Nematode parasitism of arbovirus vectors: effect of mermithids on Culicoides biting midges and their potential use for disease and vector control

咬蚊是一种微小的飞行昆虫，其中包括一种臭名昭著的物种，它困扰着苏格兰的部分地区。它们是最丰富的吸血昆虫之一，分布在大多数有人居住的世界。在欧洲，农场中常见的某些物种是家畜病毒的重要携带者。迄今为止，控制这些昆虫的方法尚未成功。2007年和2011年在英国出现的家畜疾病蓝舌病（BT）和施马伦贝格病（SB）突出表明，蚊媒传播的病毒是对英国的潜在威胁。它们还传播了非洲马病（AHS），这是一种高度致命的马病，被认为对欧洲构成威胁。迄今为止，已从蠓中分离出50多种病毒，通过临床疾病和动物贸易限制对经济产生了重大影响。BT正在欧洲大陆爆发，因此英国可能会进一步爆发。目前，我们依靠给动物接种疫苗来预防其中一些疾病，因为控制传播这些疾病的昆虫一直不成功。这种疫苗接种在英国家畜中并不经常进行，而且往往只有在疫情得到确认后才会进行。在欧洲，许多疾病（包括AHS和许多类型的BT）都没有获得许可使用的疫苗。因此，确定其他方法来管理此类疫情，以便在疫情爆发之前或发生疫情时采取知情的缓解程序是至关重要的。我的目的是调查一种高度流行的寄生虫（mermithid nematodes）对蠓的生物学影响，并确定它们是否影响蠓感染和传播牲畜病毒的能力。蠓是一种主要的线虫，生活在蠓和其他昆虫的幼虫体内，经常在它们出现时杀死它们；但可能会被携带到成虫体内，导致它们绝育。英国的蠓中存在这些狭缝虫，并且成功地使用狭缝虫控制蚊子种群表明它们可能具有控制蠓的潜力，但在欧洲没有关于这些蠓媒介寄生狭缝虫的信息。在利物浦大学，我使用来自英格兰和威尔士各地的库蠓，目的是研究这些线虫的分布，并评估这种分布在不同年份之间是否会发生变化。尽管它们很重要，但成功鉴定的蠓很少，因此我将使用基于dna的技术来确定寄生在英国蠓上的物种，然后建立可靠的鉴定技术，使其他研究人员能够在未来开展此类工作。任何可能对库蠓控制有用的寄生虫都必须有经济的大规模饲养方法，因此将建立实验室饲养方法，并确定储存和运输的可能性，以便以后进行现场试验。类似的饲养方法在美国已经取得了成功，该项目的这一部分将与加州大学河滨分校合作进行。最重要的是，将评估蠓寄生对蠓在感染BT和SB病毒之前的生命周期、繁殖和适应性的影响，并评估它们传播病毒的能力、实现感染所需的病毒剂量以及它们的存活。在这里，由皮尔布赖特研究所提供的野生捕获和群体饲养的蠓将在利物浦热带医学院感染mermithids和病毒。该项目将收集与广泛的节肢动物媒介有关的信息，例如英国蚊子，以及其他人类和牲畜媒介传播的疾病。如果发生疫情，这项工作可为更有效地控制病媒提供信息，并将为决策者提供有助于以下方面的信息：1)了解控制媒介传播疾病的方法；Ii)减少爆发的机会；Iii)更有效地应对爆发事件。

Biting midges are a group of tiny flying insects that include a notorious species that plagues parts of Scotland. They are one of the most abundant blood-feeding insects and occur throughout most of the inhabited world. Certain species commonly found on farms are important carriers of livestock viruses in Europe. Methods to control these insects have so far been unsuccessful.The emergence of the livestock diseases bluetongue (BT) in 2007 and Schmallenberg (SB) in 2011 in the UK highlight that midge transmitted viruses are a potential threat to the UK. They also spread African horse sickness (AHS), a highly lethal disease of horses, considered a risk to Europe. To date, over 50 viruses have been isolated from midges, causing significant economic impact through clinical disease and animal trade restrictions. Outbreaks of BT are ongoing in mainland Europe, so further outbreaks may occur in the UK. Currently we rely on vaccinating animals against some of these diseases, as control of insects transmitting them has been unsuccessful. Such vaccination is not routinely undertaken in UK livestock, and tends to only occur once an outbreak has been confirmed. Vaccines licensed for use in Europe do not exist for many diseases, including AHS and many types of BT. It is therefore paramount to determine other ways to manage such outbreaks to allow informed mitigation procedures in advance of, or in the event of, an outbreak.My aim is to investigate the effects of a highly prevalent parasitic worm (mermithid nematodes) on the biology of Culicoides midges and to determine whether they affect a midge's ability to be infected by and transmit livestock viruses. Mermithids are a major group of nematode that live inside the larvae of midges, and other insects, often killing them when they emerge; but may be carried into the adult insect, sterilizing them as a result. These mermithids are present in UK midges and the successful use of mermithids to control mosquito populations suggests that there may be potential in their use for midge control, yet no information exists on mermithid parasitism of these midge vectors in Europe.At the University of Liverpool, using Culicoides from across England and Wales, I aim to study the distribution of these nematodes and assess whether this changes between years. Despite their importance, very few mermithids have been successfully identified so I will use DNA-based techniques to determine the species parasitising UK midges, before establishing reliable identification techniques to enable other researchers to build on such work in the future. Any parasite which may be useful for Culicoides control must have an economical method of mass rearing, so a laboratory rearing method will be established and the possibility of storage and transportation determined, allowing field testing at a later date. Similar rearing methods have been successful in the USA, and this part of the project will be undertaken in collaboration with the University of California, Riverside. Most crucially, the effect of parasitism by mermithids will be assessed on the lifecycle, reproduction and fitness of the midges before being infected with BT and SB viruses and assessed for their ability to transmit virus, the dosage of virus needed to achieve infection, and their survival. Here both wild-caught and colony reared midges, supplied by the Pirbright Institute, will be infected with mermithids and virus at the Liverpool School of Tropical Medicine.This project will gather information relevant to a wide range of arthropod vectors, such as UK mosquitoes, as well as other humans and livestock vector-borne diseases. In the event of an outbreak the work may provide information for more effective vector control and will arm policy makers with information that can be useful for i) understanding methods to control midge-borne diseases; ii) reducing the chances of an outbreak occurring; iii) more effectively dealing with an outbreak occurrence.