1
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Bjørgen H, Brimsholm M, Lund M, Dahle MK, Rimstad E, Koppang EO. Red and melanized focal changes in the white skeletal muscle of farmed rainbow trout Oncorhynchus mykiss. DISEASES OF AQUATIC ORGANISMS 2024; 158:201-213. [PMID: 38934260 DOI: 10.3354/dao03797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/28/2024]
Abstract
Fillet discoloration by red and melanized focal changes (RFCs and MFCs) is common in farmed Atlantic salmon Salmo salar. In farmed rainbow trout Oncorhynchus mykiss, similar changes have been noted, but their prevalence and histological characteristics have not been investigated. Thus, we conducted a study encompassing 1293 rainbow trout from 3 different farm sites in Norway, all examined at the time of slaughter. Both macroscopic and histological assessments of the changes were performed. Reverse transcription (RT)-qPCR analyses and in situ hybridization (ISH) were used to detect the presence and location, respectively, of potential viruses. Only 1 RFC was detected in a single fillet, while the prevalence of MFCs ranged from 1.46 to 6.47% between populations. The changes were predominantly localized in the cranioventral region of the fillet. Histological examinations unveiled necrotic myocytes, fibrosis, and regeneration of myocytes. Melano-macrophages were found in the affected areas and in myoseptal adipose tissue. Organized granulomas were observed in only 1 fish. Notably, the presence of inflammatory cells, including melano-macrophages, appeared lower compared to what has been previously documented in Atlantic salmon MFCs. Instead, fibrosis and regeneration dominated. RT-qPCR and ISH revealed the presence of piscine orthoreovirus 1 (PRV-1) and salmonid alphavirus (SAV) in skeletal muscle. However, these viruses were not consistently associated with lesioned areas, contrasting previous findings in Atlantic salmon. In conclusion, rainbow trout develop MFCs of a different character than farmed Atlantic salmon, and we speculate whether the observed pathological differences are contributing to their reduced occurrence in farmed rainbow trout.
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Affiliation(s)
- Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Morten Lund
- Pure Salmon Kaldnes, 3241 Sandefjord, Norway
| | | | - Espen Rimstad
- Unit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
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2
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Takano T, Miwa S, Matsuyama T, Kiryu I, Honjo M, Sakai T, Matsuura Y, Yamasaki M, Kumagai A, Nakayasu C. Clinical symptoms and histopathological changes in coho salmon affected by the erythrocytic inclusion body syndrome (EIBS) are caused by the infection of piscine orthoreovirus 2 (PRV-2). JOURNAL OF FISH DISEASES 2024; 47:e13939. [PMID: 38481093 DOI: 10.1111/jfd.13939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 02/29/2024] [Accepted: 03/01/2024] [Indexed: 05/12/2024]
Abstract
The relationship of histopathological changes and the infection of Piscine orthoreovirus 2 (PRV-2) was investigated in coho salmon that were suffering from the erythrocytic inclusion body syndrome (EIBS). Immunohistochemical observations revealed abundant σ1 protein of PRV-2 in the spongy layer of the ventricle of the heart, where severe myocarditis was observed. In the spleen, the virus protein was detected in many erythrocytes, some of which were spherical-shaped and apparently dead. The number of erythrocytes was decreased in the spleen compared to the apparently healthy fish. The virus protein was also detected in some erythrocytes in blood vessels. The viral protein was often detected in many macrophages ingesting erythrocytes or dead cell debris in the spleen or in the kidney sinusoids. Large amounts of the viral genomic segment L2 were also detected in these organs by RT-qPCR. Many necrotic foci were found in the liver, although the virus protein was not detected in the hepatocytes. These results suggest that the primary targets of PRV-2 are myocardial cells and erythrocytes and that clinical symptoms such as anaemia or jaundice and histopathological changes such as myocarditis in EIBS-affected coho salmon are caused by PRV-2 infection.
