Re-Visiting Insecticide Resistance Status in Anopheles gambiae from Côte d'Ivoire: A Nation-Wide Informative Survey

Abstract

Insecticide resistance constitutes a major threat that may undermine current gain in malaria control in most endemic countries. National Malaria Control Programmes (NMCPs) need as much information as possible on the resistance status of malaria vectors and underlying mechanisms in order to implement the most relevant and efficient control strategy. Bioassays, biochemical and molecular analysis were performed on An. gambiae collected in six sentinel sites in Côte d'Ivoire. The sites were selected on the basis of their bioclimatic status and agricultural practices. An. gambiae populations across sites showed high levels of resistance to organochloride, pyrethroid and carbamate insecticides. The kdr and ace-1R mutations were detected in almost all sentinel sites with mosquitoes on the coastal and cotton growing areas mostly affected by these mutations. At almost all sites, the levels of detoxifying enzymes (mixed-function oxidases (MFOs), non-specific esterases (NSE) and glutathione-S-transferases (GSTs)) in An. gambiae populations were significantly higher than the levels found in the susceptible strain Kisumu. Pre-exposure of mosquitoes to PBO, an inhibitor of MFOs and NSEs, significantly increased mortality rates to pyrethroids and carbamates in mosquitoes but resistance in most cases was not fully synergised by PBO, inferring a residual role of additional mechanisms, including kdr and ace-1 site insensitivity. The large distribution of resistance in Côte d'Ivoire raises an important question of whether to continue to deploy pyrethroid-based long-lasting insecticidal nets (LLINs) and insecticide residual spraying (IRS) towards which resistance continues to rise with no guarantee that the level of resistance would not compromise their efficacy. Innovative strategies that combine insecticide and synergists in LLINs or spatially LLIN and an effective non-pyrethroid insecticide for IRS could be in the short term the best practice for the NMCP to manage insecticide resistance in malaria vectors in Côte d'Ivoire and other endemic countries facing resistance.

Anophelesbionomics, insecticide resistance mechanisms and malaria transmission in the Korhogo area, northern Côte d’Ivoire: a pre-intervention study

“…Consistent with recent studies carried out in the Korhogo area [6,25], we found very high frequencies of the kdr mutation in the An. gambiae complex population during the four surveys.…”

“…Consequently, the effectiveness of LLINs may depend on parameters such as the susceptibility of vectors to insecticides and their biting behavior. Unfortunately, resistance to the four insecticide classes used for public health (pyrethroids, organochlorines, carbamates, and organophosphates) is common in the main malaria vector species across Côte d'Ivoire [6,24,37,43]. This resistance involves multiple mechanisms such as metabolic and target site resistance.…”

“…This resistance involves multiple mechanisms such as metabolic and target site resistance. The kdr (responsible for dichlorodiphenyltrichloroethane and pyrethroids resistance) and ace-1 mutations (responsible for organophosphates and carbamates resistance) are widespread but found at variable frequencies across the country [6,24,37,43]. However, there is very little recent information on the biting behavior of malaria vector species in many areas of Côte d'Ivoire.…”

Major Disease Vectors in Tanzania: Distribution, Control and Challenges

“…Mosquito nets are treated with pyrethroids alone. Of the recent, incorporation of PBO on the LLNs has shown to increase the efficacy of the LLINs against resistant wild populations of mosquitoes [69,70]. Currently, multiple resistance interested in pyrethroid throughout the country against different vector species threatens the use of LLINs to remain as physical barrier only [68,70].…”

Long-term trends in Anopheles gambiae insecticide resistance in Côte d¿Ivoire

“…Resistance was monitored only one time in Man [9] and Abengourou [9], respectively; two times in Yamoussoukro [9,10] and San Pedro [9,11] and four times in Abidjan [9,10,12,13] and five times in Korhogo [9,10,[12][13][14].…”