Table 2 Nature and frequency1 of significant histopathology lesions in tissues of Atlantic salmon affected with heart and skeletal muscle inflammation (HSMI) and coho salmon affected with HSMI-like disease
Tissue | Atlantic salmon | Coho salmon | ||||||
|---|---|---|---|---|---|---|---|---|
Histopathological description | Diagnosis | Frequency | Histopathological description | Diagnosis | Frequency | |||
Heart | Epicardium | Multifocal to diffuse infiltration of mononuclear cells. | Mononuclear epicarditis, subacute, multifocal to diffuse, moderate to severe. | 33/36 | Multifocal to diffuse infiltration of mononuclear cells. | Mononuclear epicarditis, subacute, multifocal to diffuse, moderate to severe. | 18/18 | |
Myocardium | Spongy layer | Multifocal to diffuse infiltration of mononuclear cells of spongy layer and compact layer. Multifocal to diffuse myocardial degeneration & necrosis. | Mononuclear myocarditis, degenerative, necrotic, subacute to chronic, multifocal to diffuse, moderate to severe. | 33/36 | Multifocal to diffuse infiltration of mononuclear cells of spongy layer. Some mononuclear cells are present in the compact layer. Focal to multifocal myocardial degeneration & necrosis. | Mononuclear myocarditis, degenerative, necrotic, subacute to chronic, multifocal to diffuse, moderate to severe. | 15/18 | |
Compact layer | Not significant findings | |||||||
Red muscle | Multifocal to diffuse infiltration of mononuclear cells in red muscle. Multifocal to diffuse myocytic degeneration & necrosis. | Mononuclear myocarditis, degenerative, necrotic, subacute to chronic, Multifocal to diffuse, moderate to severe. | 30/36 | Multifocal to diffuse infiltration of mononuclear cells in red muscle. | Mononuclear myocarditis, Multifocal to diffuse, mild to moderate. | 12/18 | ||
Liver | Blood vessels surrounded by a mononuclear cell infiltrate. Degeneration, necrotic, hemorrhagic, acute to subacute, focal to multifocal, moderate to severe. | Mononuclear hepatitis, necrotic, hemorrhagic, acute to subacute, focal to multifocal, moderate to severe. | 16/36 | Blood vessels surrounded by a mononuclear cell infiltrate. Degeneration, necrotic, acute to subacute, focal to multifocal, mild to moderate. | Mononuclear perivascular hepatitis, necrotic, acute to subacute, focal to multifocal, mild to moderate. | 14/18 | ||
Tissue | Atlantic salmon | Coho salmon | ||||||
Histopathological description | Diagnosis | Frequency | Histopathological description | Diagnosis | Frequency | |||
Spleen | Diffuse infiltration of mononuclear cells, interstitial. Diffuse congestion with evidence of increase in circulating granulocytes & intravascular erythrophagia. | Splenitis, subacute, diffuse, moderate. | 11/36 | Diffuse infiltration of mononuclear cells, interstitial. Diffuse congestion with evidence of increase in circulating granulocytes & intravascular erythrophagia. | Splenitis, subacute, diffuse, moderate. | 10/18 | ||
Kidney | Diffuse infiltration of mononuclear cells, interstitial. | Interstitial nephritis, subacute, diffuse, moderate. | 4/36 | Diffuse infiltration of mononuclear cells, interstitial. | Interstitial nephritis, subacute, diffuse, moderate. | 11/18 | ||
Pyloric caeca | Extensive proliferation of fibroblasts-like cells, mononuclear, eosinophilic cells with eccentric nucleus & macrophage-like cells. Large empty vacuoles adjacent to the pancreatic area observed in some cases. | Vaccine induced peritonitis | 11/36 | No significant findings. | No significant findings. | 18/18 | ||
Gill | Lamellar fusion across multiple filaments. | Branchiosis multifocal, moderate. | 3/36 | Lamellar fusion across multiple filaments. Numerous interlamellar vesicle formation. Neoparamoeba perurans showing nucleus & “parasome". Granular eosinophilic intracytoplasmic inclusions in hypertrophied epithelial cells. | Focal to multifocal bacterial & parasitic hyperplasia, subacute to chronic, moderate to severe, with Paramoeba perurans & epitheliocystis-like inclusions. | 16/18 | ||
Posterior gut | Multifocal to diffuse infiltration of mononuclear cells in lamina propria & sub mucosa. | Mononuclear enteritis, multifocal to diffuse, moderate. | 5/36 | Multifocal to diffuse infiltration of mononuclear cells in lamina propria & sub mucosa. | Mononuclear enteritis, multifocal to diffuse, moderate. | 4/18 | ||