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Noguera P, Klinger M, Örün H, Grunow B, Del-Pozo J. Ultrastructural insights into the replication cycle of salmon pancreas disease virus (SPDV) using salmon cardiac primary cultures (SCPCs). JOURNAL OF FISH DISEASES 2021; 44:2031-2041. [PMID: 34424537 DOI: 10.1111/jfd.13518] [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: 05/13/2021] [Revised: 08/12/2021] [Accepted: 08/13/2021] [Indexed: 06/13/2023]
Abstract
Salmon pancreas disease virus (SPDV) has been affecting the salmon farming industry for over 30 years, but despite the substantial amount of studies, there are still a number of recognized knowledge gaps, for example in the transmission of the virus. In this work, an ultrastructural morphological approach was used to describe observations after infection by SPDV of an ex vivo cardiac model generated from Atlantic salmon embryos. The observations in this study and those available on previous ultrastructural work on SPDV are compared and contrasted with the current knowledge on terrestrial mammalian and insect alphaviral replication cycles, which is deeper than that of SPDV both morphologically and mechanistically. Despite their limitations, morphological descriptions remain an excellent way to generate novel hypotheses, and this has been the aim of this work. This study has used a target host, ex vivo model and resulted in some previously undescribed features, including filopodial membrane projections, cytoplasmic stress granules or putative intracytoplasmic budding. The latter suggests a new hypothesis that warrants further mechanistic research: SPDV in salmon may have retained the capacity for non-cytolytic (persistent) infections by intracellular budding, similar to that noted in arthropod vectors of other alphaviruses. In the notable absence of a known intermediate host for SPDV, the presence of this pattern suggests that both cytopathic and persistent infections may coexist in the same host. It is our hope that the ultrastructural comparison presented here stimulates new research that brings the knowledge on SPDV replication cycle up to a similar level to that of terrestrial alphaviruses.
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Affiliation(s)
| | | | - Histro Örün
- Institute of Anatomy, University of Lübeck, Lübeck, Germany
| | - Bianka Grunow
- Leibniz-Institute for Farm Animal Biology (FBN), Dummerstorf, Germany
| | - Jorge Del-Pozo
- Royal Dick School of Veterinary Sciences, University of Edinburgh, Roslin, UK
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2
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Emergence of Salmonid Alphavirus Genotype 2 in Norway-Molecular Characterization of Viral Strains Circulating in Norway and Scotland. Viruses 2021; 13:v13081556. [PMID: 34452421 PMCID: PMC8402823 DOI: 10.3390/v13081556] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Revised: 07/27/2021] [Accepted: 07/29/2021] [Indexed: 12/30/2022] Open
Abstract
Pancreas disease (PD) and sleeping disease (SD), caused by an alphavirus, are endemic in European salmonid aquaculture, causing significant mortality, reduced growth and poor flesh quality. In 2010, a new variant of salmonid alphavirus emerged in Norway, marine salmonid alphavirus genotype 2 (SAV2). As this genotype is highly prevalent in Scotland, transmission through well boat traffic was hypothesized as one possible source of infection. In this study, we performed full-length genome sequencing of SAV2 sampled between 2006 and 2012 in Norway and Scotland, and present the first comprehensive full-length characterization of Norwegian marine SAV2 strains. We analyze their relationship with selected Scottish SAV2 strains and explore the genetic diversity of SAV. Our results show that all Norwegian marine SAV2 share a recent last common ancestor with marine SAV2 circulating in Scotland and a higher level of genomic diversity among the Scottish marine SAV2 strains compared to strains from Norway. These findings support the hypothesis of a single introduction of SAV2 to Norway sometime from 2006-2010, followed by horizontal spread along the coast.
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3
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Teige LH, Aksnes I, Røsæg MV, Jensen I, Jørgensen J, Sindre H, Collins C, Collet B, Rimstad E, Dahle MK, Boysen P. Detection of specific Atlantic salmon antibodies against salmonid alphavirus using a bead-based immunoassay. FISH & SHELLFISH IMMUNOLOGY 2020; 106:374-383. [PMID: 32738513 DOI: 10.1016/j.fsi.2020.07.055] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 07/20/2020] [Accepted: 07/24/2020] [Indexed: 06/11/2023]
Abstract
Salmonid alphavirus (SAV) is the etiological cause of pancreas disease (PD) in Atlantic salmon (Salmo salar). Several vaccines against SAV are in use, but PD still cause significant mortality and concern in European aquaculture, raising the need for optimal tools to monitor SAV immunity. To monitor and control the distribution of PD in Norway, all salmonid farms are regularly screened for SAV by RT-qPCR. While the direct detection of SAV is helpful in the early stages of infection, serological methods could bring additional information on acquired SAV immunity in the later stages. Traditionally, SAV antibodies are monitored in neutralization assays, but they are time-consuming and cumbersome, thus alternative assays are warranted. Enzyme-linked immunosorbent assays (ELISAs) have not yet been successfully used for anti-SAV antibody detection in aquaculture. We aimed to develop a bead-based immunoassay for SAV-specific antibodies. By using detergent-treated SAV particles as antigens, we detected SAV-specific antibodies in plasma collected from both a SAV challenge trial and a field outbreak of PD. Increased levels of SAV-specific antibodies were seen after most fish had become negative for viral RNA. The bead-based assay is time saving compared to virus neutralization assays, and suitable for non-lethal testing due to low sample size requirements. We conclude that the bead-based immunoassay for SAV antibody detection is a promising diagnostic tool to complement SAV screening in aquaculture.
