Marked aggravation of pyrethroid resistance in major malaria vectors in Malawi between 2014 and 2021 is partly linked with increased expression of P450 alleles

Abstract Background Increased intensity of pyrethroid resistance is threatening the effectiveness of insecticide-based interventions to control malaria in Africa. Assessing the extent of this aggravation and its impact on the efficacy of these tools is vital to ensure the continued control of major vectors. Here we took advantage of 2009 and 2014 data from Malawi to establish the extent of the resistance escalation in 2021 and assessed its impact on various bed nets performance. Methods Indoor blood-fed and wild female Anopheles (An) mosquitoes were collected with an electric aspirator in Chikwawa. Cocktail and SINE PCR were used to identify sibling species belonging to An. funestus group and An. gambiae complex. The susceptibility profile to the four classes of insecticides was assessed using the WHO tubes bioassays. Data were saved in an Excel file. Analysis was done using Vassarstats and figures by Graph Pad. Results In this study, a high level of resistance was observed with pyrethroids (permethrin, deltamethrin and alpha-cypermethrin with mortality rate at 5x discriminating concentration (DC)