Insecticide resistance status of Anopheles gambiae s.s population from M’Bé: a WHOPES-labelled experimental hut station, 10 years after the political crisis in Côte d’Ivoire

Abstract

BackgroundAn experimental hut station built at M’Bé in 1998 was used for many years for the evaluation of insecticidal product for public health until the civil war broke out in 2002. Breeding sites of mosquitoes and selection pressure in the area were maintained by local farming practices and the West African Rice Development Association (WARDA, actually AfricaRice) in a large rice growing area. Ten years after the crisis, bioassays, molecular and biochemical analyses were conducted to update the resistance status and study the evolution of resistance mechanisms of Anopheles gambiae s.s population.MethodsAnopheles gambiae s.s larvae from M’Bé were collected in breeding sites and reared until emergence. Resistance status of this population to conventional insecticides was assessed using WHO bioassay test kits for adult mosquitoes, with 10 insecticides belonging to pyrethroids, pseudo-pyrethroid, organochlorides, carbamates and organophosphates with and without the inhibitor piperonyl butoxyde (PBO). Molecular and biochemical assays were carried out to identify the L1014F kdr, L1014S kdr and ace-1R alleles in individual mosquitoes and to detect potential increase in mixed function oxidases (MFO) level, non-specific esterases (NSE) and glutathione S-transferases (GST) activities.Results and discussionAnopheles gambiae s.s from M’Bé exerted high resistance levels to organochlorides, pyrethroids, and carbamates. Mortalities ranged from 3% to 21% for organochlorides, from 50% to 75% for pyrethroids, 34% for etofenprox, the pseudo-pyrethroid, and from 7% to 80% for carbamates. Tolerance to organophosphates was observed with mortalities ranging from 95% to 98%. Bioassays run with a pre-exposition of mosquitoes to PBO induced very high levels of mortalities compared to the bioassays without PBO, suggesting that the resistance to pyrethroid and carbamate relied largely on detoxifying enzymes’ activities. The L1014F kdr allelic frequency was 0.33 in 2012 compared to 0.05 before the crisis in 2002. Neither the L1014S kdr nor ace-1R mutations were detected. An increased activity of NSE and level of MFO was found relative to the reference strain Kisumu. This was the first evidence of metabolic resistance based resistance in An. gambiae s.s from M’Bé.ConclusionThe An. gambiae s.s population showed very high resistance to organochlorides, pyrethroids and carbamates. This resistance level relied largely on two major types of resistance: metabolic and target-site mutation. This multifactorial resistance offers a unique opportunity to evaluate the impact of both mechanisms and their interaction with the vector control tools currently used or in development.

Adaptive deletion in resistance gene duplications in the malaria vector Anopheles gambiae

“…is globally more resistant than An. coluzzii (Table 1 and Figure 4), an observation consistent with previous reports from several West African countries (Dabiré et al., 2009; Djogbénou, Akogbéto, & Chandre, 2008; Djogbénou, Chandre et al., 2008; Djogbénou et al., 2009; Essandoh, Yawson, & Weetman, 2013; Weetman et al., 2015), although not all (see Ahoua Alou et al., 2010; Koffi, Ahoua Alou, Adja, Chandre, & Pennetier, 2013 for data from Ivory Coast localities). These differences can be particularly striking in samples where both species coexist: for example, in Natitingou 2017, the frequency of resistance alleles is about 0.8 in An.…”

Empirical and theoretical investigation into the potential impacts of insecticide resistance on the effectiveness of insecticide‐treated bed nets

“…(99% M‐form, now classified as An. coluzzi ) and exhibit intense pyrethroid resistance due to both kdr and metabolic mechanisms (Koffi, Ahoua Alou, Adja, Chandre, & Pennetier, ; Koffi et al., ). CDC assays indicate >1,700‐fold resistance to deltamethrin relative to a standard susceptible strain (see ).…”

“…To complement the laboratory‐based experiments, we extended our investigations to the field, using experimental huts in an area of known pyrethroid resistance in central Côte d'Ivoire (Koffi et al., , ) to examine the effectiveness of a standard LLIN (PermaNet 2.0) against naturally recruiting wild mosquitoes. Huts were the typical West African experimental hut design (World Health Organization ) with LLIN and untreated control nets damaged according to standard protocols (Koffi et al., ; World Health Organization ) to enable mosquitoes to take blood meals.…”

Insecticide Resistance and Fitness Cost

“…The main mechanisms that led them to become highly resistant to OC, PY, and CA were the L1014F kdr mutation and elevated activity of MFO and EST. The only well-known contexts that might explain this severe shift from susceptible to highly resistant were the pressure with deltamethrin-based products from rice paddles and the distribution of long-lasting PY impregnated nets (LLINs) since 2006 [56]. The alteration in the resistance profile over the time would suggest a low cost of the resistance alleles.…”