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Affiliation(s)
- Lena Hammerlund Teige
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Oslo, Norway
| | - Ida Aksnes
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Oslo, Norway
| | | | - Ingvill Jensen
- The Norwegian College of Fishery Science, UiT The Arctic University of Norway, Tromsø, Norway
| | - Jorunn Jørgensen
- The Norwegian College of Fishery Science, UiT The Arctic University of Norway, Tromsø, Norway
| | - Hilde Sindre
- Department of Fish Health, Norwegian Veterinary Institute, Oslo, Norway
| | - Catherine Collins
- Université Paris-Saclay, INRAE, UVSQ, VIM, 78350, Jouy-en-Josas, France
| | - Bertrand Collet
- Université Paris-Saclay, INRAE, UVSQ, VIM, 78350, Jouy-en-Josas, France
| | - Espen Rimstad
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Oslo, Norway
| | - Maria K Dahle
- The Norwegian College of Fishery Science, UiT The Arctic University of Norway, Tromsø, Norway; Department of Fish Health, Norwegian Veterinary Institute, Oslo, Norway
| | - Preben Boysen
- Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Oslo, Norway.
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4
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Aksnes I, Markussen T, Braaen S, Rimstad E. Mutation of N-glycosylation Sites in Salmonid Alphavirus (SAV) Envelope Proteins Attenuate the Virus in Cell Culture. Viruses 2020; 12:v12101071. [PMID: 32987930 PMCID: PMC7650630 DOI: 10.3390/v12101071] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 09/18/2020] [Accepted: 09/21/2020] [Indexed: 12/16/2022] Open
Abstract
Salmonid alphavirus (SAV) is the cause of pancreas disease and sleeping disease in farmed salmonid fish in Europe. The spread of these diseases has been difficult to control with biosecurity and current vaccination strategies, and increased understanding of the viral pathogenesis could be beneficial for the development of novel vaccine strategies. N-glycosylation of viral envelope proteins may be crucial for viral virulence and a possible target for its purposed attenuation. In this study, we mutated the N-glycosylation consensus motifs of the E1 and E2 glycoproteins of a SAV3 infectious clone using site-directed mutagenesis. Mutation of the glycosylation motif in E1 gave a complete inactivation of the virus as no viral replication could be detected in cell culture and infectious particles could not be rescued. In contrast, infectious virus particles could be recovered from the SAV3 E2 mutants (E2319Q, E2319A), but not if they were accompanied by lack of N-glycosylation in E1. Compared to the non-mutated infectious clone, the SAV3-E2319Q and SAV3-E2319A recombinant viruses produced less cytopathic effects in cell culture and lower amounts of infectious viral particles. In conclusion, the substitution in the N-linked glycosylation site in E2 attenuated SAV3 in cell culture. The findings could be useful for immunization strategies using live attenuated vaccines and testing in fish will be desirable to study the clone’s properties in vivo.
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5
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Hillestad B, Makvandi-Nejad S, Krasnov A, Moghadam HK. Identification of genetic loci associated with higher resistance to pancreas disease (PD) in Atlantic salmon (Salmo salar L.). BMC Genomics 2020; 21:388. [PMID: 32493246 PMCID: PMC7268189 DOI: 10.1186/s12864-020-06788-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2019] [Accepted: 05/20/2020] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND Pancreas disease (PD) is a contagious disease caused by salmonid alphavirus (SAV) with significant economic and welfare impacts on salmon farming. Previous work has shown that higher resistance against PD has underlying additive genetic components and can potentially be improved through selective breeding. To better understand the genetic basis of PD resistance in Atlantic salmon, we challenged 4506 smolts from 296 families of the SalmoBreed strain. Fish were challenged through intraperitoneal injection with the most virulent form of the virus found in Norway (i.e., SAV3). Mortalities were recorded, and more than 900 fish were further genotyped on a 55 K SNP array. RESULTS The estimated heritability for PD resistance was 0.41 ± 0.017. The genetic markers on two chromosomes, ssa03 and ssa07, showed significant associations with higher disease resistance. Collectively, markers on these two QTL regions explained about 60% of the additive genetic variance. We also sequenced and compared the cardiac transcriptomics of moribund fish and animals that survived the challenge with a focus on candidate genes within the chromosomal segments harbouring QTL. Approximately 200 genes, within the QTL regions, were found to be differentially expressed. Of particular interest, we identified various components of immunoglobulin-heavy-chain locus B (IGH-B) on ssa03 and immunoglobulin-light-chain on ssa07 with markedly higher levels of transcription in the resistant animals. These genes are closely linked to the most strongly QTL associated SNPs, making them likely candidates for further investigation. CONCLUSIONS The findings presented here provide supporting evidence that breeding is an efficient tool for increasing PD resistance in Atlantic salmon populations. The estimated heritability is one of the largest reported for any disease resistance in this species, where the majority of the genetic variation is explained by two major QTL. The transcriptomic analysis has revealed the activation of essential components of the innate and the adaptive immune responses following infection with SAV3. Furthermore, the complementation of the genomic with the transcriptomic data has highlighted the possible critical role of the immunoglobulin loci in combating PD virus.
