Identifying molecular determinants of drug susceptibility in salmon lice (Lepeophtheirus salmonis)

鲑鱼虱是一种甲壳类体外寄生虫，感染野生和养殖的鲑鱼，给大西洋鲑鱼养殖业带来了严重的问题。养殖场的鲑鱼虱子感染需要控制，以维持良好的鱼类健康和福利，并将养殖场来源的寄生虫对野生鱼类种群的潜在影响降至最低。目前，养鱼场的鲑鱼虱子控制在很大程度上依赖于药物的使用，并辅之以养殖场管理措施。目前正在制定一些非化学控制战略，其中包括通过清洁鱼类对虱子进行生物控制，以及试图通过接种疫苗和选择性繁殖方案使三文鱼对虱子具有抵抗力。然而，这些和其他替代控制策略目前还不足以在工业规模上全面实施。虽然抗寄生虫药物能够有效地控制鲑鱼虱子，但可用的除虫剂种类相对较少。从其他害虫和寄生虫中得知，在查尔斯·达尔文发现的自然选择机制的驱动下，重复使用相同或类似的化学物质会增加寄生虫产生抗药性的风险。某些被称为“抗性等位基因”的遗传特征在生物体中通常是罕见的，因为它们在正常情况下不会给携带者带来任何好处。然而，具有抗药性等位基因的寄生虫比没有抗药性等位基因的寄生虫能够更好地在药物治疗中存活，因此如果过度使用相同的药物，抗药性等位基因会增加它们在接受治疗的寄生虫种群中的频率，因为易感个体会被治疗杀死。这可能最终导致整个种群的抗药性。人们对鲑鱼虱子抗药性的机制知之甚少。在拟议的项目中，将使用实验室产生的具有抗药性的鲑鱼虱子菌株来研究潜在的抗药性机制。将遵循两种策略来找出这些虱子是如何产生抗药性的。首先，将在抗药性和对药物敏感的鲑鱼虱子之间进行杂交，并将使用最新的DNA测序方法识别与抗药性相关的基因序列。其次，将确定耐药和对药物敏感的鲑鱼虱子之间的基因表达差异，这将为特定分子途径参与特定药物耐药性的形成提供新的见解。这些知识将对识别可以打破耐药性机制的药物非常有用。目前，三文鱼养殖场可供选择的治疗方案是基于“生物检测”的结果，这是一种用于确定对治疗敏感性的小规模实验室治疗三文鱼虱子的方法。然而，鲑鱼虱子生物检测容易出错，而且经常无法正确预测后续养殖场治疗的成功。本项目将开发快速测试，以检测对治疗的遗传敏感性，在确定特定农场情况的最佳治疗选择方面，预计这些测试将比生物检测更具体和准确。利用现有最好的治疗方法具有明显的经济效益和环境效益，并有助于防止耐药性的发展。新的、未开发的毒品类别代表着对未来粮食安全具有高价值的有限自然资源。通过帮助对抗抗药性的发展，该项目将有助于延长现有和新型除虫剂的寿命，从而提高三文鱼集约化养殖的可持续性。

The salmon louse, Lepeophtheirus salmonis, is a crustacean ectoparasite infecting wild and farmed salmonid fishes, which causes significant problems in marine Atlantic salmon aquaculture. Salmon louse infections on farms require control to maintain good fish health and welfare, and to minimise potential impacts of farm-origin parasites on wild fish populations. Currently, salmon louse control on fish farms depends heavily upon the use of drugs, supplemented by farm management measures. A number of non-chemical control strategies are currently under development, and these include the biological control of lice through cleaner fish and attempts to render salmon resistant to lice through vaccination and selective breeding programmes. However, these and other alternative control strategies are presently not sufficiently developed to allow full implementation at an industrial scale.While anti-parasitic drugs offer efficient salmon louse control, relatively few types of delousing agents are available. It is known from other pests and parasites that the repeated use of the same or similar chemicals increases the risk that parasites may develop drug resistances, driven by the mechanisms of natural selection discovered by Charles Darwin. Certain genetic features, called "resistance alleles", are usually rare in organisms as they provide no benefits to their carriers under normal conditions. Parasites possessing resistance alleles, however, are able to survive drug treatments better than those without, hence if the same drug is over-used, resistance alleles can increase their frequency in treated parasite populations as susceptible individuals are killed by treatment. This may ultimately result in drug resistance of the entire population.Very little is known about the mechanisms responsible for drug resistance in salmon lice. In the proposed project, drug-resistant strains of salmon lice generated in the laboratory will be used to investigate potential resistance mechanisms. Two strategies will be followed to find out how these lice have managed to become drug resistant. Firstly, breeding crosses will be made between resistant and drug-susceptible salmon lice, and genetic sequences that are associated with resistance will be identified using the latest DNA sequencing methodologies. Secondly, differences in gene expression between resistant and drug-susceptible salmon lice will be determined, which will provide new insights into the involvement of particular molecular pathways in development of resistance to particular drugs. Such knowledge will be extremely useful in the identification of drugs which can break the resistance mechanism.Choices among available treatment options on salmon farms are currently based on the results of "bioassays", which are small-scale laboratory treatments of salmon lice used to establish susceptibility to treatment. However, salmon louse bioassays are error-prone and regularly fail to correctly predict the success of subsequent farm treatments. The present project will develop fast tests to detect genetic susceptibility to treatment that are expected to be more specific and accurate than bioassays in identifying the best treatment choice for a given farm situation. Using the best available treatment has obvious economic and environmental benefits, and can help to prevent resistance development. New, unexploited drug classes represent a limited natural resource of high value for future food security. By helping to combat the development of drug resistance, this project will help to extend the life of current and novel delousing agents, and thus improve the sustainability of intensive salmon farming.