Pyrethroid-resistance in Anopheles gambiae s.l (Culicidae) populations from the Sudan Savannah ecoregion in Nigeria is partly mediated by knockdown mutation

Background: Anopheles gambiae is a major malaria vector. There are documented evidences of insecticide resistance cases among mosquitoes in Nigeria and Sub-Saharan Africa. Insecticides recommended by WHO have proved to be less effective in the war against malaria and this problem seems intractable to the vector control programs. Herein we investigated prevalence of kdr gene mutation which is responsible for insecticide resistance in mosquitoes. Methods: A total of two hundred and fifty (250) Anopheles gambiae s.l mosquitoes were selected at random from the three different study locations in Kwara states, Nigeria. Morphological identification was carried out using standard keys. The insecticide susceptibility bioassay was conducted using WHO protocol. WHO impregnated insecticide papers of recommended discriminating concentrations of Permethrin (0.75%), Deltamethrin (0.05%) and Alphacypermethrin (0.05%) were used for the bioassay. Twenty-five (25) female non-blood fed Anopheles mosquitoes aged 2-5 days were introduced into WHO tubes containing a treated paper in four replicates and monitored for the number of mosquitoes that was knocked down at time intervals of; 10, 15, 20, 30, 40, 50, 60 minutes. On a subset of exposed Anopheles gambiae s.l, molecular identification of the sibling species and knock down resistance ( kdr ) gene mutation detection was carried using conventional PCR. Results: Morphological identification revealed that they were all Anopheles gambiae s.l. mosquitoes. Molecular identification revealed that seventy-eight (31.2%) of the samples were Anopheles coluzzii , forty-two (16.8%) as Anopheles gambiae s.s and thirty-four (13.6%) as Anopheles arabiensis . DNA samples of forty-six (18.4%) of the mosquito samples did not amplify at all. Analysis for kdr gene mutation showed that 104 and 146 samples were homozygous resistance and homozygous susceptible respectively. There were no observed cases of heterozygous resistance. Frequency of Kdr allele in Anopheles gambiae s.l. in Kwara State showed that homozygous resistant (RR), heterozygous resistant and homozygous susceptible (rr) 41.6%, 0.00% and 58.4% respectively. The highest percentage mortality for the three insecticides was recorded in Oyun community with 61%, 58% and 64% recorded for permethrin, deltamethrin and alphacypermethrin respectively. The lowest mortality rates for all the insecticides were recorded in the post office community with 23%, 24% and 39% mortality recorded for permethrin, deltamethrin and alphacypermethrin respectively. Result of “knockdown time” in the three (3) LGAs revealed that Permethrin had the least knockdown impact across all the LGAs while Deltamethrin had the highest percentage knockdown with KDT ₅₀ of 52.80 (47.86-59.98), 32.75 (26.04-40.38) and 38.95 (31.62-48.96) for Ilorin West, Ilorin East and Ifelodun LGAs respectively. Conclusion . This study concludes that there are cases of kdr gene mutation among An. gambiae in the three study locations in Kwara state, suggesting possibilities of high prevalence of malaria cases in the studied area. This study suggests that there should be a need to urgently and effectively monitor and address problems associated with the occurrence of insecticide-resistance in order to design effective and sustainable vector control.