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Affiliation(s)
| | | | - Aleksei Krasnov
- Division of Aquaculture, Norwegian Institute of Fisheries and Aquaculture (Nofima), P.O. Box 6122, Muninbakken 9-13, Breivika, Langnes, N-9291, Tromsø, Norway
| | - Hooman K Moghadam
- Benchmark Genetics Norway AS, Sandviksboder 3A, N-5035, Bergen, Norway.
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6
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Gallagher MD, Karlsen M, Petterson E, Haugland Ø, Matejusova I, Macqueen DJ. Genome Sequencing of SAV3 Reveals Repeated Seeding Events of Viral Strains in Norwegian Aquaculture. Front Microbiol 2020; 11:740. [PMID: 32390982 PMCID: PMC7193772 DOI: 10.3389/fmicb.2020.00740] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 03/30/2020] [Indexed: 01/14/2023] Open
Abstract
Understanding the dynamics of pathogen transfer in aquaculture systems is essential to manage and mitigate disease outbreaks. The goal of this study was to understand recent transmission dynamics of salmonid alphavirus (SAV) in Norway. SAV causes significant economic impacts on farmed salmonids in European aquaculture. SAV is classified into six subtypes, with Norway having ongoing epidemics of SAV subtypes 2 and 3. These two viral subtypes are present in largely distinct geographic regions of Norway, with SAV2 present in Trondelag, SAV3 in Rogaland, Sogn og Fjordane, and Hordaland, and Møre og Romsdal having outbreaks of both subtypes. To determine likely transmission routes of Norwegian SAV an established Nanopore amplicon sequencing approach was used in the current study. After confirming the accuracy of this approach for distinguishing subtype level co-infections of SAV2 and SAV3, a hypothetical possibility in regions of neighboring epidemics, twenty-four SAV3 genomes were sequenced to characterize the current genetic diversity of SAV3 in Norwegian aquaculture. Sequencing was performed on naturally infected heart tissues originating from a range of geographic locations sampled between 2016 and 2019. Phylogenetic analyses revealed that the currently active SAV3 strains sampled comprise several distinct lineages sharing an ancestor that existed ∼15 years ago (95% HPD, 12.51-17.7 years) and likely in Hordaland. At least five of these lineages have not shared a common ancestor for 7.85 years (95% HPD, 5.39-10.96 years) or more. Furthermore, the ancestor of the strains that were sampled outside of Hordaland (Sogn of Fjordane and Rogaland) existed less than 8 years ago, indicating a lack of long-term viral reservoirs in these counties. This evident lack of geographically distinct subclades is compatible with a source-sink transmission dynamic explaining the long-term movements of SAV around Norway. Such anthropogenic transport of the virus indicates that at least for sink counties, biosecurity strategies might be effective in mitigating the ongoing SAV epidemic. Finally, genomic analyses of SAV sequences were performed, offering novel insights into the prevalence of SAV genomes containing defective deletions. Overall, this study improves our understanding of the recent transmission dynamics and biology of the SAV epidemic affecting Norwegian aquaculture.
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Affiliation(s)
- Michael D. Gallagher
- School of Biological Sciences, University of Aberdeen, Aberdeen, United Kingdom
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Edinburgh, United Kingdom
| | | | | | | | - Iveta Matejusova
- Marine Laboratory, Marine Scotland Science, Aberdeen, United Kingdom
| | - Daniel J. Macqueen
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Edinburgh, United Kingdom
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7
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Shi W, Wang Y, Ren X, Gao S, Hua X, Guo M, Tang L, Xu Y, Ren T, Li Y, Liu M. EvaGreen-based real-time PCR assay for sensitive detection of salmonid alphavirus. Mol Cell Probes 2018; 39:7-13. [DOI: 10.1016/j.mcp.2018.03.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 03/10/2018] [Accepted: 03/15/2018] [Indexed: 10/17/2022]
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Abstract
Salmonid alphavirus (SAV), genus Alphavirus, family Togaviridae, is a single-stranded RNA virus affecting Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). It is known to be responsible for pancreas disease (PD) and sleeping disease (SD) which are increasing problems, causing high fish mortality and economic losses in the European aquaculture industry. Pancreas disease was first described in Atlantic salmon in Scotland in 1976 and a similar disease caused by the closely related sleeping disease virus was first described in rainbow trout in France. There have also been reports of salmonid alphavirus infections from other European countries, including Ireland, England, Norway, Germany, Italy, and Spain. Salmonid alphaviruses have been classified into six subtypes (SAV1–6). SAV1 and SAV4–6 cause pancreas disease in Atlantic salmon in Ireland or Scotland, SAV2 is the causative agent of sleeping disease in rainbow trout, and SAV3 has been detected in Atlantic salmon in Norway. The aim of this paper was to summarise current knowledge of infections caused by salmonid alphavirus and diagnostic methods including the newest techniques, and to briefly describe prevention from SAV infections by vaccination.
