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. 2020 May 13;14(5):e0008250.
doi: 10.1371/journal.pntd.0008250. eCollection 2020 May.

Assessing entomological risk factors for arboviral disease transmission in the French Territory of the Wallis and Futuna Islands

Elodie Calvez  1 , Nicolas Pocquet  2 , Atoloto Malau  3 , Sosiasi Kilama  2 , Alefosio Taugamoa  4 , Didier Labrousse  4 , Philippe Boussès  5 , Anna-Bella Failloux  6 , Myrielle Dupont-Rouzeyrol  1 , Françoise Mathieu-Daudé  5   7
Affiliations

Assessing entomological risk factors for arboviral disease transmission in the French Territory of the Wallis and Futuna Islands

Elodie Calvez et al. PLoS Negl Trop Dis. .

Abstract

Background: The French overseas Territory of the Wallis and Futuna Islands has been affected by several dengue epidemics. Aedes polynesiensis is the main mosquito vector described in this territory. Other Aedes species have been reported, but recent entomological data are missing to infer the presence of other potential arbovirus vectors and to assess the entomological risk factors for transmission of arboviral diseases.

Methodology/ principal findings: An entomological prospective study was conducted on the three main islands of the territory to determine the presence and distribution of Aedes spp. Larvae, pupae and adult mosquitoes were collected from 54 sampling points in different environments, with a final sampling of 3747 immature stages and 606 adults. The main identified breeding sites were described. Ae. polynesiensis was found in every sampled site in peridomestic and wild habitats. Ae. aegypti was only found on the island of Wallis in peridomestic environments with a limited distribution. Two other Aedes species endemic to the Pacific were recorded, Aedes oceanicus and Aedes futunae. To evaluate the ability of local Ae. polynesiensis to transmit the chikungunya virus (CHIKV), two field populations were analyzed for vector competence using experimental oral exposure of females to CHIKV and infection, dissemination and transmission assays. Results showed that both populations of Ae. polynesiensis were competent for CHIKV (30% at 7 days post-infection).

Conclusions/significance: This study showed the ubiquitous distribution and abundance of Ae. polynesiensis on the three islands and demonstrated that local populations were able to transmit CHIKV. Combined with the presence and expansion of Ae. aegypti on the main island of Wallis, these data highlight the risk of transmission of arboviral diseases in the territory of Wallis and Futuna and provide relevant information for entomological surveillance and vector control programs.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Territory of the Wallis and Futuna Islands.
(A) Location of the Territory of the Wallis and Futuna Islands in the South Pacific represented by the red spot. (B) Map of Wallis and Futuna showing the three main islands: Wallis (78 km2) to the northeast, Futuna (46 km2) and Alofi (18 km2) to the southwest. Open source maps from USGS LandsatLook (https://landsatlook.usgs.gov/viewer.html) annotated with Adobe Photoshop 8.0.1.
Fig 2
Fig 2. Geographical location of the mosquito sampling sites and distribution of Aedes spp on Wallis and Futuna.
The numbers represent the 54 sampling points on (A) the island of Wallis, (B) the islands of Futuna and Alofi. The presence of the different Aedes species is represented by a sign near the locality name according to the legend on the map. Open source maps from USGS LandsatLook (https://landsatlook.usgs.gov/viewer.html) annotated with Adobe Photoshop 8.0.1.
Fig 3
Fig 3. Experimental infections of Aedes polynesiensis mosquitoes from Wallis with CHIKV.
(A) Infection rate, dissemination rate, transmission rate and transmission efficiency at 7 dpi for the two populations WKANA and WLALO. The percentage value and the number of positive females are indicated above each plot. (B) The titer of infectious saliva is expressed as PFU/mL/saliva for each of the 9 or 8 (for WKANA and WLALO populations, respectively) females whose saliva was tested positive. The cross indicates the median value.
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Grants and funding

This work was funded by the French Ministère des Outre-mer, DGOM (HC/DAIRCL/2180-310) (FMD) and partly supported by the Actions Concertées Inter Pasteuriennes (ZikAe project, ACIP A-15-2014) (ABF and MDR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.