The current insecticide resistance status of Anopheles gambiae (s.l.) (Culicidae) in rural and urban areas of Bouaké, Côte d’Ivoire

Abstract

BackgroundSeveral studies were carried out in experimental hut station in areas surrounding the city of Bouaké, after the crisis in Côte d’Ivoire. They reported increasing resistance levels to insecticide for malaria transmiting mosquitoes. The present work aims to evaluate the current resistance level of An. gambiae (s.l.) in rural and urban areas in the city of Bouaké.MethodsLarvae of Anopheles gambiae (s.l.) were collected from five different study sites and reared to adult stages. The resistance status was assessed using the WHO bioassay test kits for adult mosquitoes, with eight insecticides belonging to pyrethroids, organochlorines, carbamates and organophosphates classes. Molecular assays were performed to identify the molecular forms of An. gambiae (s.l.), the L1014F kdr and the ace-1R alleles in individual mosquitoes. The synergist PBO was used to investigate the role of enzymes in resistance. Biochemical assays were performed to detect potential increased activities in mixed function oxidase (MFO) levels, non-specific esterases (NSE) and glutathione S-transferases (GST).ResultsHigh resistance levels to pyrethroids, organochlorines, and carbamates were observed in Anopheles gambiae (s.l.) from Bouaké. Mortalities ranged between 0 and 73% for the eight tested insecticides. The pre-exposure to PBO restored full or partial susceptibility to pyrethroids in the different sites. The same trend was observed with the carbamates in five sites, but to a lesser extent. With DDT, pre-exposure to PBO did not increase the mortality rate of An. gambiae (s.l.) from the same sites. Tolerance to organophosphates was observed. An increased activity of NSE and higher level of MFO were found compared to the Kisumu susceptible reference strain. Two molecular forms, S form [(An. gambiae (s.s)] and M form (An. coluzzi) were identified. The kdr allele frequencies vary from 85.9 to 99.8% for An. gambiae (s.s.) and from 81.7 to 99.6% for An. coluzzii. The ace-1R frequencies vary between 25.6 and 38.8% for An. gambiae (s.s.) and from 28.6 to 36.7% for An. coluzzii.ConclusionResistance to insecticides is widespread within both An. gambiae (s.s.) and An. coluzzii. Two mechanisms of resistance, i.e. metabolic and target-site mutation seemed to largely explain the high resistance level of mosquitoes in Bouaké. Pyrethroid resistance was found exclusively due to the metabolic mechanism.

Multiple Insecticide Resistance Target Sites in Adult Field Strains of An. Gambiae s.l. From Southeast Senegal.

“…These insecticides are the only ones currently approved for LLIN treatment [25,26] The use of LLINs over several years could have led to the increase of resistance genes in vectors of An. gambiae species complex, through selection pressure [27,35]. The resistance of An.…”

Characterizing the molecular and metabolic mechanisms of insecticide resistance in Anopheles gambiae s.l. in Faranah, Guinea

“…An. gambiae s.s. breed in temporary, rain-dependent breeding sites [32], which could account for its predominance during the rainy season. Future collections at multiple timepoints, utilizing different collection methods would be necessary to determine the principal species in the area.…”

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

“…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.…”