Azizi Salum, Snetselaar Janneke, Wright Alexandra, Matowo Johnson, Shirima Boniface, Kaaya Robert, Athumani Rashid, Tenu Filemoni, Protopopoff Natacha, Kirby Matthew
Department of Medical Parasitology and Entomology, Kilimanjaro Christian Medical University College, Moshi 255, Tanzania.
Pan African Malaria Vector Research Consortium, Moshi 255, Tanzania.
Insects. 2021 Aug 8;12(8):710. doi: 10.3390/insects12080710.
The emergence and spread of insecticide resistance in malaria vectors to major classes of insecticides call for urgent innovation and application of insecticides with novel modes of action. When evaluating new insecticides for public health, potential candidates need to be screened against both susceptible and resistant mosquitoes to determine efficacy and to identify potential cross-resistance to insecticides currently used for mosquito control. The challenges and lessons learned from establishing, maintaining, and authenticating the pyrethroid-resistant s.s. Muleba-Kis strain at the KCMUCo-PAMVERC Test Facility are described in this paper.
Male mosquitoes from the F generation of wild-pyrethroid resistant mosquitoes were cross-bred with susceptible female s.s. Kisumu laboratory strain followed by larval selection using a pyrethroid insecticide solution. Periodic screening for phenotypic and genotypic resistance was done. WHO susceptibility tests and bottle bioassays were used to assess the phenotypic resistance, while Taqman™ assays were used to screen for known target-site resistance alleles ( and ). Additionally, the strains were periodically assessed for quality control by monitoring adult weight and wing length.
By out-crossing the wild mosquitoes with an established lab strain, a successful resistant insectary colony was established. Intermittent selection pressure using alphacypermethrin has maintained high mutation (leucine-serine) frequencies in the selected colony. There was consistency in the wing length and weight measurements from the year 2016 to 2020, with the exception that one out of four years was significantly different. Mean annual wing length varied between 0.0142-0.0028 mm compared to values obtained in 2016, except in 2019 where it varied by 0.0901 mm. Weight only varied by approximately 0.001 g across four years, except in 2017 where it differed by 0.005 g. Routine phenotypic characterization on Muleba-Kis against pyrethroids using the WHO susceptibility test indicated high susceptibility when type I pyrethroids were used compared to type II pyrethroids. Dynamics on susceptibility status also depended on the lapse time when the selection was last done.
This study described the procedure for introducing, colonizing, and maintaining a resistant s.s. strain in the laboratory with leucine to serine substitution allele which reflects the features of the wild-resistant population in East Africa. Challenges in colonizing a wild-resistant mosquito strain were overcome by out-crossing between mosquito strains of desired traits followed by intermittent insecticide selection at the larval stage to select for the resistant phenotype.
疟疾病媒对主要类别的杀虫剂产生抗药性并传播，这就需要紧急创新并应用具有新作用方式的杀虫剂。在评估用于公共卫生的新型杀虫剂时，需要针对易感和抗性蚊子对潜在候选物进行筛选，以确定其效力，并确定对目前用于控制蚊子的杀虫剂是否存在潜在的交叉抗性。本文描述了在KCMUCo - PAMVERC测试设施建立、维持和鉴定拟除虫菊酯抗性斯氏按蚊穆勒巴 - 基斯菌株过程中所面临的挑战及吸取的经验教训。
将野生拟除虫菊酯抗性蚊子F代的雄蚊与易感的斯氏按蚊基苏木实验室品系的雌蚊杂交，然后使用拟除虫菊酯杀虫剂溶液进行幼虫选择。定期进行表型和基因型抗性筛选。采用世卫组织敏感性试验和瓶内生物测定法评估表型抗性，同时使用Taqman™测定法筛选已知的靶位点抗性等位基因（ 和 ）。此外，通过监测成虫体重和翅长对菌株进行定期质量控制评估。
通过将野生蚊子与已建立的实验室品系杂交，成功建立了一个抗性昆虫饲养群体。使用高效氯氰菊酯的间歇性选择压力使所选群体中 突变（亮氨酸 - 丝氨酸）频率保持在较高水平。2016年至2020年期间翅长和体重测量结果具有一致性，只有四年中的一年存在显著差异。与2016年获得的值相比，年平均翅长在0.0142 - 0.0028毫米之间变化，2019年除外，其变化为0.0901毫米。四年间体重仅相差约0.001克，2017年除外，其相差0.005克。使用世卫组织敏感性试验对穆勒巴 - 基斯进行的拟除虫菊酯常规表型特征分析表明，与II型拟除虫菊酯相比，使用I型拟除虫菊酯时敏感性较高。敏感性状态的动态变化还取决于上次进行选择后的时间间隔。
本研究描述了在实验室引入、定殖和维持具有亮氨酸到丝氨酸替代 等位基因的抗性斯氏按蚊品系的过程，该等位基因反映了东非野生抗性种群的特征。通过所需性状的蚊种间杂交，然后在幼虫阶段进行间歇性杀虫剂选择以选择抗性表型，克服了定殖野生抗性蚊种的挑战。
