Insecticide resistance in Malaria vectors: Implications for control strategies in northern health districts of Cote d’Ivoire

Abstract

<title>Abstract</title> <bold>Background:</bold> Long-lasting insecticidal nets (LLINs) are the primary method used by the National Malaria Control Program (NMCP) to combat malaria. However, malaria vector resistance poses a serious threat to the success of vector control measures. The objective of this study was to analyze the current state of malaria vector resistance to commonly used insecticides in northern sentinel sites of Cote d’Ivoire. <bold>Methods:</bold> <italic>Anopheles</italic> larvae were sampled in Bouna, Korhogo, and Odienné. Adult females aged 2-5 days were subjected to various susceptibility tests according to the protocol recommended by the World Health Organization (WHO). Metabolic resistance was demonstrated by pre-exposure of mosquitoes to Piperonyl butoxide (PBO). Other insecticides such as Chlorfenapyr and Clothianidin were tested in anticipation of Indoor Residual Spraying (IRS) as a complementary vector control method in these areas. <italic>Anopheles gambiae s.l.</italic> complex subspecies were identified by polymerase chain reaction (PCR). <bold>Results:</bold> Resistance to pyrethroids, the fundamental chemical for treating LLINs, was strongly confirmed in the sentinel sites. Synergist tests demonstrated an increase in the mortality rate and restored susceptibility of malaria vectors after pre-exposure to Piperonyl butoxide (PBO). Identification of resistance mechanisms showed the presence of kdr-West and Ace-1 genes. Among these genes, kdr-West was found to be the most prevalent in the Anopheles gambiae population of Bouna (96%), Korhogo (98%), and Odienne (100%). Mosquitoes exhibited sensitivity to chlorfenapyr at a dose of 100 µg/bottle and 200 µg/bottle. However, mosquitoes showed resistance to clothianidin in each site, except for Odienné, where vectors were susceptible to this insecticide. <bold>Conclusions:</bold> The resistance of malaria vectors to commonly used insecticides is strongly confirmed in the savanna zone of northern Côte d'Ivoire. Resistance markers in this region are heterogeneous and the intensity of resistance could vary according to the ecological context of the sites. Chlorfenapyr emerges as a promising option for IRS programs, given its efficacy and absence of resistance observed in this study. Surveillance of insecticide resistance need to be continued to guide the selection of appropriate control measures.