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. 2022 Apr 7:5:147.
doi: 10.12688/gatesopenres.13347.2. eCollection 2021.

Environmental factors influence the local establishment of Wolbachia in Aedes aegypti mosquitoes in two small communities in central Vietnam

Nguyen T Hien  1 , Dang D Anh  1 , Nguyen H Le  1 , Nguyen T Yen  1 , Tran V Phong  1 , Vu S Nam  1 , Tran N Duong  1 , Nguyen B Nguyen  1 , Duong T T Huong  1 , Luu Q Hung  1 , Chau N T Trinh  1 , Nguyen V Hoang  1 , Vien Q Mai  2 , Le T Nghia  2 , Nguyen T Dong  2 , Le H Tho  3 , Simon Kutcher  4 , Tim P Hurst  4 , Jacqui L Montgomery  4 , Megan Woolfit  4 , Edwige Rances  4 , Peter Kyrylos  4 , Katherine L Anders  4 , Le Nguyen  4 , Jack Brown-Kenyon  4 , Angela Caird  4 , Breeanna J McLean  4 , Inaki Iturbe-Ormaetxe  4 , Scott A Ritchie  4 , Scott L O'Neill  4 , Peter A Ryan  4
Affiliations

Environmental factors influence the local establishment of Wolbachia in Aedes aegypti mosquitoes in two small communities in central Vietnam

Nguyen T Hien et al. Gates Open Res. .

Abstract

Background: The wMel strain of Wolbachia has been successfully introduced into Aedes aegypti mosquitoes and subsequently shown to reduce transmission of dengue and other pathogens, under both laboratory and field conditions. Here we describe the entomological outcomes of wMel Wolbachia mosquito releases in two small communities in Nha Trang City in central Vietnam. Methods: The wMel strain of Wolbachia was backcrossed into local Aedes aegypti genotype and mosquito releases were undertaken by community members or by staff. Field monitoring was undertaken to track Wolbachia establishment in local Ae. aegypti mosquito populations. Ecological studies were undertaken to assess relationships between environmental factors and the spatial and temporal variability in Wolbachia infection prevalence in mosquitoes. Results: Releases of wMel Wolbachia Ae. aegypti mosquitoes in two small communities in Nha Trang City resulted in the initial establishment of Wolbachia in the local Ae. aegypti mosquito populations, followed by seasonal fluctuations in Wolbachia prevalence. There was significant small-scale spatial heterogeneity in Wolbachia infection prevalence in the Tri Nguyen Village site, resulting in the loss of wMel Wolbachia infection in mosquitoes in north and center areas, despite Wolbachia prevalence remaining high in mosquitoes in the south area. In the second site, Vinh Luong Ward, Wolbachia has persisted at a high level in mosquitoes throughout this site despite similar seasonal fluctuations in wMel Wolbachia prevalence. Conclusion: Seasonal variation in Wolbachia infection prevalence in mosquitoes was associated with elevated temperature conditions, and was possibly due to imperfect maternal transmission of Wolbachia. Heterogeneity in Wolbachia infection prevalence was found throughout one site, and indicates additional factors may influence Wolbachia establishment.

Keywords: Aedes aegypti; Dengue; Wolbachia; World Mosquito Program; mosquito release.

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Conflict of interest statement

No competing interests were disclosed.

Figures

Figure 1.
Figure 1.. Map of Tri Nguyen village and Vinh Luong release areas in Nha Trang City, Vietnam.
Figure 2.
Figure 2.. Tri Nguyen village.
Figure 3.
Figure 3.. Vinh Luong Ward.
Figure 4.
Figure 4.. Mean numbers of Wolbachia mosquitoes released per house per week (black bars), and total numbers of Wolbachia mosquitoes released (red circles) in north, center and south areas in Tri Nguyen.
Figure 5.
Figure 5.. Mean numbers of Wolbachia mosquitoes released per house per week (black bars), and total numbers of Wolbachia mosquitoes released (red circles) in Vinh Luong per week.
Figure 6.
Figure 6.. Weather station data for Nha Trang (mean daily maximum temperature per week - dashed red line, mean daily temperature per week - solid black line, mean daily minimum temperature per week - dashed dark blue line, weekly rainfall - light blue bars), household temperature data (median daily temperature per week - gray line, interquartile range - box plots), and Wolbachia infection prevalence in Aedes aegypti mosquitoes in Tri Nguyen ( Wolbachia prevalence in Ae. aegypti mosquitoes, total positives / total number tested - blue line, median Wolbachia prevalence in mosquitoes per BG trap collection - red line, interquartile range - box plots, no monitoring data between July 2019 and March 2021).
Green shading represents Wolbachia mosquito release period (27 weeks).
Figure 7.
Figure 7.. Weather station data for Nha Trang (mean daily maximum temperature per week - dashed red line, mean daily temperature per week - solid black line, mean daily minimum temperature per week - dashed dark blue line, weekly rainfall - light blue bars), household temperature data (median daily temperature per week - gray line, interquartile range - box plots), and Wolbachia infection prevalence in Aedes aegypti mosquitoes in Vinh Luong ( Wolbachia prevalence in Ae. aegypti mosquitoes, total positives / total number tested - blue line, median Wolbachia prevalence in mosquitoes per BG trap collection - red line, interquartile range - box plots, no monitoring data between January 2020 and October 2020).
Green shading represents Wolbachia mosquito release period (17 weeks).
Figure 8.
Figure 8.. Wolbachia frequencies in Aedes aegypti mosquitoes collected in BG Sentinel traps in north, center and south areas in Tri Nguyen (6 November 2014 to 11 June 2018).
Figure 9.
Figure 9.. Wolbachia frequencies in Aedes aegypti mosquitoes collected in BG Sentinel traps in north, center and south areas in Tri Nguyen (4 December 2018 to 17 April 2021).
Figure 10.
Figure 10.. Wolbachia frequencies in Aedes aegypti mosquitoes collected in BG Sentinel traps in Vinh Luong (July 2018 to 27 March 2021).
Figure 11.
Figure 11.. Wolbachia frequency in Ae. aegypti immatures collected from water holding containers in north (27.1%), center (26.9%) and south (71.0%) areas in Tri Nguyen in November 2015.
Wolbachia frequency calculated based on pooled samples from all surveyed containers at each house (mean 11, range 1–27 surveyed containers per house).
Figure 12.
Figure 12.. Median (+/- interquartile range) Wolbachia density in Aedes aegypti mosquitoes collected in BGS traps per week in north, centre and south zones in Tri Nguyen (no monitoring data between July 2019 and March 2021) and in Vinh Luong (no monitoring data between January 2020 and October 2020.
Green shading represents Wolbachia mosquito release periods.
Figure 13.
Figure 13.. Mean (+/- standard deviation [SD]) numbers of Aedes aegypti mosquitoes collected in BGS traps per week in north, centre and south zones in Tri Nguyen (no monitoring data between July 2019 and March 2021) and in Vinh Luong (no monitoring data between January 2020 and October 2020).
Green shading represents Wolbachia mosquito release periods.
See this image and copyright information in PMC

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