Insecticide Susceptibility of An. gambiae and An. coluzzii in Congo Brazzaville

Vector control against malaria in Congo is mainly achieved through the use of long-lasting insecticide treated nets (LLINs). However, the encouraging results achieved through the use of LLINs are threatened by the proven resistance of Anopheles gambiae s.l. to pyrethroids. The aim of this study was to assess the sensitivity of Anopheles gambiae s.l. to DDT and pyrethroids, and to identify the kdr mutation and the enzymes involved in the resistance to these insecticides. Two methods were used to collect Anopheles from 2016 to 2018, 2 methods were used: collection by dipping of larvae and collection of resting females. Susceptibility testing was performed according to the WHO protocol with unfed females aged 2 - 5 days old. The insecticides used were: DDT 4%, permethrin 0.75%, deltamethrin (0.05% and 0.5%) and lambda-cyhalothrin 0.05%. The synergist piperonyl butoxide (PBO) was used to identify the enzymes involved in resistance. Polymerase chain reaction was used to identify anopheline species and kdr mutations. The tests were performed at room temperature and relative humidity of 25˚C ± 2˚C and 70% ± 10% RH respectively. Susceptibility tests showed high resistance of Anopheles to DDT and pyrethroids. Two species belonging to the Anopheles gambiae s.l. complex were identified: An. gambiae (91.4%) and An. coluzzii (8.6%). The mechanism of resistance was attributed to the kdr (knockdown resistance) L1014F mutation which confers cross-resistance to DDT and pyrethroids with a frequency ranging from 0.68 to 0.86. Monooxygenase has been identified as the enzyme involved, as it is the main enzyme involved in metabolic resistance to pyrethroids. This resistance could compromise malaria control efforts based on the use of insecticide-treated nets. However, PBO incorporated into LLINs could be effective in managing the established resistance.