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9
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Moore LJ, Jarungsriapisit J, Nilsen TO, Stefansson S, Taranger GL, Secombes CJ, Morton HC, Patel S. Atlantic salmon adapted to seawater for 9 weeks develop a robust immune response to salmonid alphavirus upon bath challenge. FISH & SHELLFISH IMMUNOLOGY 2018; 74:573-583. [PMID: 29353080 DOI: 10.1016/j.fsi.2017.12.017] [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: 11/02/2017] [Revised: 12/09/2017] [Accepted: 12/11/2017] [Indexed: 06/07/2023]
Abstract
Pancreas disease (PD) caused by salmonid alphavirus (SAV) is the most serious viral disease in Norwegian aquaculture. Study of the immune response to SAV will aid preventative measures including vaccine development. The innate immune response was studied in Atlantic salmon infected by either bath immersion (BI) or by intra-muscular (i.m.) injection (IM) with SAV subtype 3, two and nine weeks after seawater transfer (Phases A and B respectively). Phase A results have been previously published (Moore et al., 2017) and Phase B results are presented here together with a comparison of results achieved in Phase A. There was a rapid accumulation of infected fish in the IM-B (IM Phase B) group and all fish sampled were SAV RNA positive by 7 dpi (days post infection). In contrast, only a few SAV RNA positive (infected) fish were identified at 14, 21 and 28 dpi in the BI-B (BI Phase B) group. Differences in the transcription of several immune genes were apparent when compared between the infected fish in the IM-B and BI-B groups. Transcription of the analysed genes peaked at 7 dpi in the IM-B group and at 14 dpi in the BI-B group. However, this latter finding was difficult to interpret due to the low prevalence of SAV positive fish in this group. Additionally, fish positive for SAV RNA in the BI-B group showed higher transcription of IL-1β, IFNγ and CXCL11_L1, all genes associated with the inflammatory response, compared to the IM-B group. Histopathological changes in the heart were restricted to the IM-B group, while (immune) cell filtration into the pancreas was observed in both groups. Compared to the Phase A fish that were exposed to SAV3 two weeks after seawater transfer, the Phase B fish in the current paper, showed a higher and more sustained innate immune gene transcription in response to the SAV3 infection. In addition, the basal transcription of several innate immune genes in non-infected control fish in Phase B (CT-B) was also significantly different when compared to Phase A control fish (CT-A).
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Affiliation(s)
- L J Moore
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway
| | - J Jarungsriapisit
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway; Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway
| | - T O Nilsen
- Uni Research Environment, Uni Research, Thormøhlensgt. 49B, 5006 Bergen, Norway
| | - S Stefansson
- Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway
| | - G L Taranger
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway
| | - C J Secombes
- Scottish Fish Immunology Research Centre, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland, UK
| | - H C Morton
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway
| | - S Patel
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway.
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10
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Wallace IS, McKay P, Murray AG. A historical review of the key bacterial and viral pathogens of Scottish wild fish. JOURNAL OF FISH DISEASES 2017; 40:1741-1756. [PMID: 28718925 DOI: 10.1111/jfd.12654] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 04/07/2017] [Accepted: 04/08/2017] [Indexed: 06/07/2023]
Abstract
Thousands of Scottish wild fish were screened for pathogens by Marine Scotland Science. A systematic review of published and unpublished data on six key pathogens (Renibacterium salmoninarum, Aeromonas salmonicida, IPNV, ISAV, SAV and VHSV) found in Scottish wild and farmed fish was undertaken. Despite many reported cases in farmed fish, there was a limited number of positive samples from Scottish wild fish, however, there was evidence for interactions between wild and farmed fish. A slightly elevated IPNV prevalence was reported in wild marine fish caught close to Atlantic salmon, Salmo salar L., farms that had undergone clinical IPN. Salmonid alphavirus was isolated from wild marine fish caught near Atlantic salmon farms with a SAV infection history. Isolations of VHSV were made from cleaner wrasse (Labridae) used on Scottish Atlantic salmon farms and VHSV was detected in local wild marine fish. However, these pathogens have been detected in wild marine fish caught remotely from aquaculture sites. These data suggest that despite the large number of samples taken, there is limited evidence for clinical disease in wild fish due to these pathogens (although BKD and furunculosis historically occurred) and they are likely to have had a minimal impact on Scottish wild fish.
