Microdistribution of the resistance of malaria vectors to deltamethrin in the region of Plateau (southeastern Benin) in preparation for an assessment of the impact of resistance on the effectiveness of Long Lasting Insecticidal Nets (LLINs)

Background: This study aims to research two areas, one with a resistant and the other with a susceptible profile of An. gambiae to deltamethrin in the region of Plateau (southern Benin). In each area, eight localities were sought. Both areas were needed for the assessment of the impact of malaria vector resistance to pyrethroids on the effectiveness of Long Lasting Insecticidal Nets (LLINs). The susceptible area of An. gambiae to deltamethrin was used as a control. Methods: In total, 119 localities in the region of Plateau were screened by sampling An. gambiae s.l larvae. Female mosquitoes resulting from these larvae were exposed to 0.05% deltamethrin following WHO standards. PCR was used to identify species and molecular forms of the dead and alive mosquitoes. Finally, we identified kdr mutations (1014 F and 1014S) using the HOLA technique. Results: Fifty-six out of 119 prospected localities tested positive for Anopheles gambae s.l breeding sites. The results showed that An. gambiae was resistant to deltamethrin in 39 localities and susceptible in only 2 localities; resistance to deltamethrin was suspected in 15 localities. The HOLA technique confirmed the presence of kdr 1014 F mutation and the absence of kdr 1014S mutation. The kdr 1014 F mutation was found in both M and S molecular forms at relatively high frequencies therefore confirming the susceptibility tests. Conclusion: We were unable to identify the eight susceptible areas due to the overall resistance of An. gambiae to deltamethrin in the region of Plateau. To implement the study, we kept two areas, one with high resistance (R+++) and the other with low resistance (R+) of An. gambiae to deltamethrin

Impact of long-lasting, insecticidal nets on anaemia and prevalence of Plasmodium falciparum among children under five years in areas with highly resistant malaria vectors

Background: The widespread use of insecticide-treated nets (LLINs) leads to the development of vector resistance to insecticide. This resistance can reduce the effectiveness of LLIN based interventions and perhaps reverse progress in reducing malaria morbidity. To prevent such difficulty, it is important to know the real impact of resistance in the effectiveness of mosquito nets. Therefore, an assessment of LLIN efficacy was conducted in malaria prevention among children in high and low resistance areas. Methods: The study was conducted in four rural districts and included 32 villages categorized as low or high resistance areas in Plateau Department, south-western Benin. Larvae collection was conducted to measure vector susceptibility to deltamethrin and knockdown resistance (kdr) frequency. In each resistance area, around 500 children were selected to measure the prevalence of malaria infection as well as the prevalence of anaemia associated with the use of LLINs. Results: Observed mortalities of Anopheles gambiae s. s population exposed to deltamethrin ranged from 19 to 96%. Knockdown resistance frequency was between 38 and 84%. The prevalence of malaria infection in children under five years was 22.4% (19.9-25.1). This prevalence was 17.3% (14.2-20.9) in areas of high resistance and 27.1% (23.5-31.1) in areas of low resistance (p = 0.04). Eight on ten children that were aged six - 30 months against seven on ten of those aged 31-59 months were anaemic. The anaemia observed in the six to 30-month old children was significantly higher than in the 31-59 month old children (p = 0.00) but no difference associated with resistance areas was observed (p = 0.35). The net use rate was 71%. The risk of having malaria was significantly reduced (p < 0.05) with LLIN use in both low and high resistance areas. The preventive effect of LLINs in high resistance areas was 60% (95% CI: 40-70), and was significantly higher than that observed in low resistance areas (p < 0.05). Conclusion: The results of this study showed that the resistance of malaria vectors seems to date not have affected the impact of LLINs and the use of LLINs was highly associated with reduced malaria prevalence irrespective of resistance