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Impact of glutathione-s transferase and cytochrome P450 metabolic resistance on the effectiveness of various bed nets against Anopheles funestus, a major malaria vector in Africa

Menze, Benjamin (2020) Impact of glutathione-s transferase and cytochrome P450 metabolic resistance on the effectiveness of various bed nets against Anopheles funestus, a major malaria vector in Africa, Thesis (Doctoral), Liverpool School of Tropical Medicine.

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The scale-up of insecticide-based interventions, including Indoor Residual Spraying (IRS) and Long Lasting Insecticidal Nets (LLINs), has contributed to the significant reduction of malaria burden in the past decade. Unfortunately, growing insecticide resistance in malaria vectors is threatening these successes. However, the impact of resistance, especially metabolic resistance, on the effectiveness of vector control tools against pyrethroid-resistant mosquito populations, remains a topic of debate. One of the key challenges of assessing the impact of metabolic resistance on the effectiveness of these insecticide-based interventions has been the lack of molecular markers for insecticide resistance, notably metabolic resistance. The recent detection of key genetic markers conferring metabolic-mediated resistance (GSTe2 marker and CYP6P9a/b markers) is providing the opportunity to now address this question. In this work, we used an experimental hut trial, and the markers recently made available to investigate the direct impact of metabolic resistance on the effectiveness of insecticide-based interventions.
The characterization of the area selected for experimental hut trial revealed that Anopheles funestus sensu stricto (s.s.) (80%) and Anopheles gambiae s.s. (20%) are the two main species. High levels of resistance to pyrethroids and organochlorines were noticed. Moderate resistance was observed against bendiocarb (carbamate) in both species, but relatively higher in Anopheles gambiae s.s. In contrast, full susceptibility was observed for the organophosphate malathion. The PBO synergist assays with pyrethroid type I and II 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 resistance (9.7%) were detected in Anopheles funestus s.s. The high pyrethroid/DDT resistance in Anopheles gambiae correlated with the high frequency of the 1014F knockdown resistance allele (63.9%). The 1014S-kdr allele was detected at low frequency (1.97%). The Plasmodium infection rate was 20% in Anopheles gambiae, whereas Anopheles funestus exhibited an oocyst infection rate of 15 and 5% for the sporozoite infection rate. Using experimental hut trials and genotyping of a glutathione S-transferase resistance marker (L119F-GSTe2), we noticed that PBO-based nets induced a significantly higher mortality rate than pyrethroid-only nets. Blood feeding rate and deterrence were significantly higher in all LLINs than control, although greater for PermaNet 3.0 than PermaNet 2.0 but not between Olyset nets. Genotyping the the L119F-GSTe2 mutation revealed that, for permethrin-based nets, 119F-GSTe2 resistant mosquitoes have a greater ability to blood feed than susceptible [Olyset Plus (OR= 3.1; P=0.00007) and Olyset (OR=3.0; P=0.00007)] while the opposite effect is observed for deltamethrin-based nets. For Olyset Plus, a significant association with exophily was observed in resistant mosquitoes (OR=11.7; P=0.003). Furthermore, GSTe2-resistant mosquitoes (cone assays) significantly survived with PermaNet 2.0 (OR=2.1; P=0.002) and even more with PermaNet 3.0 (OR=30.1; P<0.0001) whereas no association was observed for Olyset Plus. L119F-GSTe2 was confirmed to confer resistance to permethrin, Deltamethrin, and DDT. Also, genotyping of the CYP6P9a/b markers revealed that homozygous resistant (RR) were better able to survive exposure to Olyset nets than homozygous susceptible (SS) : (OR=7.03; P< 0.01) for CYP6P9a and (OR=5.1; P<0.01) for CYP6P9b. In addition, homozygous resistant (RR) show a greater ability to blood feed when compared to homozygous susceptible (SS) (OR= 3.1; p<0.001) for CYP6P9a and (OR= 8.01; p<0.001) for CYP6P9b. Further analysis demonstrates that mosquitoes double homozygous resistant (RR/RR) at both genes had by far a significant ability to reduce LLINs efficacy (Blood feeding: RR/RR v SS/SS; OR= 9.3; p<0.001) compared to single homozygous (Blood feeding RR v SS; OR= 4.5; p<0.001).
This study shows the greater efficacy of PBO-based nets against pyrethroid-resistant malaria vectors. Reduced efficiency of LLINs and the increased ability to survive and blood feed of CYP6P9a/b and GSTe2 resistant mosquitoes highlight the impact of metabolic resistance.

Item Type: Thesis (Doctoral)
Subjects: QX Parasitology > Insects. Other Parasites > QX 515 Anopheles
QX Parasitology > Insects. Other Parasites > QX 650 Insect vectors
WA Public Health > Preventive Medicine > WA 110 Prevention and control of communicable diseases. Transmission of infectious diseases
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 750 Malaria
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 765 Prevention and control
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Item titleItem URI
An Experimental Hut Evaluation of PBO-Based and Pyrethroid-Only Nets against the Malaria Vector Anopheles funestus Reveals a Loss of Bed Nets Efficacy Associated with GSTe2 Metabolic Resistance
A cytochrome P450 allele confers pyrethroid resistance on a major African malaria vector, reducing insecticide-treated bednet efficacy
Bionomics and insecticides resistance profiling of malaria vectors at a selected site for experimental hut trials in central Cameroon
Cis-regulatory CYP6P9b P450 variants associated with loss of insecticide-treated bed net efficacy against Anopheles funestus
Faculty: Department: Biological Sciences > Vector Biology Department
Depositing User: Lynn Roberts-Maloney
Date Deposited: 16 Mar 2021 15:47
Last Modified: 16 Jun 2021 01:02


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