First report of natural infection of Anopheles gambiae s.s. and Anopheles coluzzii by Wolbachia and Microsporidia in Benin: a cross-sectional study.

BACKGROUND: Recently, bacterial endosymbiont, including Wolbachia and Microsporidia were found to limit the infection of Anopheles mosquitoes with Plasmodium falciparum. This study aimed to investigate the natural presence of key transmission-blocking endosymbionts in Anopheles gambiae and Anopheles coluzzii in Southern Benin. METHODS: The present study was conducted in seven communes (Cotonou, Porto-Novo, Aguégués, Ifangni, Pobè Athiémé, and Grand-Popo) of Southern Benin. Anopheles were collected using indoor/outdoor Human Landing Catches (HLCs) and Pyrethrum Spray Catches (PSCs). Following morphological identification, PCR was used to identify An. gambiae sensu lato (s.l.) to species level and to screen for the presence of both Wolbachia and Microsporidia. Plasmodium falciparum sporozoite infection was also assessed using ELISA. RESULTS: Overall, species composition in An. gambiae s.l. was 53.7% An. coluzzii, while the remainder was An. gambiae sensu stricto (s.s.). Combined data of the two sampling techniques revealed a mean infection prevalence with Wolbachia of 5.1% (95% CI 0.90-18.6) and 1.3% (95% CI 0.07-7.8) in An. gambiae s.s. and An. coluzzii, respectively. The mean infection prevalence with Microsporidia was 41.0% (95% CI 25.9-57.8) for An. gambiae s.s. and 57.0% (95% CI 45.4-67.9) for An. coluzzii. Wolbachia was only observed in Ifangni, Pobè, and Cotonou, while Microsporidia was detected in all study communes. Aggregated data for HLCs and PSCs showed a sporozoite rate (SR) of 0.80% (95% CI 0.09-2.87) and 0.69% (95% CI 0.09-2.87) for An. gambiae and An. coluzzii, respectively, with a mean of 0.74% (95% CI 0.20-1.90). Of the four individual mosquitoes which harboured P. falciparum, none were also infected with Wolbachia and one contained Microsporidia. CONCLUSIONS: The present study is the first report of natural infections of field-collected An. gambiae s.l. populations from Benin with Wolbachia and Microsporidia. Sustained efforts should be made to widen the spectrum of bacteria identified in mosquitoes, with the potential to develop endosymbiont-based control tools; such interventions could be the game-changer in the control of malaria and arboviral disease transmission.

Bio-efficacy of Olyset® Plus, PermaNet® 3.0 and Interceptor® G2 on pyrethroid-resistant populations of Anopheles gambiae s.l. prior to the June 2023 net distribution campaign in Benin, West Africa.

BACKGROUND: This study investigates the effectiveness of new-generation mosquito nets, like Olyset® Plus and PermaNet® 3.0, and dual-action nets such as Interceptor® G2, against pyrethroid-resistant Anopheles gambiae mosquitoes following the 2023 mass distribution of long-lasting insecticidal nets in Benin. METHODS: We tested wild mosquito populations from six communes in Benin against various pyrethroid (permethrin 0.75%, alphacypermethrin 0.05%, and deltamethrin 0.05%) using WHO tube tests. Additionally, we exposed mosquitoes to chlorfenapyr 100 µg/ml using the CDC bottle bioassay method. A subset of mosquitoes underwent biochemical and PCR tests to check the overexpression of metabolic enzymes and the Kdr L1014F mutation. We evaluated the effectiveness of Olyset® Plus, PermaNet® 3.0, and Interceptor® G2 nets using cone and tunnel tests on both laboratory and field populations of An. gambiae. RESULTS: Overall, the highest mortality rate was 60% with pyrethroid and 98 to100% with chlorfenapyr. In cone tests, all three types of nets induced mortality rates above 80% in the susceptible laboratory strain of An. gambiae. Notably, Olyset® Plus showed the highest mortality rates for pyrethroid-resistant mosquitoes in cone tests, ranging from 81.03% (95% CI: 68.59-90.13) in Djougou to 96.08% (95% CI: 86.54-99.52) in Akpro-Missérété. PermaNet® 3.0 had variable rates, from 42.5% (95% CI: 27.04-59.11) in Djougou to 58.54% (95% CI: 42.11-73.68) in Porto-Novo. However, revealed good results for Interceptor® G2, with 94% (95% CI: 87.40-97.77) mortality and 89.09% blood sampling inhibition in local populations of An. gambiae. In comparison, Interceptor® had lower rates of 17% (95% CI: 10.23-25.82) and 60%, respectively. CONCLUSION: These results suggest that tunnel tests are effective for evaluating dual-active ingredient nets. Additionally, Interceptor® G2 and PBO nets like Olyset® Plus could be considered as alternatives against pyrethroid-resistant mosquitoes.

Detection of DENV-1, DENV-3, and DENV-4 Serotypes in Aedes aegypti and Aedes albopictus, and Epidemic Risk in the Departments of Oueme and Plateau, South-Eastern Benin.

Background: This study conducted in the departments of Oueme and Plateau aims to assess the presence of the dengue virus and its different serotypes in Aedes aegypti and Aedes albopictus, as well as the epidemic risk incurred by the populations. Methods: Collections of adult mosquitoes using human landing catches (HLC) were carried out in six communes, three (Porto-Novo, Adjarra, and Avrankou) in the Oueme department and the rest (Ifangni, Kétou, and Pobè) in the Plateau department. Pools of ten Aedes mosquitoes were formed, and stored at -80°C in RNA later. RT-PCR was used to detect dengue virus, and conventional PCR for the different serotypes. Inspection of water containers and collection of Aedes larvae was performed inside and around each house to calculate the stegomyan indices. Results: In the six communes, the dengue virus was present both in Ae. aegypti and Ae. albopictus. Combined data of the two Aedes species at the communes level revealed infection rates ranging from 80.00% (95% CI: 61.43-92.29) to 96.67% (95% CI: 82.78-99.92). In all the communes, the values of stegomyan indices reached the WHO threshold, which indicates the existence of the risk of an arbovirus epidemic. In addition, the infection rates were similar for Ae. aegypti [88.19% (95% CI: 81.27-93.24)] and Ae. albopictus [86.79% (95% CI: 74.66-94.52)]. The three virus serotypes detected in the pools of Aedes were DENV-1, DENV-3, and DENV-4, with a high prevalence for the first two. Conclusion: This study revealed that three serotypes (DENV-1, DENV-3, and DENV-4) of dengue virus circulate in Ae. aegypti and Ae. albopictus in the departments of Oueme and Plateau. Moreover, the risk of transmission of arboviruses was globally high and variable from commune to commune. This information is essential for informed decision-making in the preventive control of the disease.