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Affiliation(s)
- Tomokazu Takano
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Satoshi Miwa
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Tomomasa Matsuyama
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Ikunari Kiryu
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Miho Honjo
- Miyagi Prefecture Fisheries Technology Institute, Ishinomaki, Japan
| | - Takamitsu Sakai
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Yuta Matsuura
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Masatoshi Yamasaki
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
| | - Akira Kumagai
- Miyagi Prefecture Fisheries Technology Institute, Ishinomaki, Japan
| | - Chihaya Nakayasu
- Pathology Division, Aquaculture Research Department, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Minami-ise, Japan
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3
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Solarte-Murillo L, Reyes H, Ojeda L, Cárcamo JG, Pontigo JP, Loncoman CA. Analyses and Insights into Genetic Reassortment and Natural Selection as Key Drivers of Piscine orthoreovirus Evolution. Viruses 2024; 16:556. [PMID: 38675898 PMCID: PMC11053957 DOI: 10.3390/v16040556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2024] [Revised: 03/05/2024] [Accepted: 03/08/2024] [Indexed: 04/28/2024] Open
Abstract
Piscine orthoreovirus (PRV) is a pathogen that causes heart and skeletal muscle inflammation in Salmo salar and has also been linked to circulatory disorders in other farmed salmonids, such as Oncorhynchus kisutch and Oncorhynchus mykiss. The virus has a segmented, double-stranded RNA genome, which makes it possible to undergo genetic reassortment and increase its genomic diversity through point mutations. In this study, genetic reassortment in PRV was assessed using the full genome sequences available in public databases. This study used full genome sequences that were concatenated and genome-wide reassortment events, and phylogenetic analyses were performed using the recombination/reassortment detection program version 5 (RDP5 V 5.5) software. Additionally, each segment was aligned codon by codon, and overall mean distance and selection was tested using the Molecular Evolutionary Genetics Analysis X software, version 10.2 (MEGA X version 10.2). The results showed that there were 17 significant reassortment events in 12 reassortant sequences, involving genome exchange between low and highly virulent genotypes. PRV sequences from different salmonid host species did not appear to limit the reassortment. This study found that PRV frequently undergoes reassortment events to increase the diversity of its segmented genome, leading to antigenic variation and increased virulence. This study also noted that to date, no reassortment events have been described between PRV-1 and PRV-3 genotypes. However, the number of complete genomic sequences within each genotype is uneven. This is important because PRV-3 induces cross-protection against PRV-1, making it a potential vaccine candidate.
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Affiliation(s)
- Laura Solarte-Murillo
- Laboratorio de Virología Molecular, Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia 5090000, Chile;
| | - Humberto Reyes
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago 8331150, Chile;
| | - Loreto Ojeda
- Laboratorio de Bioquímica Farmacológica, Virología y Biotecnología, Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia 5090000, Chile
- Interdisciplinary Center for Aquaculture Research, INCAR, Concepción 4030000, Chile
| | - Juan G. Cárcamo
- Laboratorio de Bioquímica Farmacológica, Virología y Biotecnología, Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia 5090000, Chile
- Interdisciplinary Center for Aquaculture Research, INCAR, Concepción 4030000, Chile
| | - Juan Pablo Pontigo
- Laboratorio Institucional, Facultad de Ciencias de la Naturaleza, Escuela de Medicina Veterinaria, Universidad San Sebastián, Puerto Montt 5400000, Chile;
| | - Carlos A. Loncoman
- Laboratorio de Virología Molecular, Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia 5090000, Chile;
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4
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Brimsholm M, Fjelldal PG, Hansen T, Fraser TKW, Solberg M, Glover K, Koppang EO, Bjørgen H. Red and melanized focal changes in white skeletal muscle in Atlantic salmon (Salmo salar): Comparative analysis of farmed, wild and hybrid fish reared under identical conditions. JOURNAL OF FISH DISEASES 2023; 46:1377-1389. [PMID: 37675872 DOI: 10.1111/jfd.13856] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 08/16/2023] [Accepted: 08/22/2023] [Indexed: 09/08/2023]
Abstract
Selective breeding plays a vital role in the production of farmed Atlantic salmon and has shown success in many aspects. Still, challenges related to fish health and welfare continue to result in significant economic losses. One such challenge is red and melanized focal changes (RFC/MFC), which result from acute and chronic inflammation, respectively, in the skeletal muscle. Importantly, RFC/MFC has not been observed in wild Atlantic salmon, suggesting that both external and genetic factors may contribute to the development of inflammation. To investigate the underlying cause of RFC/MFC, we conducted a study involving 1854 Atlantic salmon of farmed, wild and hybrid origin. All fish were reared under identical conditions to minimize the influence of external factors. Throughout the production cycle, the fish was monitored for growth parameters and examined for RFC/MFC using macroscopic and histological analysis. We found no association between the experimental groups and the presence of RFC/MFC. Histological investigations revealed melano-macrophages in the soft tissue in freshwater smolt, although no macroscopic discoloration was observed. MFC showed granulomas in various stages, suggesting a complex progression of the condition. In summary, we conclude that RFC/MFC is primarily caused by external factors found in the rearing facilities of farmed Atlantic salmon.
