Elevated Plasmodium infection and multiple insecticide resistance in the principal malaria vectors Anopheles funestus and Anopheles gambiae in a forested locality close to the airport of Yaoundé, the Capital city of Cameroon

Abstract

Background Reducing the burden of malaria requires better understanding of vector populations particularly in forested regions where the incidence remains elevated. Here, we characterized malaria vectors in a locality near the international airport of Yaoundé, the capital city of Cameroon, including species composition, abundance, Plasmodium infection rate; insecticide resistance profiles and underlying resistance mechanisms. Methods Blood-fed adult mosquitoes resting indoors were aspirated from houses in April 2019 at Elende, a village located 2km from the Yaoundé-Nsimalen airport. Female mosquitoes were forced to lay eggs to generate F 1 adult progeny. WHO bioassays were performed to assess resistance profile to insecticides. The threshold of insecticide susceptibility was fixed above 98% mortality rate and mortality rates below 90% were considered indicative of confirmed insecticide resistance according to the WHO test procedures for insecticide resistance monitoring. Furthermore, the molecular basis of resistance and Plasmodium infection rates were investigated.Results Anopheles funestus s.s. was most abundant species in Elende (85%) followed by Anopheles gambiae s.s. (15%) with both having a similar sporozoite infection rate. Both species exhibited high levels of resistance to pyrethroids (<40% mortality). An. gambiae s.s. was also resistant to DDT (9.9% mortality) and bendiocarb (54% mortality) while susceptible to organophosphate. An. funestus s.s. was resistant to dieldrin (1% mortality), DDT (86% mortality) but susceptible to carbamates and organophosphates. The DDT/pyrethroid L119F-GSTe2 resistance allele (8%) and G119S ace -1 resistance allele (15%) were detected in An. funestus s.s. and An. gambiae s.s. respectively. Furthermore, the high pyrethroid/DDT resistances in An. gambiae s.s. corresponded with an increase frequency of 1014F kdr allele (95%). The CYP6P9a P450 resistance allele was absent in the An. funestus s.s. population meanwhile transcriptional profiling of candidate cytochrome P450 genes reveals the over-expression of CYP6P5 , CYP6P9a and CYP6P9b. Conclusion The resistance to multiple insecticide classes observed in these vector populations alongside the high Plasmodium infection rate highlights the challenges that public health vector control programs encounter in sustaining the regular effectiveness of contemporary insecticide-based control interventions in forested areas. More particularly, the resistance observed against the carbamates and possible resistance against the organophosphates constitutes a major concern for IRS.

Multiple insecticide resistance and Plasmodium infection in the principal malaria vectors Anopheles funestus and Anopheles gambiae in a forested locality close to the Yaoundé airport, Cameroon

“…gambiae s.s., 5.13% [(02/39) (CI: 2.57-7.13)] were infected with P. falciparum and none for P. OVM or mixed infections. Nested PCR confirmed 1 positive P. falciparum sample out of the 2 infected samples detected by TaqMan assay (see Underlying data for raw values 34 ).…”

“…Resistance to the carbamate insecticide, bendiocarb was recorded with a mortality value of 54.56±1.05% ( Figure 2b ). Moreover, for the organophosphate insecticides, mortality rates of 95.24±1.94%, 95.23±0.09%, and 96.75±1.63% were observed for malathion, fenithrothion and pirimiphos-methyl respectively ( Figure 2b ) suggesting possible resistance that necessitates further confirmation (see Underlying data 34 ).…”

“…The susceptible strain for An. funestus FANG, used as control demonstrated full mortality to all nets ( Figure 3b ) (see Underlying data 34 ).…”

“…Initial exposure of 169 F 1 An. funestus s.s. mosquitoes to PBO led to return of susceptibility to both class I and II pyrethroids with full mortality recorded after PBO + pyrethroid exposure from 51.50±7.19% to 100% for permethrin and from 19.22±10.76% to 100% mortality for deltamethrin ( Figure 3a ) (see Underlying data 34 ). Briefly, the number of mosquitoes per treatment includes: permethrin (n=85), PBO + permethrin (n=80), deltamethrin (n=96), PBO + deltamethrin (n=89), PBO only (n=74) and control (n=65).…”

“…funestus s.s. and 20 (51.28%) An. gambiae s.s. laid eggs respectively by the forced egg laying technique (see Underlying data for raw PCR values 34 ).…”