Skip to main content
Download PDF

Susceptibility of Anopheles gambiae from Côte d’Ivoire to insecticides used on insecticide-treated nets: evaluating the additional entomological impact of piperonyl butoxide and chlorfenapyr

Malaria Journal volume 19, Article number: 454 (2020) Cite this article

Abstract

Background

Pyrethroid-treated mosquito nets are currently the mainstay of vector control in Côte d’Ivoire. However, resistance to pyrethroids has been reported across the country, limiting options for insecticide resistance management due to the paucity of alternative insecticides. Two types of insecticide-treated nets (ITNs), ITNs with pyrethroids and the synergist piperonyl butoxide (PBO), and Interceptor®G2 nets, a net treated with a combination of chlorfenapyr and alpha-cypermethrin, are believed to help in the control of pyrethroid-resistant mosquitoes.

Methods

The susceptibility of Anopheles gambiae sensu lato (s.l.) to pyrethroid insecticides with and without pre-exposure to PBO as well as to chlorfenapyr was investigated in fifteen sites across the country. Susceptibility tests were conducted on 2- to 4-day old adult female An. gambiae s.l. reared from larval collections. The resistance status, intensity, and effects of PBO on mortality after exposure to different concentrations of deltamethrin, permethrin and alpha-cypermethrin were determined using WHO susceptibility test kits. In the absence of a WHO-recommended standard protocol for chlorfenapyr, two interim doses (100 and 200 µg/bottle) were used to test the susceptibility of mosquitoes using the CDC bottle assay method.

Results

Pre-exposure to PBO did not result in full restoration of susceptibility to any of the three pyrethroids for the An. gambiae s.l. populations from any of the sites surveyed. However, PBO pre-exposure did increase mortality for all three pyrethroids, particularly deltamethrin (from 4.4 to 48.9%). Anopheles gambiae s.l. from only one site (Bettie) were susceptible to chlorfenapyr at the dose of 100 µg active ingredient (a.i.)/bottle. At the dose of 200 µg (a.i.)/bottle, susceptibility was only recorded in 10 of the 15 sites.

Conclusion

Low mosquito mortality was found for pyrethroids alone, and while PBO increased mortality, it did not restore full susceptibility. The vector was not fully susceptible to chlorfenapyr in one third of the sites tested. However, vector susceptibility to chlorfenapyr seems to be considerably higher than for pyrethroids alone or with PBO. These data should be used cautiously when making ITN procurement decisions, noting that bioassays are conducted in controlled conditions and may not fully represent field efficacy where the host-seeking behaviours, which include free-flying activity are known to enhance pro-insecticide chlorfenapyr intoxication to mosquitoes.

Background

The recent malaria control success recorded in several malaria endemic countries is largely attributed to the scale up of vector control tools, particularly the implementation and high coverage of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) [1]. Pyrethroid insecticides have been used for several years both for ITNs and IRS because of their effectiveness in killing mosquitoes and also for their repellent properties, providing users additional personal protection and safety during sleeping hours [2, 3]. Due to their low cost, long residual activity and safety, pyrethroids remain the recommended insecticides for treating ITNs [4]. Unfortunately, the spread of target-site insensitivity and metabolic resistance mechanisms against pyrethroid insecticides occurring in malaria vectors are a threat to vector control and could lead to resurgence of malaria in endemic countries [5,6,7].

Resistance to all the insecticides previously used in public health for adult malaria vector control has been reported across Côte d’Ivoire [8], limiting the country’s malaria vector control toolkit. Côte d’Ivoire was the first West African country to report the knockdown resistance (kdr) mutation in the 1990s, before it was detected all over the continent [9, 10]. Moreover, due to the intense exposure of Anopheles mosquitoes to insecticides used in both agriculture and public health, An. gambiae s.l. have developed resistance in several parts of the country [8, 11, 12].

A first attempt to manage insecticide resistance using ITNs was the development of ITNs that incorporate a pyrethroid and a synergist, piperonyl butoxide (PBO), which has been shown to increase the mortality of malaria vectors with metabolic resistance involving mono-oxygenases. Currently, five ITNs types with PBO have been developed, all of which received WHO pre-qualification and are available on the market. Three of these are treated with a combination of PBO and deltamethrin (PermaNet 3.0, Tsara Plus, Tsara Boost), one with PBO and permethrin (Olyset Plus), and one with PBO and alpha-cypermethrin (Veeralin) [13,14,15]. The effectiveness of these ITNs in a given area depends on the extent of the involvement of metabolic resistance mediated by mono-oxygenase enzymes in vector populations. A countrywide distribution of such nets therefore requires baseline entomological studies to show the involvement of enzyme activities in pyrethroid resistance of An. gambiae s.l. and the effect of the synergist in restoring susceptibility of the targeted vector population to pyrethroids [16].

Recent research exploring other classes of insecticides identified chlorfenapyr-based tools as a promising option for vector control. Furthermore, WHO Pre-Qualification (WHO PQ) has approved chlorfenapyr-based nets and additional studies are ongoing under the UNITAID-funded New Nets Project to demonstrate the public health impact of those nets for wide use. The different mode of action of chlorfenapyr is expected to be effective in the presence of pyrethroid resistance developed by mosquitoes through several mutations [17, 18]. The oxidative removal of the N-ethoxymethyl group of the pro-insecticide chlorfenapyr leads to a toxic form of the molecule identified as CL 303268 which functions to uncouple oxidative phosphorylation and disrupt metabolic pathways of ATP production in mitochondria [19]. This molecule has low mammalian toxicity and is classified as a slightly hazardous insecticide by the WHO. Due to its novel mode of action, chlorfenapyr is unlikely to show any cross-resistance with standard neurotoxic insecticides as observed in Anopheles mosquitoes [20, 21]. Chlorfenapyr has been evaluated in laboratory bioassays and in experimental hut studies for ITNs in several countries including Côte d’Ivoire, Burkina Faso, Tanzania, and for both ITNs and IRS in Benin [22,23,24,25,26]. Results from those studies suggest that chlorfenapyr is promising as a new molecule for ITNs and IRS to control populations of pyrethroid-resistant malaria vectors [27, 28].

