Abstract
Background: Insecticides resistance in Anopheles mosquitoes limits Long-Lasting Insecticidal Nets (LLIN) used for malaria control in Africa, especially Benin. This study aimed to evaluate the bio-efficacy of current LLINs in an area where An. funestuss.l. and An. gambiae have developed multi-resistance to insecticides, and to assess in experimental huts the performance of a mixed combination of pyrethroids and piperonyl butoxide (PBO) treated nets on these resistant mosquitoes. Methods: The study was conducted at Kpomè, Southern Benin. The bio-efficacy of LLINs against An. funestus and An. gambiae was assessed using the World Health Organization (WHO) cone and tunnel tests. A released/recapture experiment following WHO procedures was conducted to compare the efficacy of conventional LLINs treated with pyrethroids only and LLINs with combinations of pyrethroids and PBO. Prior to huts trials, we confirmed the level of insecticide and PBO residues in tested nets using high performance liquid chromatography (HPLC). Results: Conventional LLINs (Type 2 and Type 4) have the lowest effect against local multi-resistant An. funestus s.s. and An. coluzzii populations from Kpomè. Conversely, when LLINs containing mixtures of pyrethroids and PBO (Type 1 and Type 3) were introduced in trial huts, we recorded a greater effect against the two mosquito populations (P < 0.0001). Tunnel test with An. funestus s.s. revealed mortalities of over 80% with this new generation of LLINs (Type 1 and Type 3),while conventional LLINs produced 65.53 ± 8.33% mortalities for Type 2 and 71.25 ±7.92% mortalities for Type 4. Similarly, mortalities ranging from 77 to 87% were recorded with the local populations of An. coluzzii. Conclusion: This study suggests the reduced efficacy of conventional LLINs (Pyrethroids alone) currently distributed in Benin communities where Anopheles populations have developed multi-insecticide resistance. The new generation nets (pyrethroids+PBO) proved to be more effective on multi-resistant populations of mosquitoes.
Highlights
Malaria is responsible for about 438,000 deaths with an estimated 214 million disease cases annually[1]
Two types of long lasting nets treated with permethrin+piperonyl butoxide (PBO) and deltamethrin+ PBO are the new generation of Long-Lasting Insecticidal Nets (LLIN) for improved resistance management[25,26]
This finding showed the important involvement of P450s genes in observed pyrethroids resistance in this study and confirms the results of synergist bioassays test performed with these same resistant mosquitoes as almost all individuals were dead when they were exposed to PBO and immediately after to deltamethrin
Summary
Malaria is responsible for about 438,000 deaths with an estimated 214 million disease cases annually[1]. A study by Agossa et al.[9] in the northern part of Benin, showed that the efficacy of existing malaria vector control tools treated with pyrethroid have decreased in wild An. gambiae s.l. populations. Two types of long lasting nets treated with permethrin+PBO and deltamethrin+ PBO are the new generation of LLINs for improved resistance management[25,26] These new generation nets have shown their efficacy on some resistant populations of Anopheles in experimental hut trials[25,27]. Insecticides resistance in Anopheles mosquitoes limits Long-Lasting Insecticidal Nets (LLIN) used for malaria control in Africa, especially Benin. This study aimed to evaluate the bio-efficacy of current LLINs in an area where An. funestus s.l. and An. gambiae have developed multi-resistance to insecticides, and to assess in experimental huts the performance of a mixed combination of pyrethroids and piperonyl butoxide (PBO) treated nets on these resistant mosquitoes. Mortalities ranging from 77 to 87% were recorded with the local populations of
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