Abstract
Entomological surveillance of local malaria vector populations is an important component of vector control and resistance management. In this study, the resistance profile and its possible mechanisms was characterised in a field population of the major malaria vector Anopheles coluzzii from Port Harcourt, the capital of Rivers state, in the Niger-Delta Region of Nigeria. Larvae collected in Port-Harcourt, were reared to adulthood and used for WHO bioassays. The population exhibited high resistance to permethrin, deltamethrin and DDT with mortalities of 6.7% ± 2.4, 37.5% ± 3.2 and 6.3% ± 4.1, respectively, but were fully susceptible to bendiocarb and malathion. Synergist bioassays with piperonylbutoxide (PBO) partially recovered susceptibility, with mortalities increasing to 53% ± 4, indicating probable role of CYP450s in permethrin resistance (χ2 = 29.48, P < 0.0001). Transcriptional profiling revealed five major resistance-associated genes overexpressed in the field samples compared to the fully susceptible laboratory colony, Ngoussou. Highest fold change (FC) was observed with GSTe2 (FC = 3.3 in permethrin exposed and 6.2 in unexposed) and CYP6Z3 (FC = 1.4 in exposed and 4.6 in unexposed). TaqMan genotyping of 32 F0 females detected the 1014F and 1575Y knockdown resistance (kdr) mutations with frequencies of 0.84 and 0.1, respectively, while 1014S mutation was not detected. Sequencing of a fragment of the voltage-gated sodium channel, spanning exon 20 from 13 deltamethrin-resistant and 9 susceptible females revealed only 2 distinct haplotypes with a low haplotype diversity of 0.33. The findings of high pyrethroid resistance but with a significant degree of recovery after PBO synergist assay suggests the need to move to PBO-based nets. This could be complemented with carbamate- or organophosphate-based indoor residual spraying in this area.
Highlights
Malaria kills approximately 400,000 people in 2018 alone, 93% of these deaths in the sub-Saharan Africa
The control of malaria vectors is reliant on the use of chemical insecticides through indoor residual spraying (IRS), long-lasting lasting insecticidal nets (LLINs) and Insecticide treated mosquito nets (ITNs) [2,3]
A high mortality rate (37.5%) was recorded in WHO bioassays with 0.05% deltamethrin in comparison to the very low mortality of only 6.7% ± 2.4 observed with 0.75% permethrin (Fig 2b)
Summary
Malaria kills approximately 400,000 people in 2018 alone, 93% of these deaths in the sub-Saharan Africa. The control of malaria vectors is reliant on the use of chemical insecticides through indoor residual spraying (IRS), long-lasting lasting insecticidal nets (LLINs) and Insecticide treated mosquito nets (ITNs) [2,3]. These interventions have reduced malaria transmission to half its level from year 2000 to 2015 [4]. The major threat to these recorded successes is the issue of insecticide resistance in the major malaria vectors leading to retrogression and an increase in transmission [5,6]. Adequate data gathering on the resistance profiles and mechanisms in the local malaria vector populations is a key to guide deployment of control tools using evidence-based strategies [7,8]
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