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

Abstract

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.

Fig 1. wMel introgression in 12 release areas in Suva, Fiji.

A) Suva and Lami, Fiji showing the 12 release zones. B) wMel introgression. The line (left axis) represents the percent of Ae. aegypti tested that were infected with wMel Wolbachia, between June 2018 and January 2022. The bars (right axis) indicate the number of Ae. aegypti tested. Results from reporting areas where there were 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/)).

Fig 2. wMel 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/)).

Fig 3. wMel introgression in five release areas in Lautoka, Fiji.

A) Lautoka, Fiji showing the five release zones. B) wMel introgression. The line (left axis) represents the percent of Ae. aegypti tested that were infected with wMel Wolbachia, between June 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/)).

Fig 4. wMel introgression in 12 release areas in Port Vila, Vanuatu.

A) Port Vila, Vanuatu showing the 12 release areas. B) wMel introgression. The line (left axis) represents the percent of Ae. aegypti screened that were infected with wMel Wolbachia, between August 2018 and May 2021. The bars (right axis) indicate the number of Ae. aegypti tested. Data points with less than five screened 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/2016_vut_phc_admin_boundaries) and OpenMapTiles basemap layer (https://openmaptiles.org/) with CARTO light design (https://carto.com/)).

Fig 5. wMel introgression in two areas in South Tarawa, Kiribati.

A) South Tarawa, Kiribati showing the two release areas: Betio (left) and Bairiki (right). B) Introgression of wMel. The line (left axis) represents the percent of Ae. aegypti tested that were infected with wMel Wolbachia, between May 2018 and December 2019. The bars (right axis) indicate the number of Ae. aegypti tested. Data points with less than five screened mosquitos have been omitted. Shaded orange areas indicate wMel mosquito release times. Map produced in QGIS version 3.16.1 using the enumeration area boundaries freely available from the Pacific Data Hub (https://pacificdata.org/data/dataset/2010_kir_phc_admin_boundaries) and OpenMapTiles basemap layer (https://openmaptiles.org/) with CARTO light design (https://carto.com/).

Fig 6. Suspected dengue cases notified in Port Vila from January 2016 –January 2022 by (A) hospitalisation status and (B) diagnostic test result.

Blue shading indicates release period for Wolbachia (wMel)-infected Ae. aegypti. Suspected dengue cases without any laboratory diagnostic testing are included in panel A, but excluded from panel B.

Fig 7. 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.

Fig 8. Suspected chikungunya cases notified in Kiribati from January 2017 –August 2022.

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