Malaria vectors resistance to insecticides in Benin: current trends and mechanisms involved.

Virgile Gnanguenon,Ramziath Agbanrinyoussouf,Roseline Attolou,Rodrigue Anagonou,Rock Aïkpon,Filemon T Tokponnon,Martin C Akogbeto,Razaki Ossè,Roseric Azondekon,Kefilath Badirou,Fiacre R Agossa,Fredéric Oke-Agbo,Renaud Govoetchan

doi:10.1186/s13071-015-0833-2

Virgile Gnanguenon, Ramziath Agbanrinyoussouf + Show 11 more

Open Access

https://doi.org/10.1186/s13071-015-0833-2

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Abstract

BackgroundInsecticides are widely used to control malaria vectors and have significantly contributed to the reduction of malaria-caused mortality. In addition, the same classes of insecticides were widely introduced and used in agriculture in Benin since 1980s. These factors probably contributed to the selection of insecticide resistance in malaria vector populations reported in several localities in Benin. This insecticide resistance represents a threat to vector control tool and should be monitored. The present study reveals observed insecticide resistance trends in Benin to help for a better management of insecticide resistance.MethodsMosquito larvae were collected in eight sites and reared in laboratory. Bioassays were conducted on the adult mosquitoes upon the four types of insecticide currently used in public health in Benin. Knock-down resistance, insensitive acetylcholinesterase-1 resistance, and metabolic resistance analysis were performed in the mosquito populations based on molecular and biochemical analysis. The data were mapped using Geographical Information Systems (GIS) with Arcgis software.ResultsMortalities observed with Deltamethrin (pyrethroid class) were less than 90% in 5 locations, between 90-97% in 2 locations, and over 98% in one location. Bendiocarb (carbamate class) showed mortalities ranged 90-97% in 2 locations and were over 98% in the others locations. A complete susceptibility to Pirimiphos methyl and Fenitrothion (organophosphate class) was observed in all locations with 98-100% mortalities. Knock-down resistance frequencies were high (0.78-0.96) and similar between Anopheles coluzzii, Anopheles gambiae, Anopheles arabiensis, and Anopheles melas. Insensitive acetylcholinesterase-1 was rare (0.002-0.1) and only detected in Anopheles gambiae in concomitance with Knock-down resistance mutation. The maps showed a large distribution of Deltamethrin resistance, Knock-down mutation and metabolic resistance throughout the country, a suspected resistance to Bendiocarb and detection of insensitive acetylcholinesterase-1 from northern Benin, and a wide distribution of susceptible vectors to Pirimiphos methyl and Fenitrothion.ConclusionThis study showed a widespread resistance of malaria vectors to pyrethroid previously located in southern Benin, an early emergence of carbamates resistance from northern Benin and a full susceptibility to organophosphates. Several resistance mechanisms were detected in vectors with a potential cross resistance to pyrethroids through Knock-down and metabolic resistance mechanisms.

Highlights

Insecticides are widely used to control malaria vectors and have significantly contributed to the reduction of malaria-caused mortality
It showed a confirmed resistance to Deltamethrin throughout the country except in Ouidah, an emerging resistance to Bendiorcarb in northern Benin, and a full susceptibility to Pirimiphos methyl and Fenitrothion with a slow effect of Fenitrothion according to WHO thresholds. These thresholds have no epidemiological meaning because the field performance of the insecticides tested remain high [31,32,33]. They were more likely designed to be the triggers of preventive action by national malaria control program to define efficient strategies to manage insecticide resistance without waiting for indisputable proof of interventions failure [24]
This study shows the resistance profile of malaria vectors to different categories of insecticides used for vector control in Benin

Summary

Introduction

Insecticides are widely used to control malaria vectors and have significantly contributed to the reduction of malaria-caused mortality. The same classes of insecticides were widely introduced and used in agriculture in Benin since 1980s These factors probably contributed to the selection of insecticide resistance in malaria vector populations reported in several localities in Benin. For malaria vector control intervention, Indoor Residual Spray and Insecticide Treated Net are so far the most effective tools used [1,2,3] These two interventions are based on the use of different classes of insecticide. Pyrethroid insecticides are considered most suitable for mosquito nets treatment due to their high insecticidal potency at low dosages and a relative safety for human contact and domestic handling [2] They included: Lambdacyhalothrin, Permethrinn, Alpha-cypermethrin, Etofenprox, and Cylfluthrin [2]. The majority of longlasting insecticide-treated nets freely distributed in all localities in Benin through mass-distribution campaigns and routine distributions since 2007 were Deltamethrin and Permethrin based [4,5,6]

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