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Affiliation(s)
- I S Wallace
- Marine Scotland Science, Marine Laboratory, Aberdeen, UK
| | - P McKay
- Marine Scotland Science, Marine Laboratory, Aberdeen, UK
| | - A G Murray
- Marine Scotland Science, Marine Laboratory, Aberdeen, UK
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11
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Shi W, Song A, Gao S, Wang Y, Tang L, Xu Y, Ren T, Li Y, Liu M. Rapid and sensitive detection of salmonid alphavirus using TaqMan real-time PCR. Mol Cell Probes 2017; 34:13-20. [PMID: 28433811 DOI: 10.1016/j.mcp.2017.04.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Revised: 04/17/2017] [Accepted: 04/18/2017] [Indexed: 11/29/2022]
Abstract
Salmonid alphavirus (SAV) infection has led to the spread of salmon pancreas disease (PD) and sleeping disease (SD) to salmonids in several countries in Europe, resulting in tremendous economic losses to the fish farming industry. Recently, with increases in the fish import trade, many countries in which SAV has been unreported, such as China, may be seriously threatened by these diseases. It is therefore necessary to develop efficient detection methods for the prevention and diagnosis of SAV infection. In this study, a rapid and sensitive TaqMan real-time PCR method was established and assessed for this purpose. A specificity assay showed no cross-reactions with other common RNA viruses. Regression analysis and standard curves calculated from the Ct values of 10-fold serial dilutions of the standard plasmid showed that the assay was highly reproducible over a wide range of RNA input concentrations. The real-time PCR assay was able to detect SAV at a concentration as low as 1.5 × 101 copies, indicating that it is 107 times more sensitive than the approved conventional RT-PCR method (detection limit, 1.5 × 107 copies) after use on the same samples. Assessment of infected fish samples showed that this assay has a higher sensitivity than the previously reported Q_nsP1 assay. Thus, this TaqMan real-time PCR assay provides a rapid, sensitive, and specific detection method for SAV, offering improved technical support for the clinical diagnosis and epidemiology of SAV.
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Affiliation(s)
- Wen Shi
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Aochen Song
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Shuai Gao
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Yuting Wang
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Lijie Tang
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Yigang Xu
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Tong Ren
- Beijing Entry-exit Inspection and Quarantine Bureau, Beijing 100026, People's Republic of China
| | - Yijing Li
- Northeast Agricultural University, Harbin 150030, People's Republic of China
| | - Min Liu
- Northeast Agricultural University, Harbin 150030, People's Republic of China.
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12
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Moore LJ, Jarungsriapisit J, Nilsen TO, Stefansson S, Taranger GL, Secombes CJ, Morton HC, Patel S. Immune gene profiles in Atlantic salmon (salmo salar L.) post-smolts infected with SAV3 by bath-challenge show a delayed response and lower levels of gene transcription compared to injected fish. FISH & SHELLFISH IMMUNOLOGY 2017; 62:320-331. [PMID: 28137651 DOI: 10.1016/j.fsi.2017.01.034] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Revised: 01/21/2017] [Accepted: 01/23/2017] [Indexed: 06/06/2023]
Abstract
Salmonid alphavirus (SAV) causes pancreatic disease (PD) in salmonids in Northern Europe which results in large economic losses within the aquaculture industry. In order to better understand the underlying immune mechanisms during a SAV3 infection Atlantic salmon post-smolts were infected by either i.m.-injection or bath immersion and their immune responses compared. Analysis of viral loads showed that by 14 dpi i.m.-injected and bath immersion groups had 95.6% and 100% prevalence respectively and that both groups had developed the severe pathology typical of PD. The immune response was evaluated by using RT-qPCR to measure the transcription of innate immune genes involved in the interferon (IFN) response as well as genes associated with inflammation. Our results showed that IFNa transcription was only weakly upregulated, especially in the bath immersion group. Despite this, high levels of the IFN-stimulated genes (ISGs) such as Mx and viperin were observed. The immune response in the i.m.-injected group as measured by immune gene transcription was generally faster, and more pronounced than the response in the bath immersion group, especially at earlier time-points. The response in the bath immersion group started later as expected and appeared to last longer often exceeding the response in the i.m-injected fish at later time-points. High levels of transcription of many genes indicative of an active innate immune response were present in both groups.
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Affiliation(s)
- L J Moore
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway
| | - J Jarungsriapisit
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway; Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway
| | - T O Nilsen
- Uni Research Environment, Uni Research, Thormøhlensgt, 49B 5006 Bergen, Norway
| | - S Stefansson
- Department of Biology, University of Bergen, P.O. Box 7803, 5020 Bergen, Norway
| | - G L Taranger
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway
| | - C J Secombes
- Scottish Fish Immunology Research Centre, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland, UK
| | - H C Morton
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway
| | - S Patel
- Institute of Marine Research, P.O. Box 1870, Nordnes, 5817 Bergen, Norway.
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13
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Powell MD, Yousaf MN. Cardiovascular Effects of Disease: Parasites and Pathogens. FISH PHYSIOLOGY 2017. [DOI: 10.1016/bs.fp.2017.09.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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14
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Jansen MD, Bang Jensen B, McLoughlin MF, Rodger HD, Taksdal T, Sindre H, Graham DA, Lillehaug A. The epidemiology of pancreas disease in salmonid aquaculture: a summary of the current state of knowledge. JOURNAL OF FISH DISEASES 2017; 40:141-155. [PMID: 27136332 DOI: 10.1111/jfd.12478] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 02/12/2016] [Accepted: 02/18/2016] [Indexed: 05/13/2023]
Abstract
Pancreas disease (PD) is a viral disease caused by Salmonid alphavirus (SAV) that affects farmed Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss (Walbaum)) in the seawater phase. Since its first description in Scotland in 1976, a large number of studies have been conducted relating to the disease itself and to factors contributing to agent spread and disease occurrence. This paper summarizes the currently available, scientific information on the epidemiology of PD and its associated mitigation and control measures. Available literature shows infected farmed salmonids to be the main reservoir of SAV. Transmission between seawater sites occurs mainly passively by water currents or actively through human activity coupled with inadequate biosecurity measures. All available information suggests that the current fallowing procedures are adequate to prevent agent survival within the environment through the fallowing period and thus that a repeated disease outbreak at the same site is due to a new agent introduction. There has been no scientific evaluation of currently used on-site biosecurity measures, and there is limited information on the impact of available mitigation measures and control strategies.
