Characterization of myocardial lesions associated with cardiomyopathy syndrome in Atlantic salmon, Salmo salar L., using laser capture microdissection

Abstract

Cardiomyopathy syndrome (CMS) in Atlantic salmon, Salmo salar L., is characterized by focal infiltration in the spongy myocardium and endocardium of the heart. The origin of the mononuclear infiltrate is unknown. Using experimentally infected fish, we investigated localization of the causative agent, piscine myocarditis virus (PMCV), within the heart and characterized the cell population associated with myocardial lesions. Cellular and transcriptional characteristics in the lesions were compared with adjacent non-infiltrated tissues using laser capture microdissection, RT-qPCR and immunohistochemistry. Our results reveal that PMCV is almost exclusively present in myocardial lesions. The inflammatory infiltrate comprises a variety of leucocyte populations, including T cells, B cells, MHC class II(+) and CD83(+) cells, most likely of the macrophage line. Correlation analyses demonstrated co-ordinated leucocyte activity at the site of the virus infection. Cellular proliferation and/or DNA repair was demonstrated within the myocardial lesions. Different cell populations, mainly myocytes, stained positive for proliferating cell nuclear antigen (PCNA). Densities of endothelial cells and fibroblasts were not significantly increased. The simultaneous presence of PMCV and various inflammatory cells in all myocardial lesions analysed may indicate that both viral lytic and immunopathological effects may contribute to the pathogenesis of CMS.

Cardiomyopathy syndrome in Atlantic salmon Salmo salar L.: A review of the current state of knowledge

“…CMS outbreaks and CMS‐related pathological lesions have not been described in hatcheries, but PMCV has been found in low quantities at this stage of the production (Wiik‐Nielsen, Lovoll, et al., ).…”

“…In a previous study, the prevalence of viral RNA from both piscine orthoreovirus (PRV) and PMCV in Atlantic salmon broodfish and progeny was investigated by real‐time PCR (Wiik‐Nielsen, Lovoll, et al., ). RNA sequences from PMCV were detected in heart (Ct 24) and spleen (Ct 22) of approximately 80 % of the broodfish before stripping.…”

Whole-genome analysis of piscine reovirus (PRV) shows PRV represents a new genus in family Reoviridae and its genome segment S1 sequences group it into two separate sub-genotypes

“…Most recently, it has been reported that serum enzymes creatine kinase and lactate dehydrogenase, associated with cardiac injury in humans [21], are significantly correlated with HSMI histopathology in Atlantic salmon [22]. Other reports doubt the pathogenicity of PRV, describing PRV as an opportunistic virus [23,24] or non-pathogenic virus [15]. The virus has been detected in marine-farmed Atlantic salmon in Chile [25,26].…”

“…To date only two “isolates”, both from marine-farmed Atlantic salmon from Norway, have been sequenced on all 10 genomic segments by high-throughput pyrosequencing of clinical samples: Reovirus sp. Salmo/GP-2010/NOR from HSMI [2], and CMS PRV from a CMS outbreak [24]. However, only the Salmo/GP-2010/NOR sequences are accessible from the GenBank Database (GenBank accession numbers GU994013-GU994022).…”

Pathological pigmentation in cardiac tissues of Atlantic salmon (Salmo salar L.) with cardiomyopathy syndrome

“…During this study, an unforeseen outbreak of pancreatic necrosis (IPN) was observed in some of the challenged fish [3]. Furthermore, piscine reovirus (PRV) was also detected in the material [16]. The lesions are therefore referred to as CMS-associated pathological changes in PMCV-positive fish co-infected by IPNV and PRV.…”