PMI VectorLink project, Abidjan, Côte d'Ivoire.
Swiss Center of Scientific Research in Côte d'Ivoire, Abidjan, Côte d'Ivoire.
Malar J. 2020 Dec 9;19(1):454. doi: 10.1186/s12936-020-03523-y.
Pyrethroid-treated mosquito nets are currently the mainstay of vector control in Côte d'Ivoire. However, resistance to pyrethroids has been reported across the country, limiting options for insecticide resistance management due to the paucity of alternative insecticides. Two types of insecticide-treated nets (ITNs), ITNs with pyrethroids and the synergist piperonyl butoxide (PBO), and Interceptor®G2 nets, a net treated with a combination of chlorfenapyr and alpha-cypermethrin, are believed to help in the control of pyrethroid-resistant mosquitoes.
The susceptibility of Anopheles gambiae sensu lato (s.l.) to pyrethroid insecticides with and without pre-exposure to PBO as well as to chlorfenapyr was investigated in fifteen sites across the country. Susceptibility tests were conducted on 2- to 4-day old adult female An. gambiae s.l. reared from larval collections. The resistance status, intensity, and effects of PBO on mortality after exposure to different concentrations of deltamethrin, permethrin and alpha-cypermethrin were determined using WHO susceptibility test kits. In the absence of a WHO-recommended standard protocol for chlorfenapyr, two interim doses (100 and 200 µg/bottle) were used to test the susceptibility of mosquitoes using the CDC bottle assay method.
Pre-exposure to PBO did not result in full restoration of susceptibility to any of the three pyrethroids for the An. gambiae s.l. populations from any of the sites surveyed. However, PBO pre-exposure did increase mortality for all three pyrethroids, particularly deltamethrin (from 4.4 to 48.9%). Anopheles gambiae s.l. from only one site (Bettie) were susceptible to chlorfenapyr at the dose of 100 µg active ingredient (a.i.)/bottle. At the dose of 200 µg (a.i.)/bottle, susceptibility was only recorded in 10 of the 15 sites.
Low mosquito mortality was found for pyrethroids alone, and while PBO increased mortality, it did not restore full susceptibility. The vector was not fully susceptible to chlorfenapyr in one third of the sites tested. However, vector susceptibility to chlorfenapyr seems to be considerably higher than for pyrethroids alone or with PBO. These data should be used cautiously when making ITN procurement decisions, noting that bioassays are conducted in controlled conditions and may not fully represent field efficacy where the host-seeking behaviours, which include free-flying activity are known to enhance pro-insecticide chlorfenapyr intoxication to mosquitoes.
在科特迪瓦，经杀虫剂处理的蚊帐目前是病媒控制的主要手段。然而，由于缺乏替代杀虫剂，全国各地都报告了对拟除虫菊酯的抗药性，这限制了杀虫剂抗药性管理的选择。两种类型的经杀虫剂处理的蚊帐（ITN），一种是含有拟除虫菊酯和增效剂增效醚（PBO）的 ITN，另一种是Interceptor®G2 网，一种用氯氟氰菊酯和 alpha-氯氰菊酯处理的网，据信有助于控制对拟除虫菊酯有抗药性的蚊子。
在全国 15 个地点，调查了按蚊（Anopheles gambiae sensu lato，s.l.）对含有和不含有增效醚（PBO）预暴露的拟除虫菊酯杀虫剂以及氯氟氰菊酯的敏感性。在从幼虫收集物中饲养的 2-4 天大的成年雌性按蚊（An. gambiae s.l.）上进行了敏感性测试。使用世界卫生组织（WHO）敏感性测试试剂盒，确定了抗药性程度、强度以及 PBO 对不同浓度的溴氰菊酯、氯菊酯和 alpha-氯氰菊酯暴露后死亡率的影响。由于没有氯氟氰菊酯的世界卫生组织（WHO）推荐标准方案，因此使用 CDC 瓶测定法，使用两个临时剂量（100 和 200μg/瓶）来测试蚊子的敏感性。
在所有调查地点的种群中，增效醚预暴露都没有使三种拟除虫菊酯的敏感性完全恢复。然而，增效醚预暴露确实增加了所有三种拟除虫菊酯的死亡率，特别是溴氰菊酯（从 4.4 到 48.9%）。在一个地点（Bettie）的按蚊（An. gambiae s.l.）对 100μg 有效成分（a.i.）/瓶的氯氟氰菊酯敏感。在 200μg（a.i.）/瓶的剂量下，仅在 15 个地点中的 10 个地点记录到了敏感性。
单独使用拟除虫菊酯时，蚊子死亡率较低，而增效醚虽然增加了死亡率，但并没有完全恢复敏感性。在三分之一的测试地点，蚊子对氯氟氰菊酯没有完全敏感。然而，与单独使用拟除虫菊酯或增效醚相比，蚊子对氯氟氰菊酯的敏感性似乎要高得多。在做出 ITN 采购决策时，应谨慎使用这些数据，需要注意的是，生物测定是在受控条件下进行的，而在野外环境中，宿主寻找行为可能会增强蚊子对氯氟氰菊酯的中毒作用，而这种行为包括自由飞行活动。
