High Plasmodium Infection Rate and Reduced Bed Net Efficacy in Multiple Insecticide-Resistant Malaria Vectors in Kinshasa, Democratic Republic of Congo

Abstract

Accounting for approximately 11% of all malaria cases, the Democratic Republic of the Congo (DRC) is central to malaria elimination efforts. To support vector control interventions in DRC, we characterized the dynamics and impact of insecticide resistance in major malaria vectors in 2015. High Plasmodium infection rates were recorded in Anopheles gambiae and Anopheles funestus, with Plasmodium falciparum predominant over Plasmodium malariae. Both mosquito species exhibited high and multiple resistance to major public health insecticide classes. The extremely high resistance to permethrin and DDT (dichlorodiphenyltrichloroethane) in An. gambiae (low mortalities after 6 hours exposure) is worrisome, and is supported by a reduced insecticidal effect of bed nets against both mosquito species in laboratory tests. Metabolic and target site insensitivity mechanisms are driving this resistance in An. gambiae, but only the former was observed in An. funestus. These findings highlight the urgent need for actions to prolong the effectiveness of insecticide-based interventions in DRC.

Keywords: Anopheles; Democratic Republic of Congo; Plasmodium falciparum; insecticide resistance; malaria.

Figure 1.

Susceptibility profile of Anopheles gambiae sensu lato population in Kinshasa using World Health Organization insecticide susceptibility tube assays with 60 minutes of exposure (A) and for females at different time points (B). Error bars represent standard error of the mean. Abbreviations: DDT, dichlorodiphenyltrichloroethane; NM, no mortality.

Figure 2.

Susceptibility profile of Anopheles funestus sensu stricto population using World Health Organization insecticide susceptibility tube assays in Kinshasa. Error bars represent standard error of the mean. Abbreviations: DDT, dichlorodiphenyltrichloroethane; NT, not tested.

Figure 3.

Synergist and bed net efficacy tests. A, Susceptibility profile of Anopheles gambiae sensu lato after synergist assay with piperonyl butoxide. B, Bioefficacy of different commercial long-lasting insecticidal nets against An. gambiae sensu lato and Anopheles funestus sensu stricto. Error bars represent standard error of the mean. Abbreviations: DDT, dichlorodiphenyltrichloroethane; NM, no mortality; PBO, piperonyl butoxide.

Figure 4.

Analysis of the polymorphism of a portion of the voltage-gated sodium channel (VGSC) gene spanning the L1014F/S mutation. A, Distribution of the genotypes at the 1014 codon position. B, Maximum likelihood phylogenetic tree of VGSC fragment with previously recorded 1014F/S haplotypes across Africa [21]. C, Templeton-Crandall-Singh network for the VGSC haplotypes between susceptible and resistant permethrin samples in Kinshasa. Haplotypes are represented as an oval or a rectangle, scaled to reflect their frequencies. Lines connecting haplotypes and each node represent a single mutation event (respective polymorphic positions are given above branches). D, Sequencing traces showing the polymorphic positions 91 and 92 generating the third 1014S haplotype newly detected in Congo and suggesting an independent occurrence of 1014S.

Figure 5.

Investigation of molecular basis of resistance in Anopheles funestus. A, Distribution of the genotypes at the A296S RDL resistance marker. B, Distribution of the genotypes at the L119F resistance marker of the GSTE2 gene. C, Differential expression by quantitative reverse-transcription polymerase chain reaction of the major insecticide resistance genes in An. funestus sensu stricto in Kinshasa compared with the susceptible An. funestus sensu stricto strain FANG. Error bars represent standard error of the mean. **P < 0.01; ***P < 0. 001.