Tully O, Nolan D T
Department of Zoology, Trinity College Dublin, Dublin, Ireland.
Parasitology. 2002;124 Suppl:S165-82. doi: 10.1017/s0031182002001889.
Lepeophtheirus salmonis is a specific parasite of salmonids that occurs in the Atlantic and Pacific Oceans. When infestations are heavy fish mortality can occur although the factors that are responsible for causing epizootics, especially in wild salmonid populations are still largely unknown. Over the past 20 years this parasite has caused significant economic losses in farmed salmon production and possibly in wild salmonid populations locally. Understanding the connectivity between populations is crucial to an understanding of the epidemiology of infections and for management of infections in aquaculture. Data from genetics, pesticide resistance, larval dispersal models and spatial and temporal patterns of infestation in wild and farmed hosts suggests a spatially highly structured metapopulation the components of which have different levels of connectivity, probabilities of extinction and influence on the development of local infestations. The population structure is defined mainly by the dispersal dynamics of the planktonic stages and the behaviour of the host. Until recently virtually nothing was known about the relationship between the parasite and the host, or how the host may influence lice at local or population level. Typically, impacts on the host have usually been reported in terms of pathological lesions caused by attachment and feeding of the adult stages, as well as localised mild epithelial responses to juvenile attachment. However many studies report pathology associated with severe infestation. Recent new studies on the host-parasite interactions of L. salmonis have shown that this parasite induces stress-related responses systemically in the host skin and gills and that the stress response and immune systems are modulated. In the second part of this review, these new studies are presented, together with results from other host-parasite model systems where data for caligid sea lice are missing. One of the most revealing methods reported recently is the application of a net confinement stressor to examine modulation of the stress response and immune system of the host fish. This approach has shown that although until now, infective stages of L. salmonis were not thought to affect the host, they do induce systematic effects in the host that result in a stress response and modulated immune system. Host-parasite interactions affecting these stress responses and the immune system may be key factors in facilitating epizootics by reducing the host's ability to reject the parasites, as well as reducing disease resistance under some environmental conditions. The host-parasite interaction therefore needs to be incorporated into any model of population structure and dynamics.
鲑鳟鱼虱是鲑科鱼类的一种特定寄生虫，见于大西洋和太平洋。当感染严重时，鱼类会死亡，不过导致疾病流行的因素，尤其是在野生鲑科鱼类种群中的致病因素，在很大程度上仍不为人知。在过去20年里，这种寄生虫给养殖鲑鱼生产造成了重大经济损失，在当地野生鲑科鱼类种群中可能也是如此。了解种群之间的连通性对于理解感染的流行病学以及水产养殖中感染的管理至关重要。来自遗传学、抗药性、幼虫扩散模型以及野生和养殖宿主中感染的时空模式的数据表明，存在一个空间结构高度复杂的集合种群，其组成部分具有不同程度的连通性、灭绝概率以及对局部感染发展的影响。种群结构主要由浮游阶段的扩散动态和宿主的行为决定。直到最近，人们对寄生虫与宿主之间的关系，或者宿主在局部或种群水平上如何影响鱼虱几乎一无所知。通常，对宿主的影响通常是根据成虫附着和取食引起的病理损伤，以及对幼体附着的局部轻度上皮反应来报道的。然而，许多研究报告了与严重感染相关的病理学情况。最近关于鲑鳟鱼虱宿主 - 寄生虫相互作用的新研究表明，这种寄生虫会在宿主皮肤和鳃中全身性地诱导与应激相关的反应，并且应激反应和免疫系统会受到调节。在本综述的第二部分，将介绍这些新研究，以及其他缺乏海鲺数据的宿主 - 寄生虫模型系统的结果。最近报道的最具启发性的方法之一是应用网箱限制应激源来研究宿主鱼类应激反应和免疫系统的调节。这种方法表明，尽管到目前为止，鲑鳟鱼虱的感染阶段被认为不会影响宿主，但它们确实会在宿主中诱导系统性效应，导致应激反应和免疫系统受到调节。影响这些应激反应和免疫系统的宿主 - 寄生虫相互作用可能是通过降低宿主排斥寄生虫的能力以及在某些环境条件下降低抗病性来促进疾病流行的关键因素。因此，宿主 - 寄生虫相互作用需要纳入任何种群结构和动态模型中。
