BACKGROUND The Sahel region of Chad Republic is a prime candidate for malaria pre-elimination. To facilitate pre-elimination efforts in this region, two populations of Anopheles coluzzii from Central Chad Republic were characterized, their insecticide resistance profile and the possible molecular mechanisms driving the resistance in the field investigated. METHODS Bloodfed female Anopheles gambiae s.l. resting indoor, were collected at N'djamena and Massakory, Chad in 2018 and characterized for species composition, and infection rate was determined using the TaqMan assay. Susceptibility to various insecticides was assessed using WHO tube bioassays. Cone bioassays were conducted using various long-lasting insecticidal nets (LLINs). Results were analysed using Chi Square test. Knockdown resistance (kdr) and ace-1 markers were investigated by TaqMan genotyping. RESULTS Anopheles coluzzii was the major vector found in N'djamena (100%) and Massakory (~ 94%). No Plasmodium was found in 147 bloodfed F0 An. coluzzii (82 from N'djamena and 65 from Massakory). High intensity pyrethroid resistance was observed with mortalities of < 2% for permethrin, deltamethrin and etofenprox, and with < 50% and < 60% dead following exposure to 10× diagnostic doses of deltamethrin and permethrin, respectively. For both sites, < 10% mortalities were observed with DDT. Synergist bioassays with piperonylbutoxide significantly recovered pyrethroid susceptibility in Massakory populations, implicating CYP450s (mortality = 13.6% for permethrin, χ2 = 22.8, df = 1, P = 0.0006; mortality = 13.0% for deltamethrin, χ2 = 8.8, df = 1, P < 0.00031). Cone-bioassays established complete loss of efficacy of the pyrethroid-based LLINs; and a 100% recovery of susceptibility following exposure to the roof of PermaNet®3.0, containing piperonylbutoxide. Both populations were susceptible to malathion, but high bendiocarb resistance was observed in Massakory population. The absence of ace-1 mutation points to the role of metabolic resistance in the bendiocarb resistance. Both 1014F and 1014S mutations were found in both populations at around 60% and < 20% respectively. Sequencing of intron-1 of the voltage-gated sodium channel revealed a low genetic diversity suggesting reduced polymorphism. CONCLUSIONS Multiple resistance in An. coluzzii populations from Chad highlight challenges associated with deployment of LLINs and indoor residual spraying (IRS) in the Sahel of this country. The pyrethroid-synergists LLINs (e.g. PermaNet®3.0) and organophosphate-based IRS maybe the alternatives for malaria control in this region.

中文翻译：

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乍得共和国主要疟疾病媒Anopheles coluzzii对杀虫剂具有高抗药性。


背景 乍得共和国萨赫勒地区是疟疾预消灭的主要候选地区。为了促进该地区的预消灭工作，对来自乍得共和国中部的两个按蚊种群进行了表征，研究了它们的杀虫剂抗性概况以及在实地调查中驱动抗性的可能分子机制。方法 2018 年在乍得恩贾梅纳和马萨科里收集在室内休息的吸血雌性冈比亚按蚊，并对其物种组成进行表征，并使用 TaqMan 测定法确定感染率。使用世界卫生组织试管生物测定法评估对各种杀虫剂的敏感性。使用各种长效杀虫网（LLIN）进行锥孔生物测定。使用卡方检验分析结果。通过 TaqMan 基因分型研究敲低抗性 (kdr) 和 ace-1 标记。结果 葛氏按蚊是在恩贾梅纳 (100%) 和马萨科里 (~ 94%) 发现的主要媒介。 147 只血饲 F0 An 中未发现疟原虫。 coluzzii（82 例来自恩贾梅纳，65 例来自马萨科里）。观察到高强度拟除虫菊酯抗性，氯菊酯、溴氰菊酯和依托芬菊死亡率为 < 2%，暴露于 10 倍诊断剂量的溴菊酯和氯菊酯后死亡率分别为 < 50% 和 < 60%。对于这两个地点，使用 DDT 观察到 < 10% 死亡率。使用胡椒基丁醚进行的增效剂生物测定显着恢复了 Massakory 群体中拟除虫菊酯的敏感性，涉及 CYP450（氯菊酯死亡率 = 13.6%，χ2 = 22.8，df = 1，P = 0.0006；溴氰菊酯死亡率 = 13.0%，χ2 = 8.8，df = 1，P < 0.00031)。 锥体生物测定证实基于拟除虫菊酯的 LLIN 完全丧失功效；暴露于含有胡椒基丁醚的 PermaNet®3.0 屋顶后，敏感性 100% 恢复。两个种群均对马拉硫磷敏感，但在 Massakory 种群中观察到对苯硫威具有较高的耐药性。 ace-1 突变的缺失表明代谢抗性在苯虫威抗性中发挥了作用。在两个群体中均发现 1014F 和 1014S 突变，分别约为 60% 和 < 20%。电压门控钠通道内含子 1 的测序显示遗传多样性较低，表明多态性减少。结论 An 中存在多重耐药性。来自乍得的 coluzzii 种群凸显了在该国萨赫勒地区部署 LLIN 和室内滞留喷洒 (IRS) 所面临的挑战。拟除虫菊酯增效剂LLIN（例如PermaNet®3.0）和基于有机磷的IRS可能是该地区控制疟疾的替代方案。