring numbers were determined in the same way. Map produced in QGIS version 3.16.1 using boundaries aggregated from the enumeration area boundaries freely available from the Pacific Data Hub (https://pacificdata.org/data/dataset/2016_vut_phc_admin_boundaries) and OpenMapTiles basemap layer (https://openmaptiles.org/) with CARTO light design (https://carto.com/)). (PNG)</p

<i>w</i>Mel introgression in six release areas in Nadi, Fiji.

A) Nadi, Fiji showing the six release zones. B) wMel introgression. The line (left axis) represents the percent of Ae. aegypti tested that were infected with wMel Wolbachia, between July 2019 and January 2022. The bars (right axis) indicate the number of Ae. aegypti tested. Data points with less than five tested mosquitos have been omitted. Shaded orange areas indicate wMel mosquito release times. Map produced in QGIS version 3.16.1 using boundaries aggregated from the enumeration area boundaries freely available from the Pacific Data Hub (https://pacificdata.org/data/dataset/2007_fji_phc_admin_boundaries) and OpenMapTiles basemap layer (https://openmaptiles.org/) with CARTO light design (https://carto.com/)).</p

Suspected dengue cases notified in Kiribati from January 2009 –August 2022 by diagnostic test result.

Blue shading indicates release period for Wolbachia (wMel)-infected Ae. aegypti.</p