Abstract:
Background & objectives: Malaria vector resistance to insecticides is a major threat to the
recent progresses in malaria control highlighting the need for continuous epidemiological
surveillance in Kenya.
Methods: WHO tube bioassay tests were used against 0.1% bendiocarb and 0.75% permethrin
on Anopheles gambiae s.l. to determine phenotypic resistance. Real-time Polymerase chain
reaction (RT-PCR) was used to identify G119S Acetylcholinesterase (ace1R) and L1014S
mutation.
Results: Anopheles arabiensis was the most prevalent species, with a frequency of 72% in
Malava, 76% in Lurambi, 68% in Mumias East and 58% in Ikolomani. Possible resistance to
bendiocarb was observed in all study sites. An. arabiensis exhibited possible resistance across
all sites, while Anopheles gambiae sensu stricto showed phenotypic resistance in Lurambi with
87.5% mortality, but fully susceptible in Malava with 100% mortality. The G119S mutation
frequency ranged from 0.6% to 2.2% in An. arabiensis while An. gambiae s.s. had a frequency
of 0.0% to 1.5%. The frequency of allele was high in An. arabiensis as compared to An.
gambiae s.s. across study sites with no significant deviation from Hardy-Weinberg equilibrium.
Interpretation & conclusion: There is widespread insecticide resistance in malaria vectors
within Kakamega County, with Anopheles arabiensis being the most prevalent species in the
County. The detection of bendiocarb possible resistance in An. arabiensis across all sites and
resistance in Anopheles gambiae s.s. suggests a challenge for vector control. The low frequency
of the G119S ace-1R mutation indicates that resistance may be due to metabolic rather than
target-site mechanisms.
