title: Heart and skeletal muscle inflammation (HSMI) disease diagnosed on a British Columbia salmon farm through a longitudinal farm study.
abstract: Heart and skeletal muscle inflammation (HSMI) is an emerging disease of marine-farmed Atlantic Salmon (Salmo salar), first recognized in 1999 in Norway, and later also reported in Scotland and Chile. We undertook a longitudinal study involving health evaluation over an entire marine production cycle on one salmon farm in British Columbia (Canada). In previous production cycles at this farm site and others in the vicinity, cardiac lesions not linked to a specific infectious agent or disease were identified. Histologic assessments of both live and moribund fish samples collected at the farm during the longitudinal study documented at the population level the development, peak, and recovery phases of HSMI. The fish underwent histopathological evaluation of all tissues, Twort's Gram staining, immunohistochemistry, and molecular quantification in heart tissue of 44 agents known or suspected to cause disease in salmon. Our analysis showed evidence of HSMI histopathological lesions over an 11-month timespan, with the prevalence of lesions peaking at 80-100% in sampled fish, despite mild clinical signs with no associated elevation in mortalities reported at the farm level. Diffuse mononuclear inflammation and myodegeneration, consistent with HSMI, was the predominant histologic observation in affected heart and skeletal muscle. Infective agent monitoring identified three agents at high prevalence in salmon heart tissue, including Piscine orthoreovirus (PRV), and parasites Paranucleospora theridion and Kudoa thyrsites. However, PRV alone was statistically correlated with the occurrence and severity of histopathological lesions in the heart. Immunohistochemical staining further localized PRV throughout HSMI development, with the virus found mainly within red blood cells in early cases, moving into the cardiomyocytes within or, more often, on the periphery of the inflammatory reaction during the peak disease, and reducing to low or undetectable levels later in the production cycle. This study represents the first longitudinal assessment of HSMI in a salmon farm in British Columbia, providing new insights on the pathogenesis of the disease.
authors.affiliation: Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, British Columbia, Canada.|Pacific Salmon Foundation, Vancouver, British Columbia, Canada.
authors.forename: Emiliano
authors.identifier: http://orcid.org/0000-0002-2462-5190
authors.initials: E
authors.lastname: Di Cicco
authors.affiliation: School of Veterinary Medicine, St. George's University, Grenada, W. Indies.
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Ferguson
authors.affiliation: Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, British Columbia, Canada.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Schulze
authors.affiliation: Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, British Columbia, Canada.
authors.forename: Karia H
authors.initials: KH
authors.lastname: Kaukinen
authors.affiliation: Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, British Columbia, Canada.
authors.forename: Shaorong
authors.initials: S
authors.lastname: Li
authors.affiliation: Centre for Veterinary Epidemiological Research, Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Vanderstichel
authors.affiliation: Department of Food Safety and Infection Biology, Norwegian University of Life Sciences, Oslo, Norway.
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Wessel
authors.affiliation: Department of Food Safety and Infection Biology, Norwegian University of Life Sciences, Oslo, Norway.
authors.forename: Espen
authors.initials: E
authors.lastname: Rimstad
authors.affiliation: Centre for Veterinary Epidemiological Research, Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Gardner
authors.affiliation: Centre for Veterinary Epidemiological Research, Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada.
authors.forename: K Larry
authors.initials: KL
authors.lastname: Hammell
authors.affiliation: Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, British Columbia, Canada.
authors.forename: Kristina M
authors.initials: KM
authors.lastname: Miller
mesh_terms: D000818:Animals; D001955:British Columbia; D009202:Cardiomyopathies / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D005393:Fish Diseases / Q000473:pathology* / Q000821:virology; D005398:Fisheries; D007249:Inflammation / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D008137:Longitudinal Studies; D012088:Reoviridae Infections / Q000473:pathology / Q000662:veterinary* / Q000821:virology; D020317:Salmo salar / Q000821:virology*