Department of Disease Control, London School of Hygiene & Tropical Medicine, London, UK.
Department of Population Medicine, College of Medicine, Qatar University, Doha, Qatar.
Parasit Vectors. 2019 Mar 25;12(1):143. doi: 10.1186/s13071-019-3401-3.
The biting behaviour and dispersal of insect vectors in the field underlies the transmission of many diseases. Here, a novel collection methodology coupled with the molecular analysis of blood-meal sources and digestion rates is introduced with the aim of aiding the understanding of two critical and relatively understudied mosquito behaviours: plasticity in blood-host choice and vector dispersal.
A collection strategy utilising a transect of mosquito traps placed at 50 m intervals allowed the collection of blood-fed Anopheles coluzzii from a malaria-endemic village of southern Ghana where human host availability ranged from zero (a cattle pen), increasing until humans were the dominant host choice (the middle of the village). Blood-meal analysis using PCR showed statistically significant variation in blood-meal origins for mosquitoes collected across the 250 m transect: with decreasing trend in Bovine Blood Index (OR = 0.60 95% CI: 0.49-0.73, P < 0.01) and correspondingly, an increasing trend in Human Blood Index (OR = 1.50 95% CI: 1.05-2.16, P = 0.028) as the transect approached the village. Using qPCR, the host DNA remaining in the blood meal was quantified for field-caught mosquitoes and calibrated according to timed blood digestion in colony mosquitoes. Time since blood meal was consumed and the corresponding distance the vector was caught from its blood-host allowed the estimation of An. coluzzii dispersal rates. Within 7 hours of feeding, mosquitoes typically remained within 50 m of their blood-host but at 60 hours they had dispersed up to 250 m.
Using this methodology the remarkably small spatial scale at which An. coluzzii blood-host choice can change was demonstrated. In addition, conducting qPCR on host blood from field-caught mosquitoes and calibrating with timed experiments with colonised mosquitoes presents a novel methodology for investigating the dispersal behaviour of vectors. Future adaptations to this novel method to make it broadly applicable to other types of setting are also discussed.
昆虫媒介在野外的叮咬行为和扩散是许多疾病传播的基础。在这里，引入了一种新的采集方法，结合血液来源的分子分析和消化率，旨在帮助理解两种关键且相对研究不足的蚊子行为：血液宿主选择的可塑性和媒介扩散。
利用在 50 米间隔放置的蚊蝇诱捕器的收集策略，可以从加纳南部疟疾流行的一个村庄收集到吸食血液的疟蚊 Anopheles coluzzii，在那里人类宿主的可用性从零（牛栏）增加，直到人类成为主要的宿主选择（村庄的中间）。使用 PCR 进行的血液分析显示，在跨越 250 米的诱捕器收集的蚊子的血液来源方面存在统计学上显著的变化：牛血指数呈下降趋势（OR=0.60 95%CI：0.49-0.73，P<0.01），相应地，人血指数呈上升趋势（OR=1.50 95%CI：1.05-2.16，P=0.028），随着诱捕器接近村庄。使用 qPCR 对野外捕获的蚊子中的宿主 DNA 进行定量，并根据在实验室蚊子中的定时血液消化进行校准。根据蚊子消耗血液后的时间和它们从血液宿主处被捕获的距离，可以估计疟蚊 An. coluzzii 的扩散率。在进食后 7 小时内，蚊子通常仍在离其血液宿主 50 米以内，但在 60 小时后，它们已经扩散了 250 米。
使用这种方法，可以证明疟蚊 An. coluzzii 血液宿主选择的空间范围非常小。此外，对野外捕获的蚊子中的宿主血液进行 qPCR 分析，并通过与实验室蚊子的定时实验进行校准，为研究媒介的扩散行为提供了一种新的方法。还讨论了对这种新方法的未来改进，以使它广泛适用于其他类型的环境。