With regards to widespread resistance to the insecticides previously used and the aim of introducing new generation vector control tools in Côte d’Ivoire, ITNs with chlorfenapyr and PBO represent options to overcome and manage widespread resistance. The current study was undertaken within a countrywide insecticide resistance monitoring effort to support the National Malaria Control Programme (NMCP) in making vector control decisions in Côte d’Ivoire and also to contribute to the knowledge base for chlorfenapyr more broadly.

Methods

Study sites

Côte d’Ivoire is divided into four ecological zones including the forest zone in the South and West, the transitional zone in the Centre, the savanna zone and the Sudan savanna zone in the North. The climate in the southern forest zone is equatorial, with annual rainfall between 2100 mm and 2500 mm and subequatorial in the western forest with a range of average rainfall between 1600 and 2300 mm per year. In the central transitional zone of the country, the climate is tropical, with an average of 1200 mm rainfall per year. The climate is also tropical in the northern savanna and Sudan Savanah zone, with an annual average rainfall of 900 mm. Insecticide resistance surveys were carried out in fifteen sites distributed across the country, including Aboisso, Adzopé, and San Pedro in the South, Bouaké, Béoumi, Dabakala, Sakassou and Yamoussoukro in the Centre, Odienné in the North-West, Bouna and Nassian in the North-East, Daloa and Gagnoa in the west and Abengourou and Bettié in the East (Fig. 1). Of Those sites, ten represented the NMCP sentinel sites were all malaria control activities and impact were monitored all year round. The additional sites (Bettie, Gagnoa, Sakassou, Dabakala and Béoumi) were surveyed based on their malaria endemicity and targeted for indoor residual spraying site selection. Furthermore, the country has a history of two mass campaigns of pyrethroid-only long lasting insecticide treated net (LLIN) distributions conducted in 2014 and 2017.

Fig. 1
figure 1

Map of the study sites

Full size image

The study was conducted between June and September 2019. Anopheles gambiae s.l. larvae and pupae were collected from several urban and rural larval habitats in each site using the dipping method, pooled and reared to adulthood in a field laboratory at each site.

Insecticides and synergist

Papers impregnated with deltamethrin (0.05%, 0.25% and 0.5%), permethrin (0.75%, 3.75% and 7.5%), alpha-cypermethrin (0.05%, 0.25% and 0.5%) and PBO (4%) were obtained from University Sains Malaysia (USM).

Pre-weighed preparations of technical-grade active ingredient of chlorfenapyr (BASF Corporation USA, Batch N 2130H070HV) provided by the Centers for Disease Control and Prevention (CDC), Atlanta, were used to prepare 50 mL of two doses (100 µg (a.i)/bottle and 200 µg (a.i)/bottle) by adding the prescribed volume of acetone solvent. The solution obtained was vortexed to ensure that the solution was uniformly mixed. All insecticide solutions and papers were kept at 4 °C before and after each test.

Prior to the field susceptibility testing, two impregnated papers received were randomly selected from each box and tested against a laboratory-maintained susceptible strain of An. gambiae Kisumu to verify the effectiveness of the paper. Both chlorfenapyr solutions (100 µg (a.i.)/bottle and 200 µg (a.i.)/bottle) were also tested using the CDC bottle assay against An. gambiae Kisumu to check the efficacy on a susceptible population of mosquitoes.

WHO susceptibility test, intensity and synergist assays

Insecticide susceptibility tests were conducted using WHO tube tests on 2–4 day old adult female An. gambiae s.l. [29, 30]. The diagnostic concentrations of deltamethrin (0.05%), permethrin (0.75%), alpha-cypermethrin (0.05%) were tested alone and in combination with PBO concurrently in all sites. For the synergist assays, mosquitoes were pre-exposed to PBO for one hour before being exposed to the pyrethroid insecticides for one hour. Resistance intensity at five and ten times the diagnostic concentration of deltamethrin, permethrin and alpha-cypermethrin was also tested in each site using WHO susceptibility kits. Two tubes lined with silicone oil treated papers were set in parallel during each test and served as controls. The start and end temperatures during all tests were recorded at 9 sites, and Hobo data loggers (HOBO UX100-003, Onset Computer Co., Bourne, MA, USA) were used to track temperatures every 10 min in the laboratory in two sites (Beoumi and Sakassou) (Additional file 1).

CDC bottle assay with chlorfenapyr

Due to non-availability of a WHO recommended protocol for testing chlorfenapyr, two doses (100 µg (a.i.)/bottle and 200 µg (a.i.)/bottle) were selected based on a literature review [21, 27, 28, 31] and used to coat the CDC bottles. The bottles were coated following the protocol described by Brogdon et al. [32], with 1 mL of chlorfenapyr diluted in acetone at the concentration of 100 µg (a.i.)/bottle and 200 µg (a.i.)/bottle. The coated bottles were wrapped in aluminum foil and dried overnight at room temperature. A modified protocol was designed following the procedures described by Brogdon et al. [32]. Fifteen to 20 adult mosquitoes (2–4 days old) that emerged from field collected larvae were aspirated into 250 mL chlorfenapyr-coated Wheaton bottles for 1 h, after which the mosquitoes were released into a clean cage, aspirated back to paper cups and fed with 10% sugar solution. Mortality was recorded at 24, 48, and 72 h after exposure. Two bottles coated with acetone only were prepared similarly to serve as controls.

