Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, V9T 6N7, Canada.
Animal Health Centre, Ministry of Agriculture, Abbotsford, V3G 2M3, Canada.
Sci Rep. 2019 Mar 13;9(1):3297. doi: 10.1038/s41598-019-40025-7.
Piscine orthoreovirus (PRV) is ubiquitous in farmed Atlantic salmon and sometimes associated with disease - most notably, Heart and Skeletal Muscle Inflammation (HSMI). However, PRV is also widespread in non-diseased fish, particularly in Pacific Canada, where few cases of severe heart inflammation have been documented. To better understand the mechanisms behind PRV-associated disease, this study investigated the infection dynamics of PRV from Pacific Canada and the potential for experimental passage of putatively associated heart inflammation in Pacific-adapted Mowi-McConnell Atlantic salmon. Regardless of the PRV source (fish with or without HSMI-like heart inflammation), infections led to high-load viremia that induced only minor focal heart inflammation without significant transcriptional induction of inflammatory cytokines. Repeated screening of PRV dsRNA/ssRNA along with histopathology and gene expression analysis of host blood and heart tissues identified three distinct phases of infection: (1) early systemic dissemination and replication without host recognition; (2) peak replication, erythrocyte inclusion body formation and load-dependent host recognition; (3) long-term, high-load viral persistence with limited replication or host recognition sometimes accompanied by minor heart inflammation. These findings contrast previous challenge trials with PRV from Norway that induced severe heart inflammation and indicate that strain and/or host specific factors are necessary to initiate PRV-associated disease.
养殖大西洋三文鱼中普遍存在鳜鱼虹彩病毒（PRV），有时与疾病相关 - 尤其是心脏和骨骼肌炎症（HSMI）。然而，PRV 在非患病鱼类中也广泛存在，特别是在太平洋加拿大，那里记录的严重心脏炎症病例很少。为了更好地了解 PRV 相关疾病的机制，本研究调查了来自太平洋加拿大的 PRV 的感染动态，以及在太平洋适应型挪威海产养殖三文鱼中进行疑似相关心脏炎症的实验性传代的可能性。无论 PRV 的来源（是否存在 HSMI 样心脏炎症的鱼类）如何，感染都会导致高病毒血症，仅引起轻微的局灶性心脏炎症，而不会引起炎症细胞因子的显著转录诱导。对 PRV dsRNA/ssRNA 进行反复筛查，以及对宿主血液和心脏组织进行组织病理学和基因表达分析，确定了感染的三个不同阶段：（1）早期系统性传播和复制，而宿主未被识别；（2）高峰期复制、红细胞包涵体形成和依赖负荷的宿主识别；（3）长期、高负荷的病毒持续存在，复制或宿主识别有限，有时伴有轻微的心脏炎症。这些发现与先前用来自挪威的 PRV 进行的挑战试验形成对比，后者诱导了严重的心脏炎症，并表明需要特定的毒株和/或宿主因素来引发 PRV 相关疾病。