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Affiliation(s)
- Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | - Tom Hansen
- Matre Research Station, Institute of Marine Research, Matredal, Norway
| | | | - Monica Solberg
- Population Genetics Research Group, Institute of Marine Research, Bergen, Norway
| | - Kevin Glover
- Population Genetics Research Group, Institute of Marine Research, Bergen, Norway
| | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
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5
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Kannimuthu D, Roh H, Peñaranda MMD, Wessel Ø, Mæhle S, Berhe GD, Nordbø J, Kvamme BO, Morton HC, Grove S. Long-term persistence of piscine orthoreovirus-1 (PRV-1) infection during the pre-smolt stages of Atlantic salmon in freshwater. Vet Res 2023; 54:69. [PMID: 37644605 PMCID: PMC10463814 DOI: 10.1186/s13567-023-01201-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Accepted: 07/07/2023] [Indexed: 08/31/2023] Open
Abstract
Piscine orthoreovirus (PRV) causes heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon. During salmon production cycles, HSMI has predominantly been observed after seawater transfer. More recently, better surveillance and longitudinal studies have detected occurrences of PRV-1 in freshwater broodstock farms and hatcheries. However, very little is known about the viral kinetics of PRV-1 or disease development of HSMI during these pre-smolt stages. In this study, we conducted a long-term PRV-1 challenge experiment to examine the profile of viral load, infectiousness and/or clearance in Atlantic salmon during their development from fry to parr stage. Atlantic salmon fry (mean weight: 1.1 ± 0.19 g) were infected with PRV-1 (high virulent variant) via intraperitoneal (IP) injection. The viral load reached a peak at 2-4 weeks post-challenge (wpc) in heart and muscle tissues. The virus was detected at relatively high levels in whole blood, spleen, and head kidney tissues until 65 wpc. Heart and muscle lesions typical of HSMI were clearly observed at 6 and 8 wpc but then subsided afterwards resolving inflammation. Innate and adaptive immune responses were elicited during the early/acute phase but returned to basal levels during the persistent phase of infection. Despite achieving high viremia, PRV-1 infection failed to cause any mortality during the 65-week virus challenge period. Cohabitation of PRV-1 infected fish (10 and 31 wpc) with naïve Atlantic salmon fry resulted in very low or no infection. Moreover, repeated chasing stress exposures did not affect the viral load or shedding of PRV-1 at 26 and 44 wpc. The present findings provide knowledge about PRV-1 infection in juvenile salmon and highlight the importance of continued monitoring and management to prevent and mitigate the PRV-1 infection in freshwater facilities.
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Affiliation(s)
| | - HyeongJin Roh
- Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway
| | | | - Øystein Wessel
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433, Ås, Norway
| | - Stig Mæhle
- Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway
| | | | - Joachim Nordbø
- Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway
| | - Bjørn Olav Kvamme
- Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway
| | - H Craig Morton
- Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway
| | - Søren Grove
- Institute of Marine Research, Nordnes, P.O. Box 1870, N-5817, Bergen, Norway
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6
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Rennemo J, Myrvold S, Berge K, Kileng Ø, Pedersen B, Aksberg DS, Lisik P, Crappe D, McGurk C, Rimstad E, Wessel Ø, Koppang EO, Bjørgen H. In-depth health surveillance and clinical nutrition in farmed Atlantic salmon: a strategic attempt to detect and mitigate an HSMI outbreak. Vet Res 2023; 54:3. [PMID: 36694262 PMCID: PMC9872415 DOI: 10.1186/s13567-023-01137-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Accepted: 12/07/2022] [Indexed: 01/26/2023] Open
Abstract
Fish health personnel have limited tools in combatting viral diseases such as heart and skeletal muscle inflammation (HSMI) in open net-pen farmed Atlantic salmon. In this study, we aimed to predict HSMI by intensified health monitoring and apply clinical nutrition to mitigate the condition. We followed a commercial cohort (G1) of Atlantic salmon that was PRV-1 naïve when transferred to a sea cage at a location where HSMI outbreaks commonly occur. The fish in the other cages (G2-G6) at the location had a different origin than G1 and were PRV-1 positive prior to sea transfer. By continuous analysis of production data and sequentially (approximately every fourth week) performing autopsy, RT-qPCR (for PRV-1 and selected immune genes), blood and histological analysis of 10 fish from G1 and G2, we identified the time of PRV-1 infection in G1 and predicted the onset of HSMI prior to any clinical signs of disease. Identical sequences across partial genomes of PRV-1 isolates from G1 and G2 suggest the likely transfer from infected cages to G1. The isolates were grouped into a genogroup known to be of high virulence. A commercial health diet was applied during the HSMI outbreak, and the fish had low mortality and an unaffected appetite. In conclusion, we show that fish health and welfare can benefit from in-depth health monitoring. We also discuss the potential health value of clinical nutrition as a mean to mitigate HSMI.