Species identification of the An. gambiae s.l. population

A subsample of about fifty An. gambiae s.l. mosquitoes was randomly selected among the population tested per site and processed for molecular identification of the species of the An. gambiae complex following the SINE PCR protocol described by Santolamazza et al. [33]. Additionally, the presence of knocked-down resistance (kdr)-West and East resistance mechanisms was characterized within each An. gambiae s.l. population using the Taqman protocol described by Bass et al. [34] and the presence of acetylcholinesterase (ace-1) gene was determined following the protocol described by Weill et al. [35].

Statistical analysis

Insecticide resistance status was defined following WHO criteria [27] with corrected mortality after 24 h for pyrethroids and 72 h for chlorfenapyr < 90% as confirmed resistance, between 90 and < 98% as possible resistance, and ≥ 98% as susceptible. Mortality was corrected using Abbott’s formula when the mortality of the control tubes was above 5% and less than 20%.

Corrected mortality of:

  • 98–100% at 5× the diagnostic dose indicates low resistance intensity

  • Less than 98% at 5× diagnostic dose implies testing the 10× diagnostic dose

  • 98–100% at 10× the diagnostic dose confirms a moderate resistance intensity.

  • Less than 98% at 10× the diagnostic doses indicates high resistance intensity.

For the synergist assays, an increase in the mortality after pre-exposure to PBO compared to the diagnostic dose of the insecticide alone indicates the involvement of enzymes such as P450s in the population tested. The mortality of mosquitoes exposed to PBO + pyrethroid was also compared with that of the insecticides alone and plotted using Graph Pad Prism 5 software. The total percentage mortality of all sites against each insecticide alone and those of the PBO + insecticides were analyzed and compared using a Chi-squared test with Stata 14 (Stata Corporation, College Station, Texas, USA).

Results

WHO susceptibility test, intensity and synergist assays

The An. gambiae s.l. population tested was primarily composed of Anopheles coluzzii (> 95%) in Abengourou, Adzopé, Béoumi, Bettié, Dabakala, Daloa, Gagnoa, Sakassou and San Pedro, while An. gambiae sensu stricto (s.s.) was the only member of the complex found in the country northern sites: Bouna, Nassian and Odienné. However, both species were in sympatry (≈ 50% each) in Aboisso, Bouaké and Yamoussoukro. Furthermore, high kdr-West resistance allele frequency was recorded in all the 15 sites ranging between 34% in Gagnoa and 97% in Odienné. The kdr-East was also observed in few sites but at a lower frequency compared to the kdr-West. The highest frequency was observed in Sakassou with 10% kdr-East resistance allele frequency. The ace-1 frequency was relatively high in eight of the fifteen sites (between 28% in Odienné to 65% in Gagnoa) (Fig. 2).

Fig. 2
figure 2

Distribution and frequency of the knocked-down resistance (kdr) West, kdr-East and acetylcholinesterase (ace-1) within the An. gambiae s.l. population of each site

Full size image

Full susceptibility (100% mortality) was recorded for all insecticides tested against An. gambiae Kisumu and no sign of compromised quality and/or efficacy of the insecticide impregnated papers and the chlorfenapyr-coated bottles were observed.

The start temperatures in the 9 sites where start and end temperatures were recorded had a mean of 25.4 °C (minimum 23.0 °C, maximum 28.2 °C) at the start of tests and 25.2 °C at the end of tests (minimum 23.8 °C, maximum 26.8 °C). During the tests with chlorfenapyr, the range was smaller, with mean start temperatures of 25.6 °C (minimum 24.0 °C, maximum 26.7 °C) and end temperatures of 25.2 °C (minimum 24.0 °C, maximum 26.0 °C). As would be expected since the loggers measured the temperature every 10 min, the Hobo loggers picked up a larger variation in temperature, with laboratories ranging from 22.9 to 28.3 °C (Beoumi) and 24.1 °C to 28.4 °C (Sakassou).

Resistance of An. gambiae s.l. mosquitoes to pyrethroids at diagnostic doses was observed in all fifteen sites surveyed. The mean mortality rate (all sites) was below 10% for all three pyrethroids: 4.4% (± 0.8 standard error (SE) for deltamethrin, 3.1% (± 0.6 SE) for permethrin and 3.4% (± 0.9 SE) for alpha-cypermethrin (Figs. 3, 4, 5). Additionally, high pyrethroid resistance intensity was observed in all sites with survival recorded at 10× the diagnostic doses (DD) of deltamethrin (between 27.8% mortality at Dabakala and 79.5% at Beoumi), permethrin (between 40.7% mortality at Daloa and 95.9% at Beoumi) and alpha-cypermethrin (between 13.5% mortality at Yamoussoukro and 80.2% at Odienné). Only An. gambiae s.l. collected from Odienné (100% mortality at 10× DD) and Nassian (98.9% mortality at 10× DD) showed moderate resistance intensity to permethrin.

