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Cardiomyopathy Syndrome, a significant viral disease of Atlantic salmon

Atlantic salmon is a highly valued aquaculture product. Scotland is the third-largest producer of Atlantic salmon after Norway and Chile, and Atlantic salmon is the largest food export for both Scotland and the UK, with an annual value worth £640 million. The industry also has an important social impact by creating over 3000 jobs directly related to fish production in many of the remote regions of Scotland, including Orkney, Shetland and the Hebrides. In 2019, 203,881 tonnes of Atlantic salmon were produced in Scotland, representing an increase of 30 % on the previous year’s production. According to Salmon Scotland, more than £485 million worth of Atlantic salmon was exported in the first three quarters of 2021, exceeding all the exports in 2020.

Over the last 15 years, the industry has seen an increase in viral cardiomyopathies. These include pancreas disease (PD) caused by salmonid alphavirus (SAV), cardiomyopathy syndrome (CMS) caused by piscine myocarditis virus (PMCV), and heart and skeletal muscle inflammation (HSMI) caused by piscine orthoreovirus (PRV). These viruses can be present as co-infections and lead to lesions in both the myocardium of the heart and/or skeletal muscle. In Norway, the world’s largest Atlantic salmon producer, these viral cardiomyopathies have been identified as the three most important viral diseases for Atlantic salmon production, with CMS and HSMI as the second and third most important cause of economic loss to the industry after sea lice. PD is the only disease for which there is a commercial vaccine, which has lowered the economic impact of this disease. In Scotland, cases of HSMI are less frequently reported and CMS is regarded as the second most important disease after sea lice. The biggest economic impact of CMS comes from the sudden death of fish due to heart failure in apparently healthy harvest-sized fish.

Knowledge relating to PMCV is limited because it is very difficult to culture in the laboratory. This has prevented the development of an inactivated vaccine and hampered research related to this pathogen. The only tools available currently for salmon farmers are mitigation strategies to reduce stock losses that include reducing handling and stocking densities of the fish.  Early diagnosis of CMS is vital to allow salmon producers to take steps to avoid losses during the late stages of the production cycle. Currently, diagnosis of CMS is based on clinical signs, histopathology and RT-qPCR, which require lethal sampling of valuable, market-size fish.

The identification of proteins present in the serum of fish with CMS may be a useful indicator of early stages of the disease. In human and veterinary medicine, cardiac diseases are detected with cardiac biomarkers, measured using commercial serological tests. These types of tests are almost non-existent for aquaculture. Knowledge of biomarkers associated with cardiac disease in Atlantic salmon is limited, but is essential for the development of serological tools to detect cardiac disease in farmed fish.

The Aquaculture Research Group at Moredun Research Institute and Cooke Aquaculture Scotland collaborated to increase knowledge and understanding in this area, assessing the suitability of commercially available troponin (involved in muscle contraction) detection kits and identifying novel cardiac biomarkers. The commercially available kits tested proved unsuitable for this purpose and there was a requirement to identify and develop new biomarker tests for cardiomyopathies in Atlantic salmon. We obtained funding from the Scottish Aquaculture Innovation Centre (SAIC) to do this with involvement from additional scientists at the Royal Dick Vet School at Edinburgh, Life Diagnostic Ltd., a leading company developing serology tests for veterinary biomarkers, and Benchmark Genetics, a leading aquaculture breeding company. We identified a panel of potential cardiac biomarkers for the identification of CMS that were tested using both field samples and samples from experimentally infected fish.

In our current follow-on project, also funded by SAIC, we are assessing if these markers can identify early-stage CMS in the field (during the production cycle) and to see if they can be used to differential diagnose other cardiomyopathies (PD and HSMI). Scientists at University of Glasgow have joined our consortium to help us validate the use of these biomarkers.

We also performed proteomic and genomic analysis on sera and heart samples from PMCV–infected fish, respectively, with the aim of increasing our understanding of the immunological and physiological responses of Atlantic salmon to PMCV infection and to identify additional biomarkers to create a comprehensive serological diagnostic panel for cardiomyopathies in Atlantic salmon.

For more information, please contact Janina Costa [email protected]

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