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Affiliation(s)
- M D Jansen
- Norwegian Veterinary Institute, Oslo, Norway
| | | | | | - H D Rodger
- Vet-Aqua International, Oranmore, Ireland
| | - T Taksdal
- Norwegian Veterinary Institute, Oslo, Norway
| | - H Sindre
- Norwegian Veterinary Institute, Oslo, Norway
| | - D A Graham
- Animal Health Ireland, Carrick on Shannon, Ireland
| | - A Lillehaug
- Norwegian Veterinary Institute, Oslo, Norway
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15
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Pettersen J, Brynildsrud O, Huseby R, Rich K, Aunsmo A, Bang BJ, Aldrin M. The epidemiological and economic effects from systematic depopulation of Norwegian marine salmon farms infected with pancreas disease virus. Prev Vet Med 2016; 132:113-124. [DOI: 10.1016/j.prevetmed.2016.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Revised: 08/31/2016] [Accepted: 09/01/2016] [Indexed: 10/21/2022]
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16
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Simons J, Bruno DW, Ho YM, Murray W, Matejusova I. Common dab, Limanda limanda (L.), as a natural carrier of salmonid alphavirus (SAV) from waters off north-west Ireland. JOURNAL OF FISH DISEASES 2016; 39:507-510. [PMID: 25865360 DOI: 10.1111/jfd.12376] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 02/27/2015] [Indexed: 06/04/2023]
Affiliation(s)
- J Simons
- Marine Scotland Science, Aberdeen, UK
| | - D W Bruno
- Marine Scotland Science, Aberdeen, UK
| | - Y-M Ho
- Marine Scotland Science, Aberdeen, UK
| | - W Murray
- Marine Scotland Science, Aberdeen, UK
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Hjortaas MJ, Jensen BB, Taksdal T, Olsen AB, Lillehaug A, Trettenes E, Sindre H. Genetic characterization of salmonid alphavirus in Norway. JOURNAL OF FISH DISEASES 2016; 39:249-57. [PMID: 25683753 DOI: 10.1111/jfd.12353] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 12/17/2014] [Accepted: 12/17/2014] [Indexed: 05/13/2023]
Abstract
Pancreas disease (PD), caused by salmonid alphavirus subtype 3 (SAV3), emerged in Norwegian aquaculture in the 1980s and is now endemic along the south-western coast. In 2011, the first cases of PD caused by marine salmonid alphavirus subtype 2 (SAV2) were reported. This subtype has spread rapidly among the fish farms outside the PD-endemic zone and is responsible for disease outbreaks at an increasing numbers of sites. To describe the geographical distribution of salmonid alphavirus (SAV), and to assess the time and site of introduction of marine SAV2 to Norway, an extensive genetic characterization including more than 200 SAV-positive samples from 157 Norwegian marine production sites collected from May 2007 to December 2012 was executed. The first samples positive for marine SAV2 originated from Romsdal, in June 2010. Sequence analysis of the E2 gene revealed that all marine SAV2 included in this study were nearly identical, suggesting a single introduction into Norwegian aquaculture. Further, this study provides evidence of a separate geographical distribution of two subtypes in Norway. SAV3 is present in south-western Norway, and marine SAV2 circulates in north-western and Mid-Norway, a geographical area which since 2010 constitutes the endemic zone for marine SAV2.
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Affiliation(s)
| | | | - T Taksdal
- Norwegian Veterinary Institute, Oslo, Norway
| | - A B Olsen
- Norwegian Veterinary Institute, Bergen, Norway
| | - A Lillehaug
- Norwegian Veterinary Institute, Oslo, Norway
| | - E Trettenes
- Norwegian Veterinary Institute, Oslo, Norway
| | - H Sindre
- Norwegian Veterinary Institute, Oslo, Norway
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18
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Murray AG. Does the use of salmon frames as bait for lobster/crab creel fishing significantly increase the risk of disease in farmed salmon in Scotland? Prev Vet Med 2015; 120:357-66. [DOI: 10.1016/j.prevetmed.2015.04.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 04/28/2015] [Accepted: 04/30/2015] [Indexed: 01/02/2023]
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19
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Gonen S, Baranski M, Thorland I, Norris A, Grove H, Arnesen P, Bakke H, Lien S, Bishop SC, Houston RD. Mapping and validation of a major QTL affecting resistance to pancreas disease (salmonid alphavirus) in Atlantic salmon (Salmo salar). Heredity (Edinb) 2015; 115:405-14. [PMID: 25990876 PMCID: PMC4611234 DOI: 10.1038/hdy.2015.37] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 02/22/2015] [Accepted: 03/23/2015] [Indexed: 01/01/2023] Open
Abstract
Pancreas disease (PD), caused by a salmonid alphavirus (SAV), has a large negative economic and animal welfare impact on Atlantic salmon aquaculture. Evidence for genetic variation in host resistance to this disease has been reported, suggesting that selective breeding may potentially form an important component of disease control. The aim of this study was to explore the genetic architecture of resistance to PD, using survival data collected from two unrelated populations of Atlantic salmon; one challenged with SAV as fry in freshwater (POP 1) and one challenged with SAV as post-smolts in sea water (POP 2). Analyses of the binary survival data revealed a moderate-to-high heritability for host resistance to PD in both populations (fry POP 1 h2~0.5; post-smolt POP 2 h2~0.4). Subsets of both populations were genotyped for single nucleotide polymorphism markers, and six putative resistance quantitative trait loci (QTL) were identified. One of these QTL was mapped to the same location on chromosome 3 in both populations, reaching chromosome-wide significance in both the sire- and dam-based analyses in POP 1, and genome-wide significance in a combined analysis in POP 2. This independently verified QTL explains a significant proportion of host genetic variation in resistance to PD in both populations, suggesting a common underlying mechanism for genetic resistance across lifecycle stages. Markers associated with this QTL are being incorporated into selective breeding programs to improve PD resistance.
