Status and Mechanisms of Insecticide Resistance in Anopheles Mosquitoes from Mwea Sub-County and Kwale County and their Malaria Parasite Infection Rates

Abstract

Anopheles mosquitoes are vectors of malaria. Several vector control strategies have been applied to reduce human-vector contact to minimize the spread of malaria with much emphasis on control of the adult mosquitoes mainly through the use of bed nets and insecticide residual spraying (IRS). However, increasing insecticide resistance hampers the success of malaria control. The objective of this study was to determine the status and mechanism of insecticide resistance in malaria vector species from Mwea and Kwale and to determine their malaria parasite infection rates. Field collected Anopheles mosquitoes were reared in the insectary and subjected to bioassays, enzyme analysis and sporozoite tests. The bioassayed specimens were also screened for knockdown resistance (kdr) alleles. All field samples (415 from Mwea; 714 from Kwale) were identified by polymerase chain reaction. Anopheles arabiensis and An. funestus s.l. were the predominant mosquitoes in Mwea and Kwale respectively. The prevalence of malaria parasite infection was observed to be low in Mwea (0%) and slightly moderate in Kwale (10.81%). An. arabiensis from Mwea showed resistance against deltamethrin (79.24%) and permethrin (79.34%). An. funestus s.s. from Mwea were susceptible to both deltamethrin (100%) and DDT (100%). In Kwale, resistance to permethrin (71.43%) and deltamethrin (60%) was observed in An. gambiae s.s. Molecular analysis revealed an increasing frequency of kdr-east gene in Kwale (2.17%). An. gambiae s.l. from Kwale had increased ATCH, oxidase, β-esterase and GST activity against deltamethrin. Against permethrin, Kwale observed higher ATCH, oxidase, GST and β-esterase activity in the An. funestus s.l. population. The frequencies of CYP4J5 (>50%) was high in Mwea. CoE (> 25%) was high in both study sites while GSTe2 was only high in Kwale (50%). This study determined that malaria parasite infection rate was low in Mwea but high in Kwale, possibly accounting for malaria incidence in those areas. Insecticide resistance in Mwea and Kwale was observed posing a challenge on control measures. This calls for alternative control strategies to be put in place that encompasses integrated vector control methods to curtail spread of malaria in Mwea and Kwale.