Figure 2. Salmon with CMS. Necrosis in the atrium of this fish has been so severe that it has ruptured. Note that the ventricle appears normal, due only to the fact that the compact layer remains largely unaffected.

Cardiomyopathy syndrome (CMS) – Gross Pathology

Cardiomyopathy syndrome (CMS), is a severe heart disease of Atlantic salmon.  This transmissible condition has been diagnosed in several countries, especially Norway, where it was first reported, but also Scotland, Ireland and the Faroes. It is causally linked to the Piscine Myocarditis Virus (PMCV), closely allied to the Totiviridae. Typically, CMS occurs in the biggest, fastest-growing fish that never go off their feed – indeed their stomach is usually full of pellets when they suddenly die! Brood stock are also susceptible.

Figure 1. Cardiomyopathy syndrome in large Atlantic salmon. The sinus venosus in this fish has ruptured, leading to a blood-filled peritoneal cavity.
Figure 1. Cardiomyopathy syndrome in large Atlantic salmon. The sinus venosus in this fish has ruptured, leading to a blood-filled peritoneal cavity.

This disease has an especially significant economic impact as it primarily affects large fish.

Gross lesions include exophthalmia and other changes expected with a failing heart, especially zonal hepatic pallor/congestion.

Figure 2. Salmon with CMS. Necrosis in the atrium of this fish has been so severe that it has ruptured. Note that the ventricle appears normal, due only to the fact that the compact layer remains largely unaffected.
Figure 2. Salmon with CMS. Necrosis in the atrium of this fish has been so severe that it has ruptured. Note that the ventricle appears normal, due only to the fact that the compact layer remains largely unaffected.











More dramatically, the sinus venosus or atrium can rupture, leading to a blood-filled pericardial sac or even peritoneal cavity.

Histopathologically, the lesions are by-and-large restricted to the spongy myocardium – the compact layer of the ventricle is mostly normal. Necrosis of the spongy layer can be so severe, especially in the atrium, that it can rupture. Skeletal muscle and pancreas are largely normal, and this can help differentiate CMS from other viral diseases of salmon in which myocarditis is a feature, such as Heart and skeletal muscle inflammation (HSMI) or Pancreas disease (PD).

Figure 3. Atlantic salmon with HSMI. Note the zonal liver lesions, a result of failing circulation, and resulting hypoxia. The gross lesions in HSMI and CMS can be similar, except that there are no skeletal muscle lesions in CMS, and the heart lesions largely avoid compact myocardium.
Figure 3. Atlantic salmon with HSMI. Note the zonal liver lesions, a result of failing circulation, and resulting hypoxia. The gross lesions in HSMI and CMS can be similar, except that there are no skeletal muscle lesions in CMS, and the heart lesions largely avoid compact myocardium.

The picture becomes more complicated if more than one virus disease is present at the same time! Recovering phases of HSMI can also often resemble CMS.

Skeletal muscle and pancreas are largely normal, and this can help differentiate CMS from other viral diseases of salmon in which myocarditis is a feature, such as Heart and skeletal muscle inflammation (HSMI) or Pancreas disease (PD).

The picture becomes more complicated if more than one virus disease is present at the same time! Recovering phases of HSMI can also often resemble CMS.







REFERENCES

  • Ferguson, H.W., T. Poppe, and D.J. Speare.  (1990). Cardiomyopathy syndrome in farmed Norwegian salmon Salmo salar L.  Dis. Aquat. Orgs. 8:225-231.
  • Lovoll, M., Wiik‐Nielsen, J., Grove, S., Wiik‐Nielsen, C. R., Kristoffersen, A. B., Faller, R. & Tengs, T. (2010). A novel totivirus and piscine reovirus (PRV) in Atlantic salmon (Salmo salar) with cardiomyopathy syndrome (CMS). Virology Journal, 7, 309. https://doi.org/10.1186/1743-422X-7-309
  • Wiik‐Nielsen, C. R., Ski, P. M. R., Aunsmo, A., & Lovoll, M. (2012). Prevalence of viral RNA from piscine reovirus and piscine myocarditis virus in Atlantic salmon, Salmo salar L., broodfish and progeny. J. Fish Diseases, 35, 169–171. https://doi.org/10.1111/j.1365-2761.2011.01328.x

By: Hugh Ferguson

Dr Ferguson earned his veterinary degree from the Royal (Dick) School of Veterinary Studies, Edinburgh, Scotland and held a Wellcome Research Fellowship at the Institute of Aquaculture, Stirling University where he obtained his PhD. He subsequently worked for 4 years as a diagnostic pathologist at the Veterinary Research Laboratories, Belfast, Northern Ireland, prior to moving to Canada. He is board-certified in the American college of veterinary pathology (ACVP), and is a Fellow of the Royal College of Pathologists (FRCPath, London). Dr Ferguson is currently professor of veterinary pathology, and Senior Research Fellow in Windward Islands Research and Education Foundation (WINDREF), St George’s University (SGU), Grenada, West Indies.

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