Bionomics and insecticides resistance profiling of malaria vectors at a selected site for experimental hut trials in central Cameroon

Abstract

Background: Malaria vectors are increasingly developing resistance to insecticides across Africa. The impact of such resistance on the continued effectiveness of insecticide-based interventions remains unclear due to poor characterization of vector populations. This study reports the characterization of malaria vectors at Mibellon, a selected site in Cameroon for experimental hut study, including species composition, Plasmodium infection rate, resistance profiles and mechanisms.

Methods: Indoor resting blood-fed Anopheles mosquitoes were collected from houses at Mibellon in 2017 and forced to lay eggs to generate F₁ adult mosquitoes. Insecticides susceptibility bioassays were performed on the F₁ adult mosquitoes following the WHO protocol to assess resistance profile to insecticides. The molecular basis of resistance and Plasmodium infection rate were investigated using TaqMan genotyping.

Results: Anopheles funestus sensu stricto (s.s.) was predominant in Mibellon (80%) followed by Anopheles gambiae s.s. (20%). High levels of resistance to pyrethroids and organochlorides were observed for both species. Moderate resistance was observed against bendiocarb (carbamate) in both species, but relatively higher in An. gambiae s.s. In contrast, full susceptibility was recorded for the organophosphate malathion. The PBO synergist assays with permethrin and deltamethrin revealed a significant recovery of the susceptibility in Anopheles funestus s.s. population (48.8 to 98.1% mortality and 38.3 to 96.5% mortality, respectively). The DDT/pyrethroid 119F-GSTe2 resistant allele (28.1%) and the dieldrin 296S-RDL resistant (9.7%) were detected in An. funestus s.s. The high pyrethroid/DDT resistance in An. gambiae correlated with the high frequency of 1014F knockdown resistance allele (63.9%). The 1014S-kdr allele was detected at low frequency (1.97%). The Plasmodium infection rate was 20% in An. gambiae, whereas An. funestus exhibited an oocyst rate of 15 and 5% for the sporozoite rate.

Conclusion: These results highlight the increasing spread of insecticide resistance and the challenges that control programmes face to maintain the continued effectiveness of insecticide-based interventions.

Keywords: Cameroon; Characterization; Insecticide resistance; Malaria vectors.

Fig. 1

Susceptibility profile of Anopheles funestus to insecticides. a Recorded mortalities following 60-min exposure of An. funestus s.s. from Mibellon to different insecticides. Data are shown as mean ± SEM. b Activities of PBO combined to permethrin, deltamethrin and DDT on An. funestus s.s. from Mibellon. Data are shown as mean ± SEM

Fig. 2

Susceptibility profile of Anopheles gambiae to insecticides. Recorded mortalities following 60-min exposure of An. gambiae s.s. Mibellon to different families of insecticide. Data are shown as mean ± SEM

Fig. 3

Cone assays with various nets for Anopheles funestus and Anopheles gambiae. a Recorded mortalities following 3-min exposure by cone assay of An. funestus s.s. b Anopheles gambiae s.s. from Mibellon to Olyset, Olyset Plus, Yorkool, PermaNet 2.0 and PermaNet 3.0 (side). Data are shown as mean ± SEM

Fig. 4

Plasmodium infection rate in malaria vectors from Mibellon in 2017. a Plasmodium infection rate in An. funestus s.s. with head and thorax. b Plasmodium infection rate in An. funestus s.s. with abdomen only. (C) Plasmodium infection rate in An. gambiae s.s. for whole mosquitoes