Spatial and temporal development of deltamethrin resistance in malaria vectors of the Anopheles gambiae complex from North Cameroon

The effectiveness of insecticide-based malaria vector control interventions in Africa is threatened by the spread and intensification of pyrethroid resistance in targeted mosquito populations. The present study aimed at investigating the temporal and spatial dynamics of deltamethrin resistance in An. gambiae s.l. populations from North Cameroon. Mosquito larvae were collected from 24 settings of the Garoua, Pitoa and Mayo Oulo Health Districts (HDs) from 2011 to 2015. Two to five days old female An. gambiae s.l. emerging from larval collections were tested for deltamethrin resistance using the World Health Organization’s (WHO) standard protocol. Sub samples of test mosquitoes were identified to species using PCR-RFLP and genotyped for knockdown resistance alleles (Kdr 1014F and 1014S) using Hot Ligation Oligonucleotide Assay (HOLA). All the tested mosquitoes were identified as belonging to the An. gambiae complex, including 3 sibling species mostly represented by Anopheles arabiensis (67.6%), followed by Anopheles coluzzii (25.4%) and Anopheles gambiae (7%). Deltamethrin resistance frequencies increased significantly between 2011 and 2015, with mosquito mortality rates declining from 70–85% to 49–73% in the three HDs (Jonckheere-Terstra test statistic (JT) = 5638, PAn. gambiae s.l. populations over the 24 field populations monitored during the study period, from 2011 to 2015. Phenotypic resistance was mostly found in urban settings compared with semi-urban and rural settings (JT = 5282, PKdr 1014F allelic frequencies in study HDs increased from 0–30% in 2011 to 18–61% in 2014–2015 (JT = 620, P An. coluzzii samples. The overall frequency of the Kdr 1014S allele was 0.1%. This study revealed a rapid increase and widespread deltamethrin resistance frequency as well as Kdr 1014F allelic frequencies in An. gambiae s.l. populations over time, emphasizing the urgent need for vector surveillance and insecticide resistance management strategies in Cameroon.非洲基于杀虫剂的疟疾媒介控制干预措施的有效性，正受到靶标蚊虫种群中拟除虫菊酯抗性的传播与增强的威胁。本研究旨在调查喀麦隆北部冈比亚按蚊复合组（An. gambiae s.l.）种群中溴氰菊酯抗性的时空动态。2011至2015年间，研究人员从加鲁阿、皮托阿和马约乌洛卫生区（HDs）的24个采样点采集蚊虫幼虫。利用采集幼虫羽化得到的2至5日龄雌性冈比亚按蚊复合组个体，按照世界卫生组织（WHO）标准规程开展溴氰菊酯抗性检测。采用聚合酶链反应-限制性片段长度多态性（PCR-RFLP）对部分受试蚊虫进行物种鉴定，并通过热连接寡核苷酸检测（HOLA）对击倒抗性等位基因（Kdr 1014F和1014S）进行基因分型。所有受试蚊虫均属于冈比亚按蚊复合组，包含3个姊妹种，其中以阿拉伯按蚊（Anopheles arabiensis，占比67.6%）占比最高，其次为科鲁兹按蚊（Anopheles coluzzii，25.4%）和冈比亚按蚊（Anopheles gambiae，7%）。2011至2015年间，溴氰菊酯抗性频率显著上升，三个卫生区的蚊虫死亡率从70%~85%降至49%~73%（琼克赫雷-特斯特趋势检验统计量（JT）=5638，P<0.001）。与半城镇和农村采样点相比，表型抗性主要出现在城镇区域（JT=5282，P<0.001）。Kdr 1014F等位基因频率在研究涉及的卫生区从2011年的0~30%升至2014-2015年的18%~61%（JT=620，P<0.001），且在科鲁兹按蚊样本中尤为显著。Kdr 1014S等位基因的总体频率为0.1%。本研究揭示，随着时间推移，冈比亚按蚊复合种种群的溴氰菊酯抗性频率以及Kdr 1014F等位基因频率均快速上升且分布广泛，凸显了喀麦隆亟需开展媒介监测与杀虫剂抗性管理策略的紧迫性。