Fig. 3
figure 3

WHO susceptibility and intensity assays of deltamethrin against An. gambiae s.l. of the different sites surveyed. Error bars represent the standard errors at the Y axis and the red line represents the susceptibility treshold

Full size image
Fig. 4
figure 4

WHO susceptibility and intensity assays of permethrin against An. gambiae s.l. of the different sites surveyed. Error bars represent the standard errors at the Y axis and the red line represents the susceptibility treshold

Full size image
Fig. 5
figure 5

WHO susceptibility and intensity assays of alpha-cypermethrin against An. gambiae s.l. of the different sites surveyed. Error bars represent the standard errors at the Y axis and the red line represents the susceptibility treshold

Full size image

When all sites were considered together, synergist assays using PBO pre-exposure yielded statistically significant increases in the mean mortality for all three pyrethroids (p < 0.0001) (Fig. 6; Additional file 2). Average permethrin mortality increased from 2.9% when tested alone to 26% mortality with PBO pre-exposure. Deltamethrin mortality was 4.3% mortality without PBO and 47.7% mortality with PBO pre-exposure. Alpha-cypermethrin mortality was 3.3% without PBO and 33.7% with PBO pre-exposure (Additional file 3).

Fig. 6
figure 6

Comparative percentage increment in susceptibility of An. gambiae s.l. using the synergist piperonyl butoxide (PBO) + pyrethroids in relation to pyrethroids alone across all sites surveyed. Significant increment in susceptibility was observed with the addition of PBO (p < 0.001) for all three pyrethroids

Full size image

Chlorfenapyr CDC bottle assay

Susceptibility (98–100%) was recorded for chlorfenapyr after 24 h and 48 h delayed mortality for the dose of 200 µg/bottle and 100 µg/bottle, respectively, when tested against the An. gambiae Kisumu strain.

Anopheles gambiae s.l. from only one out of 15 sites (Bettie) recorded susceptibility (98.8% mortality) when exposed to the 100 µg/bottle dose of chlorfenapyr (Fig. 7). The 200 µg/bottle dose yielded more than 98% mortality in ten out of 15 sites. Mortality ranging between 87.3% in Sakassou to 94.8% in Nassian was observed at the dose of 200 µg/bottle in Bouake, Gagnoa, Nassian, Sakassou, and San Pedro (Fig. 8) (Additional file 4).

Fig. 7
figure 7

CDC bottle assay using chlorfenapyr 100 µg/bottle against An. gambiae s.l. of the different sites surveyed. Error bars represent the standard errors at the Y axis and the red line represents the susceptibility treshold

Full size image
Fig. 8
figure 8

CDC bottle assay using chlorfenapyr 200 µg/bottle against An. gambiae s.l. of the different sites surveyed. Error bars represent the standard errors at the Y axis and the red line represents the susceptibility treshold

Full size image

Discussion

Resistance of An. gambiae s.l. mosquitoes to pyrethroids observed in this study is consistent with the previously described trends in Côte d’Ivoire involving various and high insecticide resistance mechanisms such as the kdr-West and East and the ace-1 mutations [8, 11, 12, 36, 37]. Testing the intensity of the resistance from 15 sites showed that resistance intensity to all three pyrethroid insecticides is high. This presents a challenge for malaria control as it limits the country’s options for insecticide-based vector control interventions. The level of resistance observed could be attributed to the different applications of insecticide in the country, either for agriculture or public health. Agriculture accounts for 24% of GDP in Côte d’Ivoire, one of the largest producers and exporters of coffee, cocoa, cashew, and palm oil worldwide. A recent survey by the ministry of agriculture revealed that more than 20,000 tons of chemicals including pesticides and insecticides were applied in the country in 2018 for agricultural purposes including 40% of this amount entering illegally [38]. This likely contributed to the increasing resistance of malaria vectors to insecticides commonly used for insect control in general and malaria vector control specifically [36, 37, 39]. In Côte d’Ivoire, the two major malaria vectors include An. gambiae and An. coluzzii [40]. Both species generally breed in fresh water pools resulting from human activities such as irrigated rice fields and vegetable gardens, which are often treated with insecticides [36, 37, 39, 41]. As described by Chouaibou et al. [42], agricultural pesticides contain several insecticide molecules and particularly pyrethroids and carbamates, which contribute to the increased and widespread resistance of the vectors [39]. Furthermore, studies conducted in Western and Eastern Africa have shown a significant increase in the frequency of genes associated with pyrethroid resistance immediately following the implementation of an ITN campaign [7]. Moreover, the National Strategic Plan (NSP) developed in 2018 by the Côte d’Ivoire National Malaria Control Programme (NMCP) prioritized universal ITN coverage in households across the country through mass distribution campaign of pyrethroid-only ITNs.

In this study, pre-exposure to PBO before the different pyrethroids tested showed statistically significant but still insufficient increases in the mortality of the An. gambiae s.l. populations. These results would support the use of PBO-treated vector control tools in select areas where significant reversal of resistance was observed after pre-exposure to PBO. In some locations, PBO has resulted in increased mortality of even highly resistant mosquito populations [43]. Out of several combinations of PBO ITNs, combinations with the type II pyrethroids (deltamethrin and alpha-cypermethrin) showed higher performance than those with the type I pyrethroid (permethrin), consistent with several other studies comparing the different types of PBO ITNs [44, 45]. These data could inform the selection and stratification of the PBO ITNs for resistance management in Côte d’Ivoire.

Higher mortality of mosquitoes was observed against chlorfenapyr particularly in areas of probable metabolic resistance where higher mortality was noted after pre-exposure of the mosquitoes to PBO before the different pyrethroids. It is known that significant increase in mortality after exposure to PBO indicates the involvement of P450 enzymes in the insecticide resistance of the vectors. The trends observed were consistent with previous observations, when assessing the lethality of chlorfenapyr in areas of high metabolic resistance in Aedes aegypti after mosquitoes are exposed or not to PBO [17].

Chlorfenapyr is a protoxin requiring activation, via cytochrome P450 monooxygenases, to exert its toxic effects, via uncoupling of oxidative phosphorylation [17, 19]. The expression in An. gambiae s.l. of some cytochrome P450s involved in oxidative metabolism are under circadian control and more strongly expressed at night when Anopheles flight and host-seeking activity are higher [46, 47]. Such a model could suggest that exposure at night could likely produce higher mortality results compared to what was observed using traditional testing methods. The supposition that laboratory-based exposures to technical grade active ingredient or any other formulation where behaviours are excluded, likely negates attributes of oxidative uncoupling by chlorfenapyr when compared to host-seeking behaviours which include free-flying physiologically heightened states known to enhance pro-insecticide chlorfenapyr intoxication to mosquitoes as demonstrated by Oxborough et al. [31].

Furthermore, previous work showed that testing completed during the night induces significantly greater mortality than daytime bioassays, indicating the possibility of higher effectiveness of chlorfenapyr-based ITNs such as Interceptor® G2 since the peak biting hours of the vectors are typically late in the night [31]. Moreover, several studies are still ongoing to understand and delineate the appropriate diagnostic doses and times for testing chlorfenapyr susceptibility [31, 48, 49]. This study will therefore contribute to the evidence base for supporting the determination of an appropriate diagnostic dose. With regards to the data generated, in ten out of 15 sites where the tests were conducted, 98% or greater mortality was recorded at the dose of 200 µg/bottle against An. gambiae s.l., indicating that chlorfenapyr could be considered as an option to manage the resistant population of malaria vectors in Côte d’Ivoire, where resistance has continuously increased over the past several decades.

Several trials and studies have been conducted on the Interceptor® G2 net. As described by Bayili et al., Camara et al. [22, 23] and Ngufor et al. [26] chlorfenapyr-treated nets evaluated in several areas with documented pyrethroid resistance have been proven effective for controlling pyrethroid-resistant malaria vectors and could contribute to malaria control decision-making and insecticide resistance management in Côte d’Ivoire.

Though it yielded important findings, this study had limitations. There is no standardized and WHO approved test protocol available for chlorfenapyr. The best available information was used to determine the concentration of insecticide tested, exposure and holding period, and test conditions and interpretation of the result. The protocol might be optimized by conducting susceptibility tests at different temperatures, comparing tests results conducted during day light versus night, or putting the mosquitoes in dark room during exposure period. Until such standardized protocol is developed for guidance, the data showing reduced susceptibility of An. gambiae s.l. to chlorfenapyr shall be interpreted with caution applying it only to specific study conditions. Despite this limitation, the information gathered could contribute to informing vector control programming in Côte d’Ivoire.

Conclusion

As resistance to all pyrethroid insecticides is very high across the country, new tools such as chlorfenapyr- and PBO-combination ITNs may be appropriate for Côte d’Ivoire. This study demonstrated the relative increase in effectiveness observed when exposing the pyrethroid-resistant mosquitoes to either PBO in combination with pyrethroids or to chlorfenapyr. Both options represent avenues for many African country NMCPs to develop insecticide resistance management strategies. In Côte d’Ivoire, Interceptor® G2, a chlorfenapyr- and alpha-cypermethrin-based ITN could therefore be considered for a stratified distribution campaign in addition to PBO ITNs. The data gathered across the country within this study could also support the determination of the diagnostic concentration for testing the susceptibility status of An. gambiae s.l. against chlorfenapyr while the molecule is still being tested for appropriate concentrations in ITNs and IRS.

Availability of data and materials

All data generated or analyzed during this study are included in this published article and its Additional files.

Abbreviations

Ace-1:

Acetylcholinesterase

BASF:

Badische Anilin- & Soda-Fabrik

CDC:

Centers for Disease Control and Prevention

IRS:

Indoor residual spraying

ITN:

Insecticide-treated net

Kdr:

Knocked-down resistance

NMCP:

National Malaria Control Programme

NSP:

National Strategic Plan

PBO:

Piperonyl butoxide

PCR:

Polymerase Chain Reaction

PQ:

Prequalification

SE:

Standard Error

SINE:

Short Interspersed Element

USM:

University Sains of Malaysia

WHO:

World Health Organization

References

  1. Bhatt S, Weiss DJ, Cameron E, Bisanzio D, Mappin B, Dalrymple U, et al. The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015. Nature. 2015;26:207–11.

    Article  Google Scholar 

  2. Lindsay SW, Snow RW, Broomfield GL, Janneh MS, Wirtz RA, Greenwood BM. Impact of permethrin-treated bednets on malaria transmission by the Anopheles gambiae complex in The Gambia. Med Vet Entomol. 1989;3:263–71.

    Article  CAS  Google Scholar 

  3. Mosha FW, Lyimo IN, Oxborough RM, Matowo J, Malima R, Feston E, et al. Comparative efficacies of permethrin-, deltamethrin- and alpha-cypermethrin-treated nets, against Anopheles arabiensis and Culex quinquefasciatus in northern Tanzania. Ann Trop Med Parasitol. 2008;102:367–76.

    Article  CAS  Google Scholar 

  4. Zaim M, Aitio A, Nakashima N. Safety of pyrethroid-treated mosquito nets. Med Vet Entomol. 2000;14:1–5.

    Article  CAS  Google Scholar 

  5. Ranson H, Jensen B, Wang X, Prapanthadara L, Hemingway J, Collins FH. Genetic mapping of two loci affecting DDT resistance in the malaria vector Anopheles gambiae. Insect Mol Biol. 2000;9:499–507.

    Article  CAS  Google Scholar 

  6. Ranson H, Lissenden N. Insecticide resistance in African Anopheles mosquitoes: a worsening situation that needs urgent action to maintain malaria control. Trends Parasitol. 2016;32:187–96.

    Article  CAS  Google Scholar 

  7. Ranson H, N’Guessan R, Lines J, Moiroux N, Nkuni Z, Corbel V. Pyrethroid resistance in African anopheline mosquitoes: what are the implications for malaria control? Trends Parasitol. 2011;27:91–8.

    Article  CAS  Google Scholar 

  8. Edi CV, Koudou BG, Jones CM, Weetman D, Ranson H. Multiple-insecticide resistance in Anopheles gambiae mosquitoes, southern Côte d’Ivoire. Emerg Infect Dis. 2012;18:1508–11.

    Article  CAS  Google Scholar 

  9. Chandre F, Darriet F, Manguin S, Brengues C, Carnevale P, Guillet P. Pyrethroid cross resistance spectrum among populations of Anopheles gambiae s.s. from Côte d’Ivoire. J Am Mosq Control Assoc. 1999;15:53–9.

    CAS  PubMed  Google Scholar 

  10. Chandre F, Manguin S, Brengues C, Dossou Yovo J, Darriet F, Diabate A, et al. Current distribution of a pyrethroid resistance gene (kdr) in Anopheles gambiae complex from west Africa and further evidence for reproductive isolation of the Mopti form. Parassitologia. 1999;41:319–22.

    CAS  PubMed  Google Scholar 

  11. Camara S, Koffi AA, Ahoua Alou LP, Koffi K, Kabran JK, Kone A, et al. Mapping insecticide resistance in Anopheles gambiae (s.l.) from Côte d’Ivoire. Parasites Vectors. 2018;11:19.

    Article  Google Scholar 

  12. Edi CA, Koudou BG, Bellai L, Adja AM, Chouaibou M, Bonfoh B, et al. Long-term trends in Anopheles gambiae insecticide resistance in Côte d’Ivoire. Parasites Vectors. 2014;7:500.

    PubMed  PubMed Central  Google Scholar 

  13. WHO. World Health Organization: report of the 12th WHOPES Working Group meeting—review of Bioflash® GR, Permanet® 2.0, Permanet® 3.0, Permanet® 2.5, Lambdacyhalothrin LN. World Health Organization, 2009. WHO/HTM/NTD/WHOPES/2009;1:8–11.

  14. WHO. World Health Organization: report of the fifteenth WHOPES working group meeting: WHO/HQ, Geneva, 18–22 June 2012: review of Olyset Plus, Interceptor LN, Malathion 440EW, Vectobac GR, Geneva, Switzerland. Pesticide Evaluation Scheme, Working Group Meeting; 2012.

  15. WHO. Report of the nineteenth WHOPES working group meeting: WHO/HQ, Geneva, 8–11 February 2016. Review of Veeralin LN, VectoMax GR, Bactivec SC. WHO/Department of control of neglected tropical diseases, 2016. WHO/HTM/NTD/WHOPES/2016;2:92.

  16. WHO. Conditions for use of long-lasting insecticidal nets treated with a pyrethroid and piperonyl butoxide. Geneva: WHO Evidence Review Group Meeting report; 2015.

  17. Paul A, Harrington LC, Scott JG. Evaluation of novel insecticides for control of dengue vector Aedes aegypti (Diptera: Culicidae). J Med Entomol. 2006;43:55–60.

    Article  CAS  Google Scholar 

  18. Read AF, Lynch PA, Thomas MB. How to make evolution-proof insecticides for malaria control. PLoS Biol. 2009;7:e1000058.

    Article  Google Scholar 

  19. Black BC, Hollingworth RM, Ahammadsahib KI, Kukel CD, Donovan S. Insecticidal action and mitochondrial uncoupling activity of AC-303,630 and related halogenated pyrroles. Pestic Biochem Physiol. 1994;50:115–28.

    Article  CAS  Google Scholar 

  20. N’Guessan R, Boko P, Odjo A, Knols B, Akogbeto M, Rowland M. Control of pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes with chlorfenapyr in Benin. Trop Med Int Health. 2009;14:389–95.

    Article  CAS  Google Scholar 

  21. Oliver SV, Kaiser ML, Wood OR, Coetzee M, Rowland M, Brooke BD. Evaluation of the pyrrole insecticide chlorfenapyr against pyrethroid resistant and susceptible Anopheles funestus (Diptera: Culicidae). Trop Med Int Health. 2010;15:127–31.

    CAS  PubMed  Google Scholar 

  22. Bayili K, N’do S, Namountougou M, Sanou R, Ouattara A, Dabiré RK, et al. Evaluation of efficacy of Interceptor(®) G2, a long-lasting insecticide net coated with a mixture of chlorfenapyr and alpha-cypermethrin, against pyrethroid resistant Anopheles gambiae s.l. in Burkina Faso. Malar J. 2017;16:190.

    Article  Google Scholar 

  23. Camara S, Ahoua Alou LP, Koffi AA, Clegban YCM, Kabran JP, Koffi FM, et al. Efficacy of Interceptor(®) G2, a new long-lasting insecticidal net against wild pyrethroid-resistant Anopheles gambiae s.s. from Côte d’Ivoire: a semi-field trial. Parasite. 2018;25:42.

    Article  Google Scholar 

  24. N’Guessan R, Ngufor C, Kudom AA, Boko P, Odjo A, Malone D, et al. Mosquito nets treated with a mixture of chlorfenapyr and alphacypermethrin control pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes in West Africa. PLoS ONE. 2014;9:e87710.

    Article  Google Scholar 

  25. N’Guessan R, Odjo A, Ngufor C, Malone D, Rowland M. A chlorfenapyr mixture net Interceptor(®) G2 shows high efficacy and wash durability against resistant mosquitoes in West Africa. PLoS ONE. 2016;11:e0165925.

    Article  Google Scholar 

  26. Ngufor C, N’Guessan R, Boko P, Odjo A, Vigninou E, Asidi A, et al. Combining indoor residual spraying with chlorfenapyr and long-lasting insecticidal bed nets for improved control of pyrethroid-resistant Anopheles gambiae: an experimental hut trial in Benin. Malar J. 2011;10:343.

    Article  CAS  Google Scholar 

  27. Raghavendra K, Barik TK, Bhatt RM, Srivastava HC, Sreehari U, Dash AP. Evaluation of the pyrrole insecticide chlorfenapyr for the control of Culex quinquefasciatus Say. Acta Trop. 2011;118:50–5.

    Article  CAS  Google Scholar 

  28. Raghavendra K, Barik TK, Sharma P, Bhatt RM, Srivastava HC, Sreehari U, et al. Chlorfenapyr: a new insecticide with novel mode of action can control pyrethroid resistant malaria vectors. Malar J. 2011;10:16.

    Article  Google Scholar 

  29. WHO. Test procedures for insecticide resistance monitoring in malaria vectors mosquitoess. Geneva: World Health Organization. 2013;40.

  30. WHO. Test procedures for insecticide resistance monitoring in malaria vectors, bio-efficacy and persistence of insecticide on treated surfaces. Geneva: World Health Organization; 1998. WHO/CDS/CPC/MAL/98.12.

  31. Oxborough RM, N’Guessan R, Jones R, Kitau J, Ngufor C, Malone D, et al. The activity of the pyrrole insecticide chlorfenapyr in mosquito bioassay: towards a more rational testing and screening of non-neurotoxic insecticides for malaria vector control. Malar J. 2015;14:124.

    Article  Google Scholar 

  32. CDC. Centers for Disease Control and Prevention. Guidelines for evaluating insecticide resistance in vectors using the CDC bottle bioassay. CDC Atlanta; 2010.

  33. Santolamazza F, Mancini E, Simard F, Qi Y, Tu Z, della Torre A. Insertion polymorphisms of SINE200 retrotransposons within speciation islands of Anopheles gambiae molecular forms. Malar J. 2008;7:163.

    Article  Google Scholar 

  34. Bass C, Nikou D, Donnelly MJ, Williamson MS, Ranson H, Ball A, et al. Detection of knockdown resistance (kdr) mutations in Anopheles gambiae: a comparison of two new high-throughput assays with existing methods. Malar J. 2007;6:111.

    Article  Google Scholar 

  35. Weill M, Malcolm C, Chandre F, Mogensen K, Berthomieu A, Marquine M, et al. The unique mutation in ace-1 giving high insecticide resistance is easily detectable in mosquito vectors. Insect Mol Biol. 2004;13:1–7.

    Article  CAS  Google Scholar 

  36. Chouaibou MS, Fodjo BK, Fokou G, Allassane OF, Koudou BG, David JP, et al. Influence of the agrochemicals used for rice and vegetable cultivation on insecticide resistance in malaria vectors in southern Côte d’Ivoire. Malar J. 2016;15:426.

    Article  Google Scholar 

  37. Fodjo BK, Koudou BG, Tia E, Saric J, N’Dri PB, Zoh MG, et al. Insecticides resistance status of An gambiae in areas of varying agrochemical use in Côte d’Ivoire. Biomed Res Int. 2018. https://0-doi-org.brum.beds.ac.uk/10.1155/2018/2874160.

    Article  PubMed  PubMed Central  Google Scholar 

  38. MADR. Programme de transformation de l'agriculture en Afrique de l'Ouest (PTAAO), Plan de gestion des pestes (PGP). Rapport final. 2018. p. 1–93.

  39. Chabi J, Eziefule MC, Pwalia R, Joannides J, Obuobi D, Amlalo G, et al. Impact of urban agriculture on the species distribution and insecticide resistance profile of Anopheles gambiae s.s. and Anopheles coluzzii in Accra Metropolis, Ghana. Adv Entomol. 2018;6:198–211.

    Article  Google Scholar 

  40. Tia E, Chouaibou M, Gbalegba CNG, Boby AMO, Kone M, Kadjo AK. Distribution of species and kdr gene frequency among Anopheles gambiae s.s. and Anopheles coluzzii populations in five agricultural sites in Côte d’Ivoire. Bull Soc Pathol Exot. 2017;110:130–4 (In French).

    Article  CAS  Google Scholar 

  41. N’Guessan R, Darriet F, Guillet P, Carnevale P, Traore-Lamizana M, Corbel V, et al. Resistance to carbosulfan in Anopheles gambiae from Ivory Coast, based on reduced sensitivity of acetylcholinesterase. Med Vet Entomol. 2003;17:19–25.

    Article  CAS  Google Scholar 

  42. Mouhamadou CS, de Souza SS, Fodjo BK, Zoh MG, Bli NK, Koudou BG. Evidence of insecticide resistance selection in wild Anopheles coluzzii mosquitoes due to agricultural pesticide use. Infect Dis Poverty. 2019;8:64.

    Article  Google Scholar 

  43. Dadzie SK, Chabi J, Asafu-Adjaye A, Owusu-Akrofi O, Baffoe-Wilmot A, Malm K, et al. Evaluation of piperonyl butoxide in enhancing the efficacy of pyrethroid insecticides against resistant Anopheles gambiae s.l. in Ghana. Malar J. 2017;16:342.

    Article  Google Scholar 

  44. Corbel V, Chabi J, Dabire RK, Etang J, Nwane P, Pigeon O, et al. Field efficacy of a new mosaic long-lasting mosquito net (PermaNet 3.0) against pyrethroid-resistant malaria vectors: a multi centre study in Western and Central Africa. Malar J. 2010;9:113.

    Article  Google Scholar 

  45. Ketoh GK, Ahadji-Dabla KM, Chabi J, Amoudji AD, Apetogbo GY, Awokou F, et al. Efficacy of two PBO long lasting insecticidal nets against natural populations of Anopheles gambiae s.l. in experimental huts, Kolokope, Togo. PLoS ONE. 2018;13:e0192492.

    Article  Google Scholar 

  46. Balmert NJ, Rund SS, Ghazi JP, Zhou P, Duffield GE. Time-of-day specific changes in metabolic detoxification and insecticide resistance in the malaria mosquito Anopheles gambiae. J Insect Physiol. 2014;64:30–9.

    Article  CAS  Google Scholar 

  47. Jones MD, Gubbins SJ, Cubbin CM. Circadian flight activity in four sibling species of the Anopheles gambiae complex (Diptera, Culicidae). Bull Entomol Res. 1974;64:241–6.

    Article  Google Scholar 

  48. Agumba S, Gimnig JE, Ogonda L, Ombok M, Kosgei J, Munga S, et al. Diagnostic dose determination and efficacy of chlorfenapyr and clothianidin insecticides against Anopheles malaria vector populations of western Kenya. Malar J. 2019;18:243.

    Article  Google Scholar 

  49. Dagg K, Irish S, Wiegand RE, Shililu J, Yewhalaw D, Messenger LA. Evaluation of toxicity of clothianidin (neonicotinoid) and chlorfenapyr (pyrrole) insecticides and cross-resistance to other public health insecticides in Anopheles arabiensis from Ethiopia. Malar J. 2019;18:49.

    Article  Google Scholar 

Download references

Acknowledgements

We gratefully acknowledge the contribution of all the students and technicians of the Swiss Centre of Scientific Research (SCSR), Medical and Veterinary Entomology Centre (MVEC), National Institute of Public Hygiene (NIPH) and Pierre Richet Institute (PRI) who contributed to the field susceptibility testing. Special thanks to the NMCP Côte d’Ivoire for facilitating and participating on field data collections.

Funding

This study was supported by the United States President’s Malaria Initiative through the United States Agency for International Development (USAID) Abt Associates/VectorLink Project. The findings and conclusions expressed herein are those of the author(s) and do not necessarily represent the official position of USAID, PMI, or the Centers for Disease Control and Prevention (CDC).

Author information

Authors and Affiliations

  1. PMI VectorLink project, Abidjan, Côte d’Ivoire

    Bernard L. Kouassi, Ndombour G. Cissé & Joseph Chabi

  2. Swiss Center of Scientific Research in Côte d’Ivoire, Abidjan, Côte d’Ivoire

    Constant Edi & Allassane F. Ouattara

  3. Centre of Veterinary and Medical Entomology, Abidjan, Côte d’Ivoire

    Emmanuel Tia

  4. National Institute of Public Hygiene, Abidjan, Côte d’Ivoire

    Lucien Y. Konan

  5. National Institute of Public Health/Pierre Richet Institute, Bouake, Côte d’Ivoire

    Maurice A. Akré & Alphonsine A. Koffi

  6. National Malaria Control Programme, Abidjan, Côte d’Ivoire

    Antoine Mea Tanoh & McKenzie Andre

  7. U.S. President’s Malaria Initiative, USAID, Abidjan, Côte d’Ivoire

    Pascal Zinzindohoue & Blaise Kouadio

  8. U.S. President’s Malaria Initiative, Entomology Branch, U.S. Centers for Disease Control and Prevention, Atlanta, GA, USA

    Seth R. Irish

  9. U.S. President’s Malaria Initiative, USAID, Washington, DC, USA

    Jennifer Armistead

  10. PMI VectorLink Project, Washington, DC, USA

    Dereje Dengela & Cecilia Flatley

Authors
  1. Bernard L. Kouassi
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Constant Edi
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Emmanuel Tia
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Lucien Y. Konan
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Maurice A. Akré
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Alphonsine A. Koffi
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Allassane F. Ouattara
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Antoine Mea Tanoh
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Pascal Zinzindohoue
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Blaise Kouadio
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. McKenzie Andre
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Seth R. Irish
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Jennifer Armistead
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Dereje Dengela
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Ndombour G. Cissé
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. Cecilia Flatley
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. Joseph Chabi
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

BLK, CE and JC participated on the activity planning, supervision and drafted the manuscript, ET, LYK, AAK, MAA and AFO supported and supervised the data collection, ATM, PZ, BK, MKA, SRI, JA, DD, NGC and CF reviewed the manuscript for improvement. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Joseph Chabi.

Ethics declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Information

Additional file 1

WHO susceptibility tests and CDC bottle assays testing conditions (Temperature and humidity) of the different sites surveyed.

Additional file 2

Insecticide susceptibility test and resistance intensity data and graphs.

Additional file 3

Synergist assays using pyrethroid insecticides and piperonyl butoxide data.

Additional file 4

Chlorfenapyr assay test data and graphs.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Kouassi, B.L., Edi, C., Tia, E. et al. Susceptibility of Anopheles gambiae from Côte d’Ivoire to insecticides used on insecticide-treated nets: evaluating the additional entomological impact of piperonyl butoxide and chlorfenapyr. Malar J 19, 454 (2020). https://0-doi-org.brum.beds.ac.uk/10.1186/s12936-020-03523-y

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://0-doi-org.brum.beds.ac.uk/10.1186/s12936-020-03523-y

Keywords

Malaria Journal

ISSN: 1475-2875

Contact us