Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, SY23 3FG, UK.
Lincoln Centre for Water and Planetary Health, School of Geography, College of Science, Think Tank, University of Lincoln, Ruston Way, Lincoln, LN6 7DW, UK.
Parasit Vectors. 2021 Feb 1;14(1):91. doi: 10.1186/s13071-020-04540-1.
The Barotse floodplains of the upper Zambezi River and its tributaries are a highly dynamic environment, with seasonal flooding and transhumance presenting a shifting mosaic of potential larval habitat and human and livestock blood meals for malaria vector mosquitoes. However, limited entomological surveillance has been undertaken to characterize the vector community in these floodplains and their environs. Such information is necessary as, despite substantial deployment of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) against Anopheles vectors, malaria transmission persists across Barotseland in Zambia's Western Province.
Geographically extensive larval surveys were undertaken in two health districts along 102 km of transects, at fine spatial resolution, during a dry season and following the peak of the successive wet season. Larvae were sampled within typical Anopheles flight range of human settlements and identified through genetic sequencing of cytochrome c oxidase I and internal transcribed spacer two regions of mitochondrial and nuclear DNA. This facilitated detailed comparison of taxon-specific abundance patterns between ecological zones differentiated by hydrological controls.
An unexpected paucity of primary vectors was revealed, with An. gambiae s.l. and An. funestus representing < 2% of 995 sequenced anophelines. Potential secondary vectors predominated in the vector community, primarily An. coustani group species and An. squamosus. While the distribution of An. gambiae s.l. in the study area was highly clustered, secondary vector species were ubiquitous across the landscape in both dry and wet seasons, with some taxon-specific relationships between abundance and ecological zones by season.
The diversity of candidate vector species and their high relative abundance observed across diverse hydro-ecosystems indicate a highly adaptable transmission system, resilient to environmental variation and, potentially, interventions that target only part of the vector community. Larval survey results imply that residual transmission of malaria in Barotseland is being mediated predominantly by secondary vector species, whose known tendencies for crepuscular and outdoor biting renders them largely insensitive to prevalent vector control methods.
赞比西河上游及其支流的巴罗策泛滥平原是一个高度动态的环境，季节性洪水泛滥和牲畜迁徙使得潜在的幼虫栖息地以及人类和牲畜的疟疾病媒蚊血餐呈现出不断变化的镶嵌模式。然而，对这些泛滥平原及其周围地区的媒介群落进行特征描述的昆虫学监测十分有限。尽管在赞比亚西部省的巴罗策兰大规模部署了经杀虫剂处理的蚊帐（ITN）和室内滞留喷洒（IRS），但疟疾仍在持续传播。
在旱季和随后的湿季高峰期，沿着 102 公里的横断面，在 102 公里的横截线上进行了广泛的幼虫调查，以精细的空间分辨率进行。在人类住区典型的疟疾病媒蚊飞行范围内采集幼虫，并通过对细胞色素 c 氧化酶 I 和线粒体和核 DNA 的内部转录间隔区 2 区域的基因测序来识别。这有助于在通过水文控制区分的生态区之间详细比较分类群特异性丰度模式。
出乎意料的是，主要媒介的数量非常少，冈比亚按蚊复合体和冈比亚疟蚊只占 995 条测序按蚊的<2%。潜在的次要媒介在媒介群落中占主导地位，主要是库斯塔尼组物种和斯夸莫休斯按蚊。虽然研究区域内冈比亚按蚊复合体的分布高度聚集，但次要媒介物种在旱季和湿季都在整个景观中无处不在，有些特定分类群与生态区之间存在季节性关系。
在不同的水-生态系统中观察到候选媒介物种的多样性及其相对较高的丰度表明，传播系统具有高度的适应性，能够抵御环境变化，并且可能对仅针对部分媒介群落的干预措施具有抵抗力。幼虫调查结果表明，巴罗策兰的疟疾残留传播主要由次要媒介物种介导，这些媒介物种黄昏和户外叮咬的倾向使得它们对普遍存在的媒介控制方法基本上不敏感。
