Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya.
School of Biological Sciences, University of Nairobi, Nairobi, Kenya.
PLoS One. 2021 Mar 1;16(3):e0240771. doi: 10.1371/journal.pone.0240771. eCollection 2021.
Long Lasting Insecticidal Nets (LLINs) and indoor residual spraying (IRS) represent powerful tools for controlling malaria vectors in sub-Saharan Africa. The success of these interventions relies on their capability to inhibit indoor feeding and resting of malaria mosquitoes. This study sought to understand the interaction of insecticide resistance with indoor and outdoor resting behavioral responses of malaria vectors from Western Kenya.
The status of insecticide resistance among indoor and outdoor resting anopheline mosquitoes was compared in Anopheles mosquitoes collected from Kisumu and Bungoma counties in Western Kenya. The level and intensity of resistance were measured using WHO-tube and CDC-bottle bioassays, respectively. The synergist piperonyl butoxide (PBO) was used to determine if metabolic activity (monooxygenase enzymes) explained the resistance observed. The mutations at the voltage-gated sodium channel (Vgsc) gene and Ace 1 gene were characterized using PCR methods. Microplate assays were used to measure levels of detoxification enzymes if present.
A total of 1094 samples were discriminated within Anopheles gambiae s.l. and 289 within An. funestus s.l. In Kisian (Kisumu county), the dominant species was Anopheles arabiensis 75.2% (391/520) while in Kimaeti (Bungoma county) collections the dominant sibling species was Anopheles gambiae s.s 96.5% (554/574). The An. funestus s.l samples analysed were all An. funestus s.s from both sites. Pyrethroid resistance of An.gambiae s.l F1 progeny was observed in all sites. Lower mortality was observed against deltamethrin for the progeny of indoor resting mosquitoes compared to outdoor resting mosquitoes (Mortality rate: 37% vs 51%, P = 0.044). The intensity assays showed moderate-intensity resistance to deltamethrin in the progeny of mosquitoes collected from indoors and outdoors in both study sites. In Kisian, the frequency of vgsc-L1014S and vgsc-L1014F mutation was 0.14 and 0.19 respectively in indoor resting malaria mosquitoes while those of the outdoor resting mosquitoes were 0.12 and 0.12 respectively. The ace 1 mutation was present in higher frequency in the F1 of mosquitoes resting indoors (0.23) compared to those of mosquitoes resting outdoors (0.12). In Kimaeti, the frequencies of vgsc-L1014S and vgsc-L1014F were 0.75 and 0.05 respectively for the F1 of mosquitoes collected indoors whereas those of outdoor resting ones were 0.67 and 0.03 respectively. The ace 1 G119S mutation was present in progeny of mosquitoes from Kimaeti resting indoors (0.05) whereas it was absent in those resting outdoors. Monooxygenase activity was elevated by 1.83 folds in Kisian and by 1.33 folds in Kimaeti for mosquitoes resting indoors than those resting outdoors respectively.
The study recorded high phenotypic, metabolic and genotypic insecticide resistance in indoor resting populations of malaria vectors compared to their outdoor resting counterparts. The indication of moderate resistance intensity for the indoor resting mosquitoes is alarming as it could have an operational impact on the efficacy of the existing pyrethroid based vector control tools. The use of synergist (PBO) in LLINs may be a better alternative for widespread use in these regions recording high insecticide resistance.
长效杀虫蚊帐（LLINs）和室内滞留喷洒（IRS）是撒哈拉以南非洲控制疟疾媒介的有力工具。这些干预措施的成功依赖于它们抑制室内疟蚊取食和栖息的能力。本研究旨在了解肯尼亚西部疟蚊的室内和室外栖息行为反应与杀虫剂抗性相互作用。
在肯尼亚西部基苏木县和邦戈马县收集的按蚊中比较了室内和室外栖息按蚊种群的杀虫剂抗性状况。使用世界卫生组织管和CDC瓶生物测定法分别测量了水平和强度的抗性。使用增效剂胡椒基丁醚（PBO）来确定代谢活性（单氧化酶酶）是否解释了观察到的抗性。使用聚合酶链反应（PCR）方法对电压门控钠通道（Vgsc）基因和 Ace 1 基因的突变进行了特征描述。如果存在解毒酶，则使用微孔板测定法来测量其水平。
在按蚊属中总共区分了 1094 个样本，在按蚊属中区分了 289 个样本。在基西安（基苏木县），优势种为阿拉伯按蚊 75.2%（391/520），而在基迈提（邦戈马县）采集的样本中，优势种为冈比亚按蚊 s.s 96.5%（554/574）。分析的按蚊属样本均为来自两个地点的按蚊属 s.s。在所有地点均观察到按蚊属 s.l 的拟除虫菊酯抗性。与室外栖息的蚊子相比，室内栖息的蚊子后代对溴氰菊酯的死亡率较低（死亡率：37%对 51%，P=0.044）。强度测定表明，在两个研究地点室内和室外收集的蚊子后代对溴氰菊酯均表现出中等强度的抗性。在基西安，室内栖息的疟蚊 vgsc-L1014S 和 vgsc-L1014F 突变的频率分别为 0.14 和 0.19，而室外栖息的蚊子的频率分别为 0.12 和 0.12。ace 1 突变在室内栖息的蚊子的 F1 中更为常见（0.23），而在室外栖息的蚊子中则较为罕见（0.12）。在基迈提，室内采集的蚊子 F1 中 vgsc-L1014S 和 vgsc-L1014F 的频率分别为 0.75 和 0.05，而室外栖息的蚊子的频率分别为 0.67 和 0.03。ace 1 G119S 突变存在于基迈提室内栖息蚊子的后代中（0.05），而在室外栖息的蚊子中则不存在。与室外栖息的蚊子相比，室内栖息的蚊子的单氧化酶活性分别高出 1.83 倍和 1.33 倍。
与室外栖息的蚊子相比，室内栖息的蚊子的表型、代谢和基因型杀虫剂抗性均较高。室内栖息蚊子的中等强度抗性表明，这可能对基于拟除虫菊酯的现有媒介控制工具的功效产生操作影响。在这些记录高杀虫剂抗性的地区，增效剂（PBO）在长效杀虫蚊帐中的使用可能是一种更好的替代选择。