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Affiliation(s)
- S Gonen
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian, UK
| | | | - I Thorland
- Akvaforsk Genetics Center AS, Sunndalsøra, Norway
| | | | - H Grove
- Department of Animal and Aquacultural Sciences and Centre for Integrative Genetics, Norwegian University of Life Sciences, Ås, Norway
| | | | - H Bakke
- SalmoBreed AS, Bergen, Norway
| | - S Lien
- Department of Animal and Aquacultural Sciences and Centre for Integrative Genetics, Norwegian University of Life Sciences, Ås, Norway
| | - S C Bishop
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian, UK
| | - R D Houston
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian, UK
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20
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Cano I, Joiner C, Bayley A, Rimmer G, Bateman K, Feist SW, Stone D, Paley R. An experimental means of transmitting pancreas disease in Atlantic salmon Salmo salar L. fry in freshwater. JOURNAL OF FISH DISEASES 2015; 38:271-281. [PMID: 25297529 DOI: 10.1111/jfd.12310] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Revised: 08/05/2014] [Accepted: 08/06/2014] [Indexed: 06/04/2023]
Abstract
A challenge model for pancreas disease in Atlantic salmon, Salmo salar L. fry, was developed comparing two salmonid alphavirus (SAV) subtypes: SAV1 and SAV5. Viral doses of 3 × 10(5) TCID50 mL(-1) for SAV1 and 3 × 10(4) for SAV5 were tested in triplicate tanks, each containing 450 salmon fry. Cumulative mortalities of 1.2% were recorded. Titres of virus recovered from the mortalities ranged from 10(2) to 10(7) TCID50 mL(-1) . Fry were sampled at 3, 5 and 7.5 weeks post-challenge. Sampling after 3 weeks revealed a high prevalence of infection in the absence of clinical signs, and infectious virus was recovered from 80% and 43% of sampled fry infected with SAV1 and SAV5, respectively. After 5 weeks pancreas, heart and red skeletal muscle lesions were generally observed, whilst degeneration in white skeletal muscle was observed only in fish infected with SAV1. In situ hybridisation confirmed the presence of viral genome in infected pancreas, heart and muscle. After 7.5 weeks, infectious virus (both isolates) was recovered from 13.3% of the fish sampled, with a viral titre of 10(2) TCID50 mL(-1) . Clearly, salmon fry are susceptible to SAV infection and pancreas disease.
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Affiliation(s)
- I Cano
- Aquatic Animal Disease, Centre for Environment, Fisheries and Aquaculture Science, The Nothe Weymouth, Dorset, UK
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21
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Graham DA, Rowley HR, Frost P. Cross-neutralization studies with salmonid alphavirus subtype 1-6 strains: results with sera from experimental studies and natural infections. JOURNAL OF FISH DISEASES 2014; 37:683-91. [PMID: 23957811 DOI: 10.1111/jfd.12167] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Revised: 07/15/2013] [Accepted: 07/16/2013] [Indexed: 05/13/2023]
Abstract
The serological reactivity between strains of each of the six currently genetically defined subtypes of salmonid alphavirus (SAV) was examined by comparison of homologous and heterologous virus neutralization titres on sera from experimentally infected fish. With the exception of the level of SAV subtype 6 neutralization by heterologous sera, good cross-neutralization was detected between all subtypes, albeit with variation in geometric mean titres when each subtype-specific serum set was tested against the panel of virus subtypes. A similar pattern was evident with field sera, except that heterologous neutralization of the SAV6 strain was more evident. In only 23% of available pairwise comparisons was the homologous titre recorded with an experimentally derived serum fourfold or greater than the heterologous titre, and in only two instances was this difference demonstrated in both directions. No virus strains consistently met the old serology-based criteria (Sub-committee on Inter-relationships Among Catalogued Alphaviruses) to be considered separate subtypes within an alphavirus species. Only when testing with an SAV subtype-2-specific monoclonal antibody was a major difference between homologous and heterologous neutralization capacity evident. These results provide new direct or indirect information in terms of SAV classification, vaccine efficacy and the selection and validation of reagents for serological and immunological diagnostic purposes.
