Insecticide resistance status in anopheles Gambiae Sensu Lato (S.L.) in four malarial epidemiological zones in Kenya, 2023

Abstract

Objective: This research aimed at determining the status of insecticide resistance in the Anopheles gambiae s.l malaria vectors to  different classes of insecticides in the four malarial epidemiological zones in Kenya.

Design: A retrospective descriptive cross-sectional study of routinely collected insecticide resistance monitoring programme data.

Setting: The study considered five counties within four malarial epidemiological zones: Kwale (Coast endemic), Kirinyaga (Low  transmission zone), Nandi (Highland endemic prone zone), Baringo (Seasonal transmission zone), Marsabit(seasonal transmission zone). 

Methods: Three to five days old adult mosquitoes that emerged in the insectary from larvae collected from breeding sites in Kirinyaga,  Baringo, Kwale, Marsabit and Nandi counties were tested for susceptibility to pyrethroids, organophosphates, organochlorines and  piperonyl butoxide (PBO)-pyrethriod synergist as per WHO insecticide resistance bioassay procedure. Identification of all bioassayed  mosquitoes was done using appropriate morphological keys.

Results: Confirmed resistance in Anopheles gambiae sl. to pyrethroid  deltamethrin was observed in Kirinyaga, Kwale and Marsabit counties. Further, resistance to the pyrethroids permethrin was observed in  Kwale and to lambdacyhalothrin in Kirinyaga. The findings on susceptibility to the test insecticide were as follows; permethrin in  Kirinayaga, deltamethrin in Nandi Hills and lambdacyhalothrin in Kwale. Additionally, susceptibility of Anopheles gambiae sl. to  organochlorines, organophosphates, and PBO pyrethroid synergist was observed in Kirinyaga, Baringo and Kwale respectively.  

Conclusion: The data from the present study showed confirmed insecticide resistance majorly to the pyrethroids across the five  epidemiological zones but there was susceptibility to organochlorines, organophosphates, and synegistpyrethroid classes across all the  zones. Continued insecticide resistance monitoring and management in areas with observed resistance is key in ensuring the  effectiveness of insecticide-based vector control interventions in place.