Status and Mechanisms of Insecticide Resistance in Vectors of Malaria within Kilifi County along Coastal Kenya

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Munywoki, Nzioka Daniel
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Kenyatta University
Vector control is key to reduction of malaria transmission. In sub-Saharan Africa, vector control programmes are mainly dependent on insecticide treated nets (ITNs) or indoor residual spraying (IRS). However, the progress, as a result of these methods, is currently under threat due to the fast and continuing evolution of insecticide resistance by malaria vectors. Knowledge on the resistance status of mosquito populations and the mechanisms involved form the basis for the development of sound plan for resistance control and management. This study investigated the resistance status of selected insecticides recommended by World Health Organization Pesticides Evaluation Scheme for control of mosquitoes. Anopheles gambiae s.l. larvae collected from eight study sites (Burangi, Jaribuni, Kidutani, Mangororo, Mapawa, Mbogolo, Ng’ombeni and Shibe) in Kilifi county were reared up to adulthood in the insectary. From this colony, 3-5 day old non-blood fed females were obtained and tested following the World Health Organization (WHO) procedures for susceptibility to fenitrothion (1%), bendiocarb (0.1%), permethrin (0.75%), deltamethrin (0.05%) and DDT (4%). The knockdown time (KDT) for each insecticide was recorded up to 60 minutes while final mortality was noted after 24 hours post-exposure. Polymerase chain reaction (PCR) amplification of rDNA intergenic spacers was used for identification of the sibling species of the Anopheles gambiae complex. In addition, 192 Anopheles gambiae s.l mosquitoes were used to determine the genotype constitution at amino acid 1014 of the voltage-gated sodium channel using real time polymerase chain reaction. The data for resistance was classified following World Health Organization criteria with, mortality rates of 98-100% indicating susceptibility, 90-97% possible resistance that requires further confirmation and ≤90% indicating resistance. The knockdown times at 50% and 95% of the mosquitoes were estimated using probit analysis. Final data were entered into Microsoft excel 2010 and analyzed using the R statistical software version 3.2.2. The results indicated that, Anopheles arabiensis was the dominant species representing 95.2% of the total collections followed by Anopheles gambiae s.s. at 4.8%. The percentage mortality rates indicated resistance to pyrethroids (deltamethrin and permethrin) in Burangi and organophosphate (fenitrothion) in Jaribuni villages. The L1014F knockdown (kdr) mutation was not found in both An. gambiae s.s and An. arabiensis. However, L1014S kdr mutation was discovered in An. gambiae s.s at an allele frequency of 3.33%. The findings from this study provide essential information to the Ministry of Health and public health stakeholders necessary for monitoring the establishment of insecticide resistance and development of management strategies to delay or mitigate its impact on vector control.
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Applied Medical Entomology) in the School of Pure and Applied Sciences of Kenyatta University, June, 2022
Status and Mechanisms, Insecticide Resistance, Vectors, Malaria, Kilifi County, Coastal Kenya