Department of Parasitology, Faculty of Medicine, University of Colombo, Colombo, Sri Lanka.
Department of Zoology, Faculty of Science, University of Peradeniya, Peradeniya, Sri Lanka.
Parasit Vectors. 2020 May 13;13(1):246. doi: 10.1186/s13071-020-04117-y.
Leishmania donovani-induced and sand fly-transmitted leishmaniasis is a growing health problem in Sri Lanka. Limited knowledge on biological and behavioral characteristics of probable vector Phlebotomus argentipes hinders disease control. Here, insecticide susceptibility patterns of P. argentipes were investigated with exploration of probable underlying resistance mechanisms.
Adult sand flies were collected using standard cattle baited net traps and CDC light traps from selected sites in four districts. Adult F1 progeny of P. argentipes were exposed to different concentrations of DDT, malathion, deltamethrin and propoxur using WHO susceptibility bioassay kits. Post-1-h knockdown and post-24-h mortality were recorded and analyzed. Metabolic enzyme activity and the sensitivity of the acetylcholinesterase target-site were determined by biochemical assays using wild-caught flies. Extracted fly DNA samples were tested for the presence of knockdown-resistance (kdr) type mutations.
The LC values for DDT, malathion, propoxur and deltamethrin were 0.8-1.5%, 0.9-2.0%, 0.017-0.03% and 0.007% respectively. Insecticide-susceptibility levels were higher than the discriminating dosages established for Aedes mosquitoes, except for malathion. The lowest susceptibility levels (except for deltamethrin) were detected in the Mamadala population, whereas the highest levels were detected in the Mirigama population. The percentage of knocked-down sand flies was < 75% at any tested concentration, including those, which exhibited 100% mortality after 24 h. Elevated activity levels of glutathione S-transferase (3%, 7%, 12.5% and 14%) and esterase (2%, 5%, 5.5% and 6.5%) were detected in flies that originated from Mirigama, Pannala, Thalawa and Mamadala respectively, while monooxygenase quantities remained below the cut-off level. Ten to 34.5% of flies were heterozygous for acetylcholinesterases target-site insensitivity, associated with organophosphate and carbamate resistance. Pyrethroid-resistance-associated L1014F kdr-type mutation in the voltage gated sodium channel gene was detected in 30/53 flies.
Populations of P. argentipes in Sri Lanka are largely susceptible to common insecticides, except for malathion (used extensively in the past for malaria control). Their insecticide susceptibility appears negatively associated with past malaria endemicity of the study sites, with signs of early insecticide tolerance. Presence of insecticide target site insensitivity in a notable proportion of flies and enhanced insecticide metabolizing enzyme activities imply potential future challenges for leishmaniasis control, with a call for urgent proactive measures for its containment.
杜氏利什曼原虫引起的并通过沙蝇传播的利什曼病是斯里兰卡日益严重的健康问题。对可能的媒介白蛉 Phlebotomus argentipes 的生物学和行为特征的了解有限，这阻碍了疾病的控制。在这里，研究了 P. argentipes 的杀虫剂敏感性模式，并探索了可能的潜在抗性机制。
使用标准的牛诱饵网陷阱和疾病预防控制中心的诱虫灯从四个地区的选定地点收集成年沙蝇。使用世界卫生组织（WHO）敏感性生物测定试剂盒，对 P. argentipes 的成年 F1 后代暴露于不同浓度的滴滴涕、马拉硫磷、溴氰菊酯和残杀威。记录和分析 1 小时后击倒和 24 小时后死亡率。使用从野外捕获的苍蝇进行生化测定来确定代谢酶活性和乙酰胆碱酯酶靶标的敏感性。提取的蝇 DNA 样本用于检测击倒抗性（kdr）型突变。
滴滴涕、马拉硫磷、残杀威和溴氰菊酯的 LC 值分别为 0.8-1.5%、0.9-2.0%、0.017-0.03%和 0.007%。除马拉硫磷外，这些杀虫剂的敏感性水平均高于为伊蚊建立的区分剂量。在 Mamadala 种群中检测到最低的敏感性水平（除了溴氰菊酯），而在 Mirigama 种群中检测到最高的敏感性水平。在任何测试浓度下，击倒的沙蝇百分比均<75%，包括 24 小时后死亡率为 100%的沙蝇。来自 Mirigama、Pannala、Thalawa 和 Mamadala 的苍蝇的谷胱甘肽 S-转移酶（3%、7%、12.5%和 14%）和酯酶（2%、5%、5.5%和 6.5%）活性水平升高，而单氧化酶数量仍低于截止水平。10%至 34.5%的苍蝇为乙酰胆碱酯酶靶标不敏感的杂合子，与有机磷和氨基甲酸酯的抗性有关。在 53 只苍蝇中检测到电压门控钠离子通道基因中的 L1014F kdr 型突变与拟除虫菊酯抗性有关。
斯里兰卡的 P. argentipes 种群对常用杀虫剂的敏感性较高，除马拉硫磷（过去广泛用于疟疾控制）外。它们的杀虫剂敏感性似乎与研究地点过去疟疾的流行程度呈负相关，表明早期对杀虫剂的耐受性。相当比例的苍蝇对杀虫剂靶标的不敏感性和杀虫剂代谢酶活性的增强表明，未来对利什曼病控制可能会带来挑战，需要采取紧急主动措施加以控制。
