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

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.</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

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

Pre-release Mosquito Strain Health Checks.

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>w</i>Mel 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/).</p

Total (A) and laboratory-confirmed (B) dengue cases notified in Kiribati from January 2017 –August 2022 by recorded location of residence.

Cases with an ‘address’ location recorded were classified either as resident in the Wolbachia-release areas of Betio and Bairiki or in non-release areas (all locations other than Betio and Bairiki). Laboratory-confirmed dengue cases include those with a positive dengue NS1 and/or IgM diagnostic test result recorded. Blue shading indicates the Wolbachia release period. (TIF)</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

Release & monitoring of <i>w</i>Mel-infected <i>Ae</i>. <i>aegypti</i> within six areas of Nadi and five areas of Lautoka, Fiji.

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/2007_fji_phc_admin_boundaries) and OpenMapTiles basemap layer (https://openmaptiles.org/) with CARTO light design (https://carto.com/)). (PNG)</p