Detection of a nodavirus-like agent in heart tissue from reared Atlantic salmon Salmo salar suffering from cardiac myopathy syndrome (CMS)

The present study shows that a nodavirus-like agent is associated with the lesions of cardiac myopathy syndrome (CMS), a disease of unknown etiology which affects reared adult Atlantic salmon Salmo salar. In archive paraffin-embedded heart tissue from Atlantic salmon diagnosed as suffering from CMS, a distinct immunohistochemical reaction was observed when using a primary antibody against striped jack nervous necrosis virus (Nodaviridae). Immunolabeling was detected in the mesothelium and hypercellular lesions of the epicardium and in endothelial cells and myocytes within mild multifocal lesions of the atrial and ventricular trabeculae. Transmission electron microscopy, per formed on deparaffinized samples of the same tissue blocks, revealed substantial amounts of virus-like particles (VLP) in the cytoplasm of endocardial endothelium, in myocytes and in mesothelial cells of the epicardium. The VLP were isometric, spherical and unenveloped, with mean capsid diameters of approximately 25 nm, resembling a virus belonging to the Nodaviridae.