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Affiliation(s)
- D A Graham
- Fish Diseases Unit, Agrifood and Biosciences Institute, Stormont, UK
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22
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McCleary S, Giltrap M, Henshilwood K, Ruane NM. Detection of salmonid alphavirus RNA in Celtic and Irish Sea flatfish. DISEASES OF AQUATIC ORGANISMS 2014; 109:1-7. [PMID: 24781791 DOI: 10.3354/dao02719] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Pancreas disease (PD) caused by the salmonid alphavirus (SAV) has been the most significant cause of mortalities in Irish farmed salmon Salmo salar L. over the past decade. SAV is a single-strand positive-sense RNA virus, originally thought to be unique to salmonids, but has recently been detected using real-time RT-PCR in a number of wild non-salmonid fish. In the present report, 610 wild flatfish (common dab Limanda limanda, plaice Pleuronectes platessa and megrim Lepidorhombus whiffiagonis) were caught from the Irish and Celtic Seas and screened for SAV using real-time RT-PCR and sequencing. In general, a very low prevalence was recorded in common dab and plaice, except for 1 haul in Dublin Bay where 25% of common dab were SAV-positive. SAV sequence analysis supported the fact that real-time RT-PCR detections were specific and further characterised the detected viruses within SAV Subtype I, the predominant subtype found in farmed salmon in Ireland.
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Affiliation(s)
- S McCleary
- Marine Institute, Rinville, Oranmore, Galway, Ireland
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23
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Hikke MC, Verest M, Vlak JM, Pijlman GP. Salmonid alphavirus replication in mosquito cells: towards a novel vaccine production system. Microb Biotechnol 2014; 7:480-4. [PMID: 24418177 PMCID: PMC4229328 DOI: 10.1111/1751-7915.12100] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 10/14/2013] [Accepted: 10/21/2013] [Indexed: 11/28/2022] Open
Abstract
Salmonid alphavirus (SAV) causes pancreas disease and sleeping disease in Atlantic salmon (Salmosalar) and rainbow trout (Oncorhynchus mykiss) and confers a major burden to the aquaculture industry. A commercial inactivated whole virus vaccine propagated in a salmon cell line at low temperature provides effective protection against SAV infections. Alphaviruses (family Togaviridae) are generally transmitted between vertebrate hosts via blood-sucking arthropod vectors, typically mosquitoes. SAV is unique in this respect because it can be transmitted directly from fish to fish and has no known invertebrate vector. Here, we show for the first time that SAV is able to complete a full infectious cycle within arthropod cells derived from the Asian tiger mosquito Aedes albopictus. Progeny virus is produced in C6/36 and U4.4. cells in a temperature-dependent manner (at 15°C but not at 18°C), can be serially passaged and remains infectious to salmonid Chinook salmon embryo cells. This suggests that SAV is not a vertebrate-restricted alphavirus after all and may have the potential to replicate in invertebrates. The current study also shows the ability of SAV to be propagated in mosquito cells, thereby possibly providing an alternative SAV production system for vaccine applications.
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Affiliation(s)
- Mia C Hikke
- Wageningen University, Laboratory of Virology, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands
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24
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Braceland M, Bickerdike R, Tinsley J, Cockerill D, Mcloughlin M, Graham D, Burchmore R, Weir W, Wallace C, Eckersall P. The serum proteome of Atlantic salmon, Salmo salar, during pancreas disease (PD) following infection with salmonid alphavirus subtype 3 (SAV3). J Proteomics 2013; 94:423-36. [PMID: 24145143 PMCID: PMC3878379 DOI: 10.1016/j.jprot.2013.10.016] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 09/27/2013] [Accepted: 10/11/2013] [Indexed: 02/07/2023]
Abstract
Salmonid alphavirus is the aetological agent of pancreas disease (PD) in marine Atlantic salmon, Salmo salar, and rainbow trout, Oncorhynchus mykiss, with most outbreaks in Norway caused by SAV subtype 3 (SAV3). This atypical alphavirus is transmitted horizontally causing a significant economic impact on the aquaculture industry. This histopathological and proteomic study, using an established cohabitational experimental model, investigated the correlation between tissue damage during PD and a number of serum proteins associated with these pathologies in Atlantic salmon. The proteins were identified by two-dimensional electrophoresis, trypsin digest and peptide MS/MS fingerprinting. A number of humoral components of immunity which may act as biomarkers of the disease were also identified. For example, creatine kinase, enolase and malate dehydrogenase serum concentrations were shown to correlate with pathology during PD. In contrast, hemopexin, transferrin, and apolipoprotein, amongst others, altered during later stages of the disease and did not correlate with tissue pathologies. This approach has given new insight into not only PD but also fish disease as a whole, by characterisation of the protein response to infection, through pathological processes to tissue recovery. BIOLOGICAL SIGNIFICANCE Salmonid alphavirus causes pancreas disease (PD) in Atlantic salmon, Salmo salar, and has a major economic impact on the aquaculture industry. A proteomic investigation of the change to the serum proteome during PD has been made with an established experimental model of the disease. Serum proteins were identified by two-dimensional electrophoresis, trypsin digest and peptide MS/MS fingerprinting with 72 protein spots being shown to alter significantly over the 12week period of the infection. The concentrations of certain proteins in serum such as creatine kinase, enolase and malