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Abstract：
Heterogeneity in immunity occurs across numerous disease systems with individuals from the same population having diverse disease outcomes. Proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae, is a persistent parasitic disease negatively impacting both wild and farmed salmonids. Little is known of how PKD is spread or maintained within wild susceptible populations. We investigated an aspect of fish disease that has been largely overlooked, that is, the role of the host phenotypic heterogeneity in disease outcome. We examined how host susceptibility to T. bryosalmonae infection, and the disease PKD, varied across different infection life-history stages and how it differs between naïve, re-infected and persistently infected hosts. We investigated the response to parasite exposure in host phenotypes with (a) different ages and (b) heterogeneous infection life histories. Among (a) the age phenotypes were young-of-the-year (YOY) fish and juvenile 1+ fish (fish older than one) and, for (b) juvenile 1+ infection survivors were either re-exposed or not re- exposed to the parasite and response phenotypes were assigned post-hoc dependant on infection status. In fish not re-exposed this included fish that cleared infection (CI) or had a persistent infection (PI). In fish re-exposed these included fish that were re-infected (RI), or re-exposed and uninfected (RCI). We assessed both parasite-centric (infection prevalence, parasite burden, malacospore transmission) and host-centric parameters (growth rates, disease severity, infection tolerance and the immune response). In (a), YOY fish, parasite success and disease severity were greater and differences in the immune response occurred, demonstrating an ontogenetic decline of susceptibility in older fish. In (b), in PI and RI fish, parasite success and disease severity were comparable. However, expression of several adaptive immunity markers was greater in RI fish, indicating concomitant immunity, as re-exposure did not intensify infection. We demonstrate the relevance of heterogeneity in infection life history on disease outcome and describe several distinctive features of immune ontogeny and protective immunity in this model not previously reported. The relevance of such themes on a population level requires greater research in many aquatic disease systems to generate clearer framework for understanding the spread and maintenance of aquatic pathogens.
摘要：
免疫的异质性发生在许多疾病系统中，来自同一人群的个体具有不同的疾病结果。苔藓四肽引起的增殖性肾脏疾病（PKD），是一种持续的寄生虫病，对野生和养殖的鲑鱼都产生了负面影响。对PKD如何在野生易感人群中传播或维持知之甚少。我们调查了大部分被忽视的鱼类疾病的一个方面，也就是说,宿主表型异质性在疾病结局中的作用。我们检查了宿主对苔藓沙门氏菌感染的易感性，疾病PKD，不同的感染生活史阶段，以及幼稚之间的差异，重新感染和持续感染的宿主。我们调查了（a）不同年龄和（b）异质性感染生活史的宿主表型对寄生虫暴露的反应。在（a）年龄表型中，是年幼鱼（YOY）和幼鱼1（年龄超过1岁的鱼），对于(b)幼年1+感染的幸存者要么重新暴露于寄生虫，要么不重新暴露于寄生虫，反应表型根据感染状态进行事后分配。在未重新暴露的鱼中，这包括清除感染（CI）或持续感染（PI）的鱼。在重新暴露的鱼类中，这些包括重新感染的鱼类(RI)，或重新暴露和未感染（RCI）。我们评估了两种以寄生虫为中心的(感染患病率，寄生虫负担,malacospore传播)和以寄主为中心的参数(生长速率，疾病严重程度,感染耐受性和免疫反应)。在（a）中，YOY鱼,寄生虫成功和疾病严重程度更大，免疫反应发生了差异，表明老年鱼类易感性的个体发育下降。在(b)中，在PI和RI鱼中，寄生虫成功和疾病严重程度相当。然而,几种适应性免疫标记在RI鱼中的表达更高，表明伴随免疫，因为再次暴露并没有加剧感染.我们证明了感染生活史的异质性与疾病结果的相关性，并描述了该模型中先前未报道的免疫个体发育和保护性免疫的几个独特特征。这些主题在人口水平上的相关性需要在许多水生疾病系统中进行更多的研究，以产生更清晰的框架来了解水生病原体的传播和维持。
