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

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.

Molecular Drivers of Multiple and Elevated Resistance to Insecticides in a Population of the Malaria Vector Anopheles gambiae in Agriculture Hotspot of West Cameroon

“…Many studies reported escalation in resistance to pyrethroids across the country in An. coluzzii [ 29 , 41 ] and An. funestus [ 42 ] but it is the first time resistance have been noticed for organophosphates.…”

Population knowledge, attitudes and practices towards malaria prevention in the locality of Makenene, Centre-Cameroon

“…Other means of protection, such as insecticide sprays, mosquito coils and screens on windows were also used by the population. Previous studies have shown that the use of insecticide sprays, especially in purely agricultural areas, would increase the rate of resistance in the mosquito population [ 4 , 28 , 46 ] and would, therefore, reduce the bio-efficacy of LLINs [ 47 ].…”

Pyrethroid Resistance Situation across Different Eco-Epidemiological Settings in Cameroon

“…Functional expression analysis in An. gambiae indicated that Cyp9k1 was able to metabolize deltamethrin, as well as pyriproxyfen [ 39 , 40 ]. Cyp6p4, Cyp6z1, Cyp6p3 and Cyp6m2 were also found to be upregulated in at least one population.…”

“…Cyp6p4, Cyp6z1, Cyp6p3 and Cyp6m2 were also found to be upregulated in at least one population. Cyp6p4, Cyp6m2 and Cyp6p3 have been shown to metabolize pyrethroids (permethrin, etofenprox, deltamethrin) [ 36 , 37 , 39 ]. Cyp6z1 have been reported to metabolize DDT in An.…”

“…Cyp6z1 have been reported to metabolize DDT in An. gambiae [ 39 ]. Cyp4g16, which was found to be upregulated in Tibati, is a functional oxidative decarboxylase gene known to catalyze the last step of epicuticular hydrocarbon biosynthesis and could contribute to insecticide resistance via the enriched synthesis of CHCs, thus reducing pyrethroid uptake [ 41 , 42 , 43 ].…”