Increased prevalence of insecticide resistance in Anopheles coluzzii populations in the city of Yaoundé, Cameroon and influence on pyrethroid-only treated bed net efficacy.

Roland Bamou,Edmond Kopya,Timoléon Tchuinkam,Christophe Antonio-Nkondjio,Leslie Diane Nkahe,Parfait Awono-Ambene,Charles S Wondji,Benjamin D Menze,Flobert Njiokou

doi:10.1051/parasite/2021003

Abstract

In Cameroon, pyrethroid-only long-lasting insecticidal nets (LLINs) are still largely used for malaria control. The present study assessed the efficacy of such LLINs against a multiple-resistant population of the major malaria vector, Anopheles coluzzii, in the city of Yaoundé via a cone bioassay and release-recapture experimental hut trial. Susceptibility of field mosquitoes in Yaoundé to pyrethroids, DDT, carbamates and organophosphate insecticides was investigated using World Health Organization (WHO) bioassay tube tests. Mechanisms of insecticide resistance were characterised molecularly. Efficacy of unwashed PermaNet® 2.0 was evaluated against untreated control nets using a resistant colonised strain of An. coluzzii. Mortality, exophily and blood feeding inhibition were estimated. Field collected An. coluzzii displayed high resistance with mortality rates of 3.5% for propoxur (0.1%), 4.16% for DDT (4%), 26.9% for permethrin (0.75%), 50.8% for deltamethrin (0.05%), and 80% for bendiocarb (0.1%). High frequency of the 1014F west-Africa kdr allele was recorded in addition to the overexpression of several detoxification genes, such as Cyp6P3, Cyp6M2, Cyp9K1, Cyp6P4 Cyp6Z1 and GSTe2. A low mortality rate (23.2%) and high blood feeding inhibition rate (65%) were observed when resistant An. coluzzii were exposed to unwashed PermaNet® 2.0 net compared to control untreated net (p < 0.001). Furthermore, low personal protection (52.4%) was observed with the resistant strain, indicating reduction of efficacy. The study highlights the loss of efficacy of pyrethroid-only nets against mosquitoes exhibiting high insecticide resistance and suggests a switch to new generation bed nets to improve control of malaria vector populations in Yaoundé.

Highlights

Malaria is a major cause of morbidity and mortality in Sub-Saharan Africa, and in 2019 the disease was responsible for over 409,000 deaths and 229 million cases [60]
Female An. gambiae s.l. pre-exposed to piperonyl butoxide (PBO) showed an increase in susceptibility to both permethrin (p < 0.0001) and deltamethrin (p < 0.0001)
In Cote d’Ivoire, higher mortality rates were recorded when resistant An. gambiae populations were exposed to alpha-cypermethrin + PBO mixture long-lasting insecticidal nets (LLINs) compared to standard LLINs [38]

Summary

Introduction

Malaria is a major cause of morbidity and mortality in Sub-Saharan Africa, and in 2019 the disease was responsible for over 409,000 deaths and 229 million cases [60]. The rapid expansion of insecticide resistance resulting from the massive use of insecticides in both agriculture and public health, is considered a major threat limiting the performance of current control tools [41, 62] Several mechanisms such as target site resistance, notably knockdown resistance (kdr) [4, 9, 10], modified acetylcholinesterase Ace-1R [10, 19], the overexpression of detoxification genes [10, 19, 47, 53, 61], or cuticular resistance [7, 8, 10, 50, 63] have been reported to induce resistance to insecticides in vector populations. Recent studies on Anopheles funestus indicated that the expansion of pyrethroid resistance mediated by metabolic mechanisms such as monoxygenase P450 [32, 55] and glutathione s-transferase GST [30] was impacting the efficacy of nets

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