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Affiliation(s)
- Johan Rennemo
- grid.436785.b0000 0004 0644 9116Skretting AS, Stavanger, Norway
| | | | - Kjetil Berge
- grid.436785.b0000 0004 0644 9116Skretting AS, Stavanger, Norway
| | | | - Børge Pedersen
- grid.436785.b0000 0004 0644 9116Skretting AS, Stavanger, Norway
| | | | - Piotr Lisik
- Skretting Aquaculture Innovation (AI), Stavanger, Norway
| | | | - Charles McGurk
- Skretting Aquaculture Innovation (AI), Stavanger, Norway
| | - Espen Rimstad
- grid.19477.3c0000 0004 0607 975XUnit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Øystein Wessel
- grid.19477.3c0000 0004 0607 975XUnit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Erling Olaf Koppang
- grid.19477.3c0000 0004 0607 975XUnit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Håvard Bjørgen
- grid.19477.3c0000 0004 0607 975XUnit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
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7
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Sánchez-Roncancio C, García B, Gallardo-Hidalgo J, Yáñez JM. GWAS on Imputed Whole-Genome Sequence Variants Reveal Genes Associated with Resistance to Piscirickettsia salmonis in Rainbow Trout ( Oncorhynchus mykiss). Genes (Basel) 2022; 14:114. [PMID: 36672855 PMCID: PMC9859203 DOI: 10.3390/genes14010114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 12/27/2022] [Accepted: 12/28/2022] [Indexed: 12/31/2022] Open
Abstract
Genome-wide association studies (GWAS) allow the identification of associations between genetic variants and important phenotypes in domestic animals, including disease-resistance traits. Whole Genome Sequencing (WGS) data can help increase the resolution and statistical power of association mapping. Here, we conduced GWAS to asses he facultative intracellular bacterium Piscirickettsia salmonis, which affects farmed rainbow trout, Oncorhynchus mykiss, in Chile using imputed genotypes at the sequence level and searched for candidate genes located in genomic regions associated with the trait. A total of 2130 rainbow trout were intraperitoneally challenged with P. salmonis under controlled conditions and genotyped using a 57K single nucleotide polymorphism (SNP) panel. Genotype imputation was performed in all the genotyped animals using WGS data from 102 individuals. A total of 488,979 imputed WGS variants were available in the 2130 individuals after quality control. GWAS revealed genome-wide significant quantitative trait loci (QTL) in Omy02, Omy03, Omy25, Omy26 and Omy27 for time to death and in Omy26 for binary survival. Twenty-four (24) candidate genes associated with P. salmonis resistance were identified, which were mainly related to phagocytosis, innate immune response, inflammation, oxidative response, lipid metabolism and apoptotic process. Our results provide further knowledge on the genetic variants and genes associated with resistance to intracellular bacterial infection in rainbow trout.
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Affiliation(s)
- Charles Sánchez-Roncancio
- Doctorado en Acuicultura, Programa Cooperativo: Universidad de Chile. Universidad Católica del Norte. Pontificia Universidad Católica de Valparaíso, Chile
- Center for Research and Innovation in Aquaculture (CRIA), Universidad de Chile, Santiago 8820808, Chile
| | - Baltasar García
- Center for Research and Innovation in Aquaculture (CRIA), Universidad de Chile, Santiago 8820808, Chile
- Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, La Pintana, Santiago 8820808, Chile
| | - Jousepth Gallardo-Hidalgo
- Center for Research and Innovation in Aquaculture (CRIA), Universidad de Chile, Santiago 8820808, Chile
- Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, La Pintana, Santiago 8820808, Chile
| | - José M. Yáñez
- Center for Research and Innovation in Aquaculture (CRIA), Universidad de Chile, Santiago 8820808, Chile
- Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, La Pintana, Santiago 8820808, Chile
- Núcleo Milenio de Salmonidos Invasores Australes (INVASAL), Concepcion 4030000, Chile
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8
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Vallejos-Vidal E, Reyes-López FE, Sandino AM, Imarai M. Sleeping With the Enemy? The Current Knowledge of Piscine Orthoreovirus (PRV) Immune Response Elicited to Counteract Infection. Front Immunol 2022; 13:768621. [PMID: 35464421 PMCID: PMC9019227 DOI: 10.3389/fimmu.2022.768621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 02/25/2022] [Indexed: 11/13/2022] Open
Abstract
Piscine orthoreovirus (PRV) is a virus in the genus Orthoreovirus of the Reoviridae family, first described in 2010 associated with Heart and Skeletal Muscle Inflammation (HSMI) in Atlantic salmon (Salmo salar). Three phases of PRV infection have been described, the early entry and dissemination, the acute dissemination phase, and the persistence phase. Depending on the PRV genotype and the host, infection can last for life. Mechanisms of immune response to PRV infection have been just beginning to be studied and the knowledge in this matter is here revised. PRV induces a classical antiviral immune response in experimental infection of salmonid erythrocytes, including transcriptional upregulation of ifn-α, rig-i, mx, and pkr. In addition, transcript upregulation of tcra, tcrb, cd2, il-2, cd4-1, ifn-γ, il-12, and il-18 has been observed in Atlantic salmon infected with PRV, indicating that PRV elicited a Th1 type response probably as a host defense strategy. The high expression levels of cd8a, cd8b, and granzyme-A in PRV-infected fish suggest a positive modulatory effect on the CTL-mediated immune response. This is consistent with PRV-dependent upregulation of the genes involved in antigen presentation, including MHC class I, transporters, and proteasome components. We also review the potential immune mechanisms associated with the persistence phenotype of PRV-infected fish and its consequence for the development of a secondary infection. In this scenario, the application of a vaccination strategy is an urgent and challenging task due to the emergence of this viral infection that threatens salmon farming.
