Heart and Muscle Inflammation (HSMI)

Heart and Skeletal Muscle Inflammation (HSMI) is a significant viral disease affecting farmed Atlantic salmon (Salmo salar). It is caused by the Piscine orthoreovirus (PRV), leading to severe inflammation of the heart and skeletal muscles. First detected in Norway in 1999, HSMI has since been reported in other major salmon farming regions, including Scotland and Canada, causing substantial economic losses. HSMI primarily affects Atlantic salmon but has also been observed in other salmonid species, including rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) 123.

• Physical Signs:

  • Muscle Lesions: Inflammation and degradation of skeletal muscles, often visible as pale or white streaks.
  • Cardiac Damage: Inflammation and damage to the heart muscle, affecting its function.
  • Anemia: Pale gills and organs due to reduced red blood cells.
  • Pericardial Effusion: Accumulation of fluid around the heart.
  • Other Signs: Pale heart, yellow liver, ascites, swollen spleen, and petechiae in the perivisceral fat 12.
• Behavioral Changes:

  • Lethargy: Reduced activity and swimming stamina.
  • Loss of Appetite: Decreased feeding behavior and subsequent weight loss.
  • Abnormal Swimming Patterns: Fish may display erratic or weakened swimming due to muscle damage 13.

Progression of Symptoms

• Early Stages: Subtle signs such as reduced feed intake and slight lethargy.

• Advanced Stages: More pronounced physical symptoms, including muscle lesions and cardiac damage, leading to increased mortality if not managed. Morbidity may be very high, while mortalities are variable and can reach up to 20% in affected cages 123.

• Impact on Fish Health: HSMI severely compromises heart and muscle function, making fish more susceptible to secondary infections and reducing overall vitality.

Etiology

• Causative Agent: Piscine orthoreovirus (PRV) 34.

• Transmission Methods:

  • Direct Contact: Spread between infected and healthy fish through close proximity.
  • Waterborne: The virus can be transmitted through water, potentially spreading from one farm to another 14.

Risk Factors

• Environmental Factors: Poor water quality, high stocking densities, and stressful conditions can increase susceptibility to HSMI.

• Farm Management Practices: Ineffective biosecurity measures and lack of routine health monitoring can facilitate the spread of PRV 14.

Diagnostic Methods

• Clinical Examination: Observation of physical and behavioral symptoms indicative of HSMI.

• Laboratory Tests:

  • PCR (Polymerase Chain Reaction): Detects PRV genetic material in fish tissues.
  • Histopathology: Microscopic examination of heart and muscle tissues to identify characteristic lesions of HSMI.
  • Immunohistochemistry: Detects viral antigens in tissue samples 145.

Differential Diagnosis

• Distinguishing HSMI from Other Diseases: It is crucial to differentiate HSMI from other diseases with similar symptoms, such as Pancreas Disease (PD) and Cardiomyopathy Syndrome (CMS) 123.

Treatment Options

• Current Treatments: There are no effective antiviral treatments available for HSMI. Management focuses on preventing the spread and mitigating the impact through biosecurity measures and supportive care.

• Experimental Treatments: Ongoing research into potential antiviral agents and other therapeutic approaches 134.

Preventive Measures

• Biosecurity Protocols:

  • Implementing strict quarantine measures for new stock to prevent the introduction of PRV.
  • Regular disinfection of equipment and facilities to minimize the risk of contamination.
• Farm Management Practices:

  • Reducing stocking densities to decrease the risk of virus transmission.
  • Regular health monitoring and early detection programs to identify and manage outbreaks promptly.
  • Implementing all-in/all-out stocking practices to reduce the risk of spreading infections 145.

Real-World Examples

• Notable Outbreaks:
  • Norway (1999): The first identified outbreaks led to significant economic losses and increased regulatory scrutiny.

1. "Piscine orthoreovirus (PRV) replicates in Atlantic salmon (Salmo salar L.) erythrocytes ex vivo"
   Authors: Wessel, Ø., et al.
   Reference: Wessel, Ø., et al. (2015). Veterinary Research, 46(1), 26.
   Link to study
2. "Experimental transmission of heart and skeletal muscle inflammation (HSMI) in Atlantic salmon Salmo salar"
   Authors: Kongtorp, R. T., et al.
   Reference: Kongtorp, R. T., et al. (2004). Diseases of Aquatic Organisms, 59(2), 105-112.
   Link to study
3. "Heart and skeletal muscle inflammation (HSMI) disease diagnosed on a British Columbia salmon farm through a longitudinal farm study"
   Authors: Di Cicco, E., et al.
   Reference: Di Cicco, E., et al. (2017). PLOS ONE, 12(2), e0171471.
   Link to study

These studies represent significant advancements in understanding HSMI, its association with PRV, and its geographic distribution. They highlight the ongoing research efforts to better characterize and manage this disease in various salmon-producing regions.

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Title: Heart and Skeletal Muscle Inflammation
Date: 2024-07-12
Tags: #HeartandSkeletalMuscleInflammation, #HSMI, #Salmonoids #Salmon, #AtlanticSalmon, #CohoSalmon #PiscineOrthoreovirus, #PRV, #Trout, #RainbowTrout, #ViralDisease, #Virus