The objective of this study is to provide data on insecticide resistance for decision-making on resistance management programmes in Togo.
The susceptibility status of Anopheles gambiae (SL) to insecticides used in public health was assessed using the WHO in vitro test protocol. Bioassays for pyrethroid resistance were conducted according to CDC bottle test protocols. Detoxifying enzyme activities were tested using the synergists piperonyl butoxide, SSS-phosphorothioate, and ethacrine. Species-specific identification and genotyping of the kdr mutation in Anopheles gambiae SL using PCR technology.
Local populations of Anopheles gambiae s.l. showed complete susceptibility to pirimiphos-methyl at Lomé, Kowie, Aniye and Kpeletutu. Mortality was 90% at Bayda, indicating probable resistance to pirimiphos-methyl. Resistance to DDT, benzodicarb and propoxur was recorded at all sites. High levels of resistance to pyrethroids were recorded, with oxidases, esterases and glutathione-s-transferases being the detoxifying enzymes responsible for resistance, according to synergistic tests. The main species detected were Anopheles gambiae (ss) and Anopheles cruzi. High frequencies of kdr L1014F and low frequencies of kdr L1014S alleles were detected at all sites.
This study demonstrates the need for additional tools to strengthen existing insecticide-based malaria control interventions (IRS and LLIN).
The use of insecticides is an important component of malaria vector control programmes in Africa [1]. However, the emergence of resistance to the main classes of insecticides used in bednet treatment and indoor residual spraying (IRS) requires us to reconsider the use of these products and the management of vector resistance [2]. The emergence of drug resistance has been reported in various countries in West Africa including Benin, Burkina Faso, Mali [3, 4, 5] and especially Togo [6, 7]. Recent studies have shown that the use of synergists and combinations of insecticides increases the susceptibility of malaria vectors in areas with high resistance to pyrethroids [8, 9]. To maintain the sustainability of control strategies, systematic integration of resistance management into any vector control policy should be considered [2]. Any country should support the implementation of resistance management programmes through resistance detection [10]. According to World Health Organization (WHO) recommendations [10], resistance management involves the implementation of a three-step approach including (1) assessment of insecticide susceptibility status of vectors, (2) characterization of resistance intensity, and (3) assessment of physiological mechanisms, with particular attention to the efficacy of the synergist piperonyl butoxide (PBO). In Togo, the first step, assessment of insecticide susceptibility status of malaria vectors, is carried out every 2–3 years in sentinel sites of the National Malaria Control Programme (NMCP). The resistance strength and efficacy of the last two steps (i.e., the potentiators piperonyl butoxide (PBO), S,S,S-tributyl trisulfate phosphate (DEF), and ethacrynic acid (EA)) have not been extensively studied.
The aim of this study is to address these three aspects and provide NMCP with reliable data to make decisions on resistance management in Togo.
This study was conducted from June to September 2021 at selected NMCP sentinel sites in three health districts in southern Togo (Figure 1). Five NMCP monitoring sites were selected for monitoring based on their geographical (different sanitary zones) and environmental characteristics (abundance of vectors, permanent larval breeding sites): Lomé, Bayda, Kowie, Anyère and Kpeletoutou (Table 1).
This study shows that local Anopheles gambiae mosquito populations in southern Togo are resistant to several major public health insecticides, with the exception of pirimiphos-methyl. High levels of pyrethroid resistance were observed at the study site, possibly associated with detoxifying enzymes (oxidases, esterases and glutathione-s-transferases). The kdr L1014F mutation was detected in the two sister species Anopheles gambiae ss and Anopheles kruzi with variable but high allele frequencies (>0.50), whereas the kdr L1014S mutation occurred at a very low frequency and was found only in Anopheles cruzi mosquitoes. The synergists PBO and EA partially restored susceptibility to pyrethroids and organochlorines, respectively, at all sites, while DEF increased susceptibility to carbamates and organophosphates at all sites except Anye. These data may help the Togolese National Malaria Control Program to develop more effective vector control strategies.
Post time: Dec-23-2024