Heart and Skeletal Muscle Inflammation (HSMI)
Cardiovascular System, Musculoskeletal System

Heart and Skeletal Muscle Inflammation (HSMI) – Histopathology

by Carlos Sandoval

Heart and skeletal muscle inflammation (HSMI) is an emerging disease of marine-farmed Atlantic salmon (Salmo salar L), first recognized in 1999 in Norway, and later also reported in Scotland, Chile and Canada.

Atlantic salmon, heart, with severe diffuse epicarditis, H&E.
Figure 1. Atlantic salmon, heart, with severe diffuse epicarditis, H&E.

HSMI is transmissible and, the weight of recent evidence supports the contention that the cause is an Orthoreovirus with the proposed name Piscine orthoreovirus (PRV).

Atlantic salmon, liver with coagulative hepatic necrosis due to ischaemia, H&E.
Figure 2. Atlantic salmon, liver with coagulative hepatic necrosis due to ischaemia, H&E.









This virus has not yet been cultured in vitro, thereby hampering traditional experimental reproduction of the disease.

Atlantic salmon, heart with inflammatory infiltrate in compact ventricular myocardium. H&E.
Figure 3. Atlantic salmon, heart with inflammatory infiltrate in compact ventricular myocardium. H&E.



As the name of the disease suggests, major changes in HSMI involve the heart and red skeletal muscle where extensive inflammation and multifocal degeneration of myocytes are evident.

Liver is also frequently involved, a consequence of hypoxia due to failing cardiovascular output.

Atlantic salmon, red skeletal muscle, with moderate multifocal myosistis, H&E.
Figure 4. Atlantic salmon, red skeletal muscle, with moderate multifocal myosistis, H&E.








Histological findings include epicarditis, myocarditis and myositis (red muscle). In the liver, zonal coagulative hepatic necrosis can be observed.

Atlantic salmon with HSMI. Note severe inflammation and loss of mainly red muscle fibres. Loss of white fibres may be virus-related, but can also be cachexia, as the animals lose appetite and are less able to swim properly.
Figure 5. Atlantic salmon with HSMI. Note severe inflammation and loss of mainly red muscle fibres. Loss of white fibres may be virus-related, but can also be cachexia, as the animals lose appetite and are less able to swim properly.

















REFERENCES

  • Di Cicco, E., Ferguson, H. W., Schulze, A. D., Kaukinen, K. H., Li, S., Vanderstichel, R., … & Miller, K. M. (2017). Heart and skeletal muscle inflammation (HSMI) disease diagnosed on a British Columbia salmon farm through a longitudinal farm study. PLoS One, 12(2).
  • Kongtorp, R. T., Taksdal, T., and Lyngoy, A. 2004b.Pathology of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon Salmo salar. Diseases of Aquatic Organisms, 59: 217–224.
  • Yousaf, M. N., & Powell, M. D. (2012). The effects of heart and skeletal muscle inflammation and cardiomyopathy syndrome on creatine kinase and lactate dehydrogenase levels in Atlantic salmon (Salmo salar L.). The Scientific World Journal, 2012.

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By: Carlos Sandoval

Carlos Sandoval Hurtado is a Veterinary doctor at Universidad Católica de Temuco, Masters in Science, specializing in Animal Health at Universidad Austral de Chile. He has over 15 years experience in the area of pathology and histopathology of fish and other species, becoming one of the most renowned histopathologists in Chile. He is currently the Director of VeHiCe (Veterinary Histopathology Center) a leading laboratory in histopathology whose clients include laboratories, universities, aquaculture industry and avian industry mainly.

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