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.

The Attractiveness of the Gravid Aedes Trap to Dengue Vectors in Fiji.

The Gravid Aedes Trap (GAT) is a passive trap that relies on visual and olfactory cues to lure and capture gravid mosquitoes. The GAT was designed as a dengue vector surveillance tool for use in conditions where power sources are not readily available. Experiments were conducted over a 10-d period in Fiji to determine which species of mosquitoes the GAT would collect, how different infusion types affect the attractiveness of the trap, how long each infusion type took to begin attracting mosquitoes, and how long the infusion was attractive to container breeding Aedes mosquitoes. Infusions were created by adding 10 g of organic material to 2 liters of water. Infusions were made using chicken feed pellets, dried mango leaves (Mangifera indica), and dried lawn grasses (primarily Axonopus spp.). The GAT collected four different vectors Aedes aegypti (Linnaeus) (Diptera: Culicidae), Aedes albopictus (Skuse) (Diptera: Culicidae), Aedes polynesiensis Mark (Diptera: Culicidae), and Culex quinquefasciatus Say (Diptera: Culicidae). As observed in previous studies, using some type of organic infusion improved the attractiveness of the trap. Of the three different infusion components tested, chicken feed was most attractive followed by lawn grasses and mango leaves. All infusions performed better than plain water. Chicken feed was found to be most attractive for Ae. aegypti and Ae. albopictus during the first 6 d after placing the traps and for Cx. quinquifasciatus in days 7-9. The mango and grass infusions took longer to attract mosquitoes but were most attractive during days 7-10 for all species.

Genetic Diversity and Phylogeny of Aedes aegypti, the Main Arbovirus Vector in the Pacific.

BACKGROUND: The Pacific region is an area unique in the world, composed of thousands of islands with differing climates and environments. The spreading and establishment of the mosquito Aedes aegypti in these islands might be linked to human migration. Ae. aegypti is the major vector of arboviruses (dengue, chikungunya and Zika viruses) in the region. The intense circulation of these viruses in the Pacific during the last decade led to an increase of vector control measures by local health authorities. The aim of this study is to analyze the genetic relationships among Ae. aegypti populations in this region. METHODOLOGY/PRINCIPAL FINDING: We studied the genetic variability and population genetics of 270 Ae. aegypti, sampled from 9 locations in New Caledonia, Fiji, Tonga and French Polynesia by analyzing nine microsatellites and two mitochondrial DNA regions (CO1 and ND4). Microsatellite markers revealed heterogeneity in the genetic structure between the western, central and eastern Pacific island countries. The microsatellite markers indicate a statistically moderate differentiation (FST = 0.136; P < = 0.001) in relation to island isolation. A high degree of mixed ancestry can be observed in the most important towns (e.g. Noumea, Suva and Papeete) compared with the most isolated islands (e.g. Ouvea and Vaitahu). Phylogenetic analysis indicated that most of samples are related to Asian and American specimens. CONCLUSIONS/SIGNIFICANCE: Our results suggest a link between human migrations in the Pacific region and the origin of Ae. aegypti populations. The genetic pattern observed might be linked to the island isolation and to the different environmental conditions or ecosystems.