Centre de Recherche Entomologique de Cotonou, Cotonou, Benin.
Faculty of Science and Technology of the University of Abomey-Calavi, Godomey, Benin.
Parasit Vectors. 2021 Apr 14;14(1):202. doi: 10.1186/s13071-021-04699-1.
Insecticide resistance is threatening the effectiveness of efforts to control malaria vectors in Benin. This study explores the levels and mechanisms of insecticide resistance in An. gambiae s.l. to pyrethroids.
Larvae were collected from August 2017 to July 2018 in five communes in southern Benin (Adjohoun, Allada, Bohicon, Cotonou, and Porto-Novo) representing diverse ecological regions, and were reared in Benin's insectary. Two- to five-day-old female mosquitoes from each district were exposed to multiple doses of deltamethrin and permethrin (1×, 2×, 5×, and 10×) using the WHO insecticide resistance intensity bioassay. The effect of pre-exposure to the synergist, piperonyl butoxide (PBO), was also tested at different pyrethroid doses. Molecular allele frequencies of kdr (1014F) and ace-1R (119S) insecticide resistance mutations and levels of detoxification enzymes were determined for mosquitoes sampled from each study area.
An. gambiae s.l. were resistant to pyrethroid-only exposure up to 10× the diagnostic doses in all the study sites for both deltamethrin and permethrin. Mortality was significantly higher in An. gambiae s.l. pre-exposed to PBO followed by exposure to deltamethrin or permethrin compared to mosquitoes exposed to deltamethrin or permethrin only (p < 0.001). The difference in mortality between deltamethrin only and PBO plus deltamethrin was the smallest in Cotonou (16-64%) and the greatest in Bohicon (12-93%). The mortality difference between permethrin only and PBO plus permethrin was the smallest in Cotonou (44-75%) and the greatest in Bohicon (22-72%). In all the study sites, the kdr resistance allele (1014F) frequency was high (75-100%), while the ace-1 resistance allele (G119S) frequency was low (0-3%). Analysis of the metabolic enzymatic activity of An. gambiae s.l. showed overexpression of nonspecific esterases and glutathione S-transferases (GST) in all study sites. In contrast to the PBO results, oxidase expression was low and was similar to the susceptible An. gambiae s.s. Kisumu strain in all sites.
There is high-intensity resistance to pyrethroids in southern Benin. However, pre-exposure to PBO significantly increased susceptibility to the pyrethroids in the different An. gambiae s.l. populations sampled. The use of PBO insecticide-treated bed nets may help maintain the gains in An. gambiae (s.l.) control in southern Benin.
杀虫剂耐药性正在威胁贝宁控制疟疾媒介的努力成效。本研究旨在探究冈比亚按蚊（An. gambiae s.l.）对拟除虫菊酯类杀虫剂的耐药水平和机制。
2017 年 8 月至 2018 年 7 月，我们在贝宁南部五个社区（阿乔洪、阿洛达、博希孔、科托努和波多诺伏）采集幼虫，这些社区代表了不同的生态区，并在贝宁的昆虫饲养室中进行饲养。每个地区的 2 至 5 日龄雌性蚊子分别暴露于不同剂量的溴氰菊酯和氯菊酯（1×、2×、5×和 10×），采用世界卫生组织杀虫剂抗药性强度生物测定法进行测试。我们还在不同的拟除虫菊酯剂量下测试了增效剂增效醚（PBO）的预暴露效果。对从每个研究区域采集的蚊子进行 kdr（1014F）和 ace-1R（119S）杀虫剂耐药突变的分子等位基因频率和解毒酶水平的测定。
在所有研究地点，冈比亚按蚊对拟除虫菊酯类杀虫剂的暴露水平高达诊断剂量的 10 倍，对溴氰菊酯和氯菊酯均表现出抗药性。与仅接触溴氰菊酯或氯菊酯的蚊子相比，预先接触 PBO 然后再接触溴氰菊酯或氯菊酯的冈比亚按蚊死亡率显著更高（p<0.001）。在科托努，仅接触溴氰菊酯和接触 PBO 加溴氰菊酯之间的死亡率差异最小（16-64%），而在博希孔，死亡率差异最大（12-93%）。仅接触氯菊酯和接触 PBO 加氯菊酯之间的死亡率差异在科托努最小（44-75%），在博希孔最大（22-72%）。在所有研究地点，kdr 耐药等位基因（1014F）的频率均很高（75-100%），而 ace-1 耐药等位基因（G119S）的频率较低（0-3%）。对冈比亚按蚊 s.l.代谢酶活性的分析表明，在所有研究地点，非特异性酯酶和谷胱甘肽 S-转移酶（GST）的过度表达。与 PBO 结果相反，氧化酶的表达较低，与所有地点的敏感品系冈比亚按蚊 Kisumu 相似。
在贝宁南部，对拟除虫菊酯类杀虫剂的耐药性很高。然而，预先接触 PBO 可显著提高不同冈比亚按蚊 s.l.种群对拟除虫菊酯类杀虫剂的敏感性。使用 PBO 处理过的驱虫蚊帐可能有助于维持在贝宁南部控制冈比亚按蚊（s.l.）的成果。