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Affiliation(s)
- Eva Vallejos-Vidal
- Centro de Biotecnología Acuícola, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.,Facultad de Medicina Veterinaria y Agronomía, Universidad de Las Américas, Santiago, Chile
| | - Felipe E Reyes-López
- Centro de Biotecnología Acuícola, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.,Department of Cell Biology, Physiology, and Immunology, Universitat Autònoma de Barcelona, Barcelona, Spain
| | - Ana María Sandino
- Centro de Biotecnología Acuícola, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.,Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Mónica Imarai
- Centro de Biotecnología Acuícola, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.,Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
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9
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Malik MS, Nyman IB, Wessel Ø, Dahle MK, Rimstad E. Dynamics of Polarized Macrophages and Activated CD8 + Cells in Heart Tissue of Atlantic Salmon Infected With Piscine Orthoreovirus-1. Front Immunol 2021; 12:729017. [PMID: 34603301 PMCID: PMC8481380 DOI: 10.3389/fimmu.2021.729017] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 08/31/2021] [Indexed: 11/13/2022] Open
Abstract
Piscine orthoreovirus (PRV-1) infection causes heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar). The virus is also associated with focal melanized changes in white skeletal muscle where PRV-1 infection of macrophages appears to be important. In this study, we studied the macrophage polarization into M1 (pro-inflammatory) and M2 (anti-inflammatory) phenotypes during experimentally induced HSMI. The immune response in heart with HSMI lesions was characterized by CD8+ and MHC-I expressing cells and not by polarized macrophages. Fluorescent in situ hybridization (FISH) assays revealed localization of PRV-1 in a few M1 macrophages in both heart and skeletal muscle. M2 type macrophages were widely scattered in the heart and were more abundant in heart compared to the skeletal muscle. However, the M2 macrophages did not co-stain for PRV-1. There was a strong cellular immune response to the infection in the heart compared to that of the skeletal muscle, seen as increased MHC-I expression, partly in cells also containing PRV-1 RNA, and a high number of cytotoxic CD8+ granzyme producing cells that targeted PRV-1. In skeletal muscle, MHC-I expressing cells and CD8+ cells were dispersed between myocytes, but these cells did not stain for PRV-1. Gene expression analysis by RT-qPCR complied with the FISH results and confirmed a drop in level of PRV-1 following the cell mediated immune response. Overall, the results indicated that M1 macrophages do not contribute to the initial development of HSMI. However, large numbers of M2 macrophages reside in the heart and may contribute to the subsequent fast recovery following clearance of PRV-1 infection.
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Affiliation(s)
- Muhammad Salman Malik
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Ingvild Berg Nyman
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Øystein Wessel
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Maria K Dahle
- Department of Fish Health, Norwegian Veterinary Institute, Ås, Norway
| | - Espen Rimstad
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
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10
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Piscine Orthoreovirus (PRV)-3, but Not PRV-2, Cross-Protects against PRV-1 and Heart and Skeletal Muscle Inflammation in Atlantic Salmon. Vaccines (Basel) 2021; 9:vaccines9030230. [PMID: 33800725 PMCID: PMC8001985 DOI: 10.3390/vaccines9030230] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 02/26/2021] [Accepted: 03/02/2021] [Indexed: 02/06/2023] Open
Abstract
Heart and skeletal muscle inflammation (HSMI), caused by infection with Piscine orthoreovirus-1 (PRV-1), is a common disease in farmed Atlantic salmon (Salmo salar). Both an inactivated whole virus vaccine and a DNA vaccine have previously been tested experimentally against HSMI and demonstrated to give partial but not full protection. To understand the mechanisms involved in protection against HSMI and evaluate the potential of live attenuated vaccine strategies, we set up a cross-protection experiment using PRV genotypes not associated with disease development in Atlantic salmon. The three known genotypes of PRV differ in their preference of salmonid host species. The main target species for PRV-1 is Atlantic salmon. Coho salmon (Oncorhynchus kisutch) is the target species for PRV-2, where the infection may induce erythrocytic inclusion body syndrome (EIBS). PRV-3 is associated with heart pathology and anemia in rainbow trout, but brown trout (S. trutta) is the likely natural main host species. Here, we tested if primary infection with PRV-2 or PRV-3 in Atlantic salmon could induce protection against secondary PRV-1 infection, in comparison with an adjuvanted, inactivated PRV-1 vaccine. Viral kinetics, production of cross-reactive antibodies, and protection against HSMI were studied. PRV-3, and to a low extent PRV-2, induced antibodies cross-reacting with the PRV-1 σ1 protein, whereas no specific antibodies were detected after vaccination with inactivated PRV-1. Ten weeks after immunization, the fish were challenged through cohabitation with PRV-1-infected shedder fish. A primary PRV-3 infection completely blocked PRV-1 infection, while PRV-2 only reduced PRV-1 infection levels and the severity of HSMI pathology in a few individuals. This study indicates that infection with non-pathogenic, replicating PRV could be a future strategy to protect farmed salmon from HSMI.
