Malaria Vectors Insecticide resistance profiling and Long Lasting Insecticide-treated Nets bioefficacy in Ebolowa, an urban area of South Cameroon

Abstract

BackgroundContinuous monitoring of insecticide resistance in malaria vector populations is crucial to help maintaining the efficacy of insecticide-based vector control strategies. The present study evaluated insecticide resistance in Anopheles gambaie s.l. and its impact on the efficacy of Long Lasting Insecticide-treated Nets (LLINs) in the city of Ebolowa, prior the next bednets mass distribution campaign in Cameroon.MethodsMosquitoes were collected as larvae and reared to adulthood. Females aged 3 to 4 days were exposed the insecticides according to the WHO tube test protocol, to determine their resistance profile. The bioefficacy of LLINs was determined using the WHO cone test protocol. Pyrethroids-synergist combined tests were used to search for metabolic resistance mechanisms. Molecular analysis helped investigating presence of mutations conferring resistance, as well as identifying mosquito species.ResultsAnopheles coluzzii, the dominant (99%) species of An. gambiae s.l complex found in Ebolowa, was full susceptible to Carbamates and Organophosphates, but resistant to all pyrethroids insecticides. Resistance was moderate for deltamethrin (mortality: 37%, 70% and 99% for 1x, 5x and 10x insecticide concentration, respectively) but rather high for permethrin (5% for 1x; 62% for 5x and 75% for 10x) and for alphacypermethrin (4.4% for 1x; 57% for 5x and 80% for 10x). All the LLINs tested were ineffective against the field strain with mortalities less than 50%. Synergist test indicated cytochrome P450 are fully involved in resistance against deltamethrin, but partially for the other two pyrethroids tested. The L1014F (kdr-West) mutation was present at a high frequency (75%) showing a significant association with resistance to permethrin (OR = 3.8; 95%; CI [1.9 - 7.4]; P < 0.0001) and alphacypermethrin (OR = 3; 95%; CI [1.6 - 5.4]; P = 0.0002). ConclusionThe high level of resistance to pyrethroids detected in An. colluzzii from Ebolowa is of concerns for malaria control as it threatens the efficacy of LLINs used in the city. For good management of resistance observed, the National Malaria Control Program should privilege distribution of new net formulations in this locality such as PBO-deltamethrin combined nets or new generation nets.