The viral hemorrhage disease caused by grass carp reovirus (GCRV) is a serious contagious disease of grass carp that mainly infects fingerlings and yearlings. Epidemiological studies have shown that GCRV genotype II is currently the prominent genotype. However, little is known about the histopathological characteristics, virus distribution, and expression of immunity-related genes in grass carp infected by GCRV genotype II. In this study, we found that grass carp infected by GCRV genotype II lost appetite, swam alone, and rolled, and their fins, eyes, operculum, oral cavity, abdomen, intestine, and muscles showed pronounced punctate hemorrhage. Congestion, swelling, deformation, thinning of membranes, dilatation and darkened color of nucleoli, cathepsis, erythrocyte infiltration, and vacuole formation were observed in some infected tissues. A qRT-PCR test showed that the 11 genome segments of GCRV had similar expression patterns in different tissues. The S8 segment, with unknown function and no homologous sequences, had the highest expression level, while the most conserved segment, L2, had the lowest expression level. GCRV particles were distributed in different tissues, especially in the intestine. In the infected intestine, the expression of various receptors and adaptor molecules was modulated at different levels. Pro-inflammatory cytokine interleukin-1β (IL-1β) expression was 2160.9 times higher than that in the control group. The upregulation of immunity-related genes activated the antiviral immunity pathways. Therefore, the intestine might play a dual role in mediating GCRV infection and the antiviral immune response. This study provides detailed information about the pathogenicity of GCRV and expression of immunity-related genes, laying the foundation for further research on virus control and treatment.

中文翻译：

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草鱼感染基因型II型草鱼呼肠孤病毒后临床症状、病毒分布及几种抗病毒免疫相关基因mRNA表达的研究

草鱼呼肠孤病毒（GCRV）引起的病毒性出血病是草鱼的一种严重传染性疾病，主要感染鱼种和一岁鱼。流行病学研究表明，GCRV基因型II是目前最主要的基因型。然而，对于GCRV基因型II感染草鱼的组织病理学特征、病毒分布和免疫相关基因的表达知之甚少。在本研究中，我们发现感染GCRV基因型II的草鱼食欲不振、独游、翻滚，鱼鳍、眼睛、鳃盖、口腔、腹部、肠道和肌肉出现明显的点状出血。部分感染组织充血、肿胀、变形、膜变薄、核仁扩张、颜色变深、组织坏死、红细胞浸润、空泡形成。qRT-PCR测试显示GCRV的11个基因组片段在不同组织中具有相似的表达模式。功能未知、无同源序列的S8片段表达量最高，而最保守的片段L2表达量最低。GCRV颗粒分布在不同的组织中，特别是在肠道中。在受感染的肠道中，各种受体和接头分子的表达受到不同水平的调节。促炎细胞因子白介素1β（IL-1β）表达较对照组升高2160.9倍。免疫相关基因的上调激活了抗病毒免疫途径。因此，肠道可能在介导 GCRV 感染和抗病毒免疫反应中发挥双重作用。该研究提供了GCRV致病性和免疫相关基因表达的详细信息，为进一步研究病毒控制和治疗奠定了基础。