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Malik MS, Bjørgen H, Nyman IB, Wessel Ø, Koppang EO, Dahle MK, Rimstad E. PRV-1 Infected Macrophages in Melanized Focal Changes in White Muscle of Atlantic Salmon ( Salmo salar) Correlates With a Pro-Inflammatory Environment. Front Immunol 2021; 12:664624. [PMID: 33995395 PMCID: PMC8116804 DOI: 10.3389/fimmu.2021.664624] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 04/13/2021] [Indexed: 12/27/2022] Open
Abstract
Melanized focal changes in white skeletal muscle of farmed Atlantic salmon, "black spots", is a quality problem affecting on average 20% of slaughtered fish. The spots appear initially as "red spots" characterized by hemorrhages and acute inflammation and progress into black spots characterized by chronic inflammation and abundant pigmented cells. Piscine orthoreovirus 1 (PRV-1) was previously found to be associated with macrophages and melano-macrophages in red and black spots. Here we have addressed the inflammatory microenvironment of red and black spots by studying the polarization status of the macrophages and cell mediated immune responses in spots, in both PRV-1 infected and non-infected fish. Samples that had been collected at regular intervals through the seawater production phase in a commercial farm were analyzed by multiplex fluorescent in situ hybridization (FISH) and RT-qPCR methods. Detection of abundant inducible nitric oxide synthase (iNOS2) expressing M1-polarized macrophages in red spots demonstrated a pro-inflammatory microenvironment. There was an almost perfect co-localization with the iNOS2 expression and PRV-1 infection. Black spots, on the other side, had few iNOS2 expressing cells, but a relatively high number of arginase-2 expressing anti-inflammatory M2-polarized macrophages containing melanin. The numerous M2-polarized melano-macrophages in black spots indicate an ongoing healing phase. Co-localization of PRV-1 and cells expressing CD8+ and MHC-I suggests a targeted immune response taking place in the spots. Altogether, this study indicates that PRV-1 induces a pro-inflammatory environment that is important for the pathogenesis of the spots. We do not have indication that infection of PRV-1 is the initial causative agent of this condition.
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Affiliation(s)
- Muhammad Salman Malik
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Håvard Bjørgen
- Section of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Ingvild Berg Nyman
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Øystein Wessel
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Erling Olaf Koppang
- Section of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Maria K. Dahle
- Department of Fish Health, Norwegian Veterinary Institute, Oslo, Norway
| | - Espen Rimstad
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
- *Correspondence: Espen Rimstad,
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12
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Piscine Orthoreovirus-1 Isolates Differ in Their Ability to Induce Heart and Skeletal Muscle Inflammation in Atlantic Salmon ( Salmo salar). Pathogens 2020; 9:pathogens9121050. [PMID: 33327651 PMCID: PMC7765100 DOI: 10.3390/pathogens9121050] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Revised: 12/10/2020] [Accepted: 12/11/2020] [Indexed: 12/13/2022] Open
Abstract
Piscine orthoreovirus 1 (PRV-1) is the causative agent of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar). The virus is widespread in Atlantic salmon and was present in Norway long before the first description of HSMI in 1999. Furthermore, in Canada the virus is prevalent in farmed Atlantic salmon but HSMI is not and Canadian isolates have failed to reproduce HSMI experimentally. This has led to the hypothesis that there are virulence differences between PRV-1 isolates. In this study we performed a dose standardized challenge trial, comparing six PRV-1 isolates, including two Norwegian field isolates from 2018, three historical Norwegian isolates predating the first report of HSMI and one Canadian isolate. The Norwegian 2018 isolates induced lower viral protein load in blood cells but higher plasma viremia. Following peak replication in blood, the two Norwegian 2018 isolates induced histopathological lesions in the heart consistent with HSMI, whereas all three historical Norwegian and the Canadian isolates induced only mild cardiac lesions. This is the first demonstration of virulence differences between PRV-1 isolates and the phenotypic differences are linked to viral proteins encoded by segment S1, M2, L1, L2 and S4.
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13
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Polinski MP, Vendramin N, Cuenca A, Garver KA. Piscine orthoreovirus: Biology and distribution in farmed and wild fish. JOURNAL OF FISH DISEASES 2020; 43:1331-1352. [PMID: 32935367 DOI: 10.1111/jfd.13228] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 07/06/2020] [Accepted: 07/08/2020] [Indexed: 06/11/2023]
Abstract
Piscine orthoreovirus (PRV) is a common and widely distributed virus of salmonids. Since its discovery in 2010, the virus has been detected in wild and farmed stocks from North America, South America, Europe and East Asia in both fresh and salt water environments. Phylogenetic analysis suggests three distinct genogroups of PRV with generally discrete host tropisms and/or regional patterns. PRV-1 is found mainly in Atlantic (Salmo salar), Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) Salmon of Europe and the Americas; PRV-2 has only been detected in Coho Salmon of Japan; and PRV-3 has been reported primarily in Rainbow Trout (Oncorhynchus mykiss) in Europe. All three genotypes can establish high-load systemic infections by targeting red blood cells for principal replication. Each genotype has also demonstrated potential to cause circulatory disease. At the same time, high-load PRV infections occur in non-diseased salmon and trout, indicating a complexity for defining PRV's role in disease aetiology. Here, we summarize the current body of knowledge regarding PRV following 10 years of study.
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Affiliation(s)
- Mark P Polinski
- Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, BC, Canada
| | - Niccoló Vendramin
- National Institute of Aquatic Resources, Technical University of Denmark, Lyngby, Denmark
| | - Argelia Cuenca
- National Institute of Aquatic Resources, Technical University of Denmark, Lyngby, Denmark
| | - Kyle A Garver
- Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, BC, Canada
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Pham PH, Misk E, Papazotos F, Jones G, Polinski MP, Contador E, Russell S, Garver KA, Lumsden JS, Bols NC. Screening of Fish Cell Lines for Piscine Orthoreovirus-1 (PRV-1) Amplification: Identification of the Non-Supportive PRV-1 Invitrome. Pathogens 2020; 9:E833. [PMID: 33053677 PMCID: PMC7601784 DOI: 10.3390/pathogens9100833] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 10/05/2020] [Accepted: 10/09/2020] [Indexed: 12/16/2022] Open
Abstract
Piscine reovirus (PRV) is the causative agent of heart and skeletal muscle inflammation (HSMI), which is detrimental to Atlantic Salmon (AS) aquaculture, but so far has not been cultivatable, which impedes studying the disease and developing a vaccine. Homogenates of head kidney and red blood cells (RBC) from AS in which PRV-1 had been detected were applied to fish cell lines. The cell lines were from embryos, and from brain, blood, fin, gill, gonads, gut, heart, kidney, liver, skin, and spleen, and had the shapes of endothelial, epithelial, fibroblast, and macrophage cells. Most cell lines were derived from the Neopterygii subclass of fish, but one was from subclass Chondrostei. Cultures were examined by phase contrast microscopy for appearance, and by quantitative polymerase chain reaction (qPCR) for PRV-1 RNA amplification and for the capacity to transfer any changes to new cultures. No changes in appearance and Ct values were observed consistently or transferable to new cultures. Therefore, 31 cell lines examined were unable to support PRV-1 amplification and are described as belonging to the non-supportive PRV-1 invitrome. However, these investigations and cell lines can contribute to understanding PRV-1 cellular and host tropism, and the interactions between virus-infected and bystander cells.
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Affiliation(s)
- Phuc H. Pham
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada; (F.P.); (N.C.B.)
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada; (E.C.); (J.S.L.)
| | - Ehab Misk
- Huntsman Marine Science Centre, St. Andrews, NB E5B 2L7, Canada;
| | - Fotini Papazotos
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada; (F.P.); (N.C.B.)
| | - Ginny Jones
- Elanco Canada Limited, Aqua Vaccines R&D, Charlottetown, PE C1E 2A7, Canada;
| | - Mark P. Polinski
- Pacific Biological Station, Department of Fisheries and Oceans, Nanaimo, BC V9T 6N7, Canada; (M.P.P.); (K.A.G.)
| | - Elena Contador
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada; (E.C.); (J.S.L.)
| | - Spencer Russell
- Fisheries and Aquaculture, Vancouver Island University, Nanaimo, BC V9R 5S5, Canada;
| | - Kyle A. Garver
- Pacific Biological Station, Department of Fisheries and Oceans, Nanaimo, BC V9T 6N7, Canada; (M.P.P.); (K.A.G.)
| | - John S. Lumsden
- Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada; (E.C.); (J.S.L.)
| | - Niels C. Bols
- Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada; (F.P.); (N.C.B.)
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Bakke AF, Bjørgen H, Koppang EO, Frost P, Afanasyev S, Boysen P, Krasnov A, Lund H. IgM+ and IgT+ B Cell Traffic to the Heart during SAV Infection in Atlantic Salmon. Vaccines (Basel) 2020; 8:E493. [PMID: 32878234 PMCID: PMC7563723 DOI: 10.3390/vaccines8030493] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 08/24/2020] [Accepted: 08/24/2020] [Indexed: 02/02/2023] Open
Abstract
B cells of teleost fish differentiate in the head kidney, and spleen, and either remain in the lymphatic organs or move to the blood and peripheral tissues. There is limited knowledge about piscine B cell traffic to sites of vaccination and infection and their functional roles at these sites. In this work, we examined the traffic of B cells in Atlantic salmon challenged with salmonid alphavirus (SAV). In situ hybridization (RNAScope) showed increased numbers of immunoglobin (Ig)M+ and IgT+ B cells in the heart in response to SAV challenge, with IgM+ B cells being most abundant. An increase in IgT+ B cells was also evident, indicating a role of IgT+ B cells in nonmucosal tissues and systemic viral infections. After infection, B cells were mainly found in the stratum spongiosum of the cardiac ventricle, colocalizing with virus-infected myocardial-like cells. From sequencing the variable region of IgM in the main target organ (heart) and comparing it with a major lymphatic organ (the spleen), co-occurrence in antibody repertoires indicated a transfer of B cells from the spleen to the heart, as well as earlier recruitment of B cells to the heart in vaccinated fish compared to those that were unvaccinated. Transcriptome analyses performed at 21 days post-challenge suggested higher expression of multiple mediators of inflammation and lymphocyte-specific genes in unvaccinated compared to vaccinated fish, in parallel with a massive suppression of genes involved in heart contraction, metabolism, and development of tissue. The adaptive responses to SAV in vaccinated salmon appeared to alleviate the disease. Altogether, these results suggest that migration of B cells from lymphatic organs to sites of infection is an important part of the adaptive immune response of Atlantic salmon to SAV.
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Affiliation(s)
- Anne Flore Bakke
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ullevålsveien 72, 0454 Oslo, Norway; (A.F.B.); (H.B.); (E.O.K.); (P.B.); (H.L.)
| | - Håvard Bjørgen
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ullevålsveien 72, 0454 Oslo, Norway; (A.F.B.); (H.B.); (E.O.K.); (P.B.); (H.L.)
| | - Erling Olaf Koppang
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ullevålsveien 72, 0454 Oslo, Norway; (A.F.B.); (H.B.); (E.O.K.); (P.B.); (H.L.)
| | - Petter Frost
- MSD Animal Health Innovation AD, Thormøhlens Gate 55, 5006 Bergen, Norway;
| | - Sergey Afanasyev
- I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Torez 44, Saint-Petersburg 194223, Russia;
| | - Preben Boysen
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ullevålsveien 72, 0454 Oslo, Norway; (A.F.B.); (H.B.); (E.O.K.); (P.B.); (H.L.)
| | | | - Hege Lund
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ullevålsveien 72, 0454 Oslo, Norway; (A.F.B.); (H.B.); (E.O.K.); (P.B.); (H.L.)
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16
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Purcell MK, Powers RL, Taksdal T, McKenney D, Conway CM, Elliott DG, Polinski M, Garver K, Winton J. Consequences of Piscine orthoreovirus genotype 1 (PRV-1) infections in Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch) and rainbow trout (O. mykiss). JOURNAL OF FISH DISEASES 2020; 43:719-728. [PMID: 32476167 PMCID: PMC7384080 DOI: 10.1111/jfd.13182] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 02/03/2020] [Accepted: 02/05/2020] [Indexed: 05/02/2023]
Abstract
Piscine orthoreovirus genotype 1 (PRV-1) is the causative agent of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar L.). The virus has also been found in Pacific salmonids in western North America, raising concerns about the risk to native salmon and trout. Here, we report the results of laboratory challenges using juvenile Chinook salmon, coho salmon and rainbow trout injected with tissue homogenates from Atlantic salmon testing positive for PRV-1 or with control material. Fish were sampled at intervals to assess viral RNA transcript levels, haematocrit, erythrocytic inclusions and histopathology. While PRV-1 replicated in all species, there was negligible mortality in any group. We observed a few erythrocytic inclusion bodies in fish from the PRV-1-infected groups. At a few time points, haematocrits were significantly lower in the PRV-1-infected groups relative to controls, but in no case was anaemia noted. The most common histopathological finding was mild, focal myocarditis in both the non-infected controls and PRV-1-infected fish. All cardiac lesions were judged mild, and none were consistent with those of HSMI. Together, these results suggest all three species are susceptible to PRV-1 infection, but in no case did infection cause notable disease in these experiments.
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Affiliation(s)
| | - Rachel L. Powers
- U.S. Geological SurveyWestern Fisheries Research CenterSeattleWAUSA
| | | | - Doug McKenney
- School of Aquatic and Fishery SciencesUniversity of WashingtonSeattleWAUSA
| | - Carla M. Conway
- U.S. Geological SurveyWestern Fisheries Research CenterSeattleWAUSA
| | - Diane G. Elliott
- U.S. Geological SurveyWestern Fisheries Research CenterSeattleWAUSA
| | - Mark Polinski
- Pacific Biological Station, Fisheries and Oceans CanadaNanaimoBCCanada
| | - Kyle Garver
- Pacific Biological Station, Fisheries and Oceans CanadaNanaimoBCCanada
| | - James Winton
- U.S. Geological SurveyWestern Fisheries Research CenterSeattleWAUSA
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Dissemination of Piscine orthoreovirus-1 (PRV-1) in Atlantic Salmon ( Salmo salar) during the Early and Regenerating Phases of Infection. Pathogens 2020; 9:pathogens9020143. [PMID: 32093243 PMCID: PMC7169402 DOI: 10.3390/pathogens9020143] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 02/14/2020] [Accepted: 02/17/2020] [Indexed: 12/12/2022] Open
Abstract
Piscine orthoreovirus-1 (PRV-1) can cause heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar), but the line of events from infection, pathologic change, and regeneration has not been thoroughly described. In this study, the cellular localization and variation of PRV-1 RNA and protein levels were analyzed at different times post-exposure in experimentally infected Atlantic salmon. Immunohistochemistry, flow cytometry, and Western blot were used for assessment of the presence of the PRV-1 σ1 protein, while RT-qPCR and in situ hybridization were performed for viral RNA. Histopathologic evaluation demonstrated that PRV-1 infection induced heart lesions typical of HSMI, such as severe epicarditis and myocarditis with degeneration of cardiomyocytes, necrosis, and diffuse cellular infiltration. PRV-1 infection of erythrocytes and the peak viral plasma level preceded virus presence in cardiomyocytes and hepatocytes. Arginase-2-positive, macrophage-like cells observed in the heart indicated possible polarization to M2 macrophages and the onset of regenerative processes, which may contribute to the recovery from HSMI. The virus was cleared from regenerating heart tissue and from hepatocytes, but persisted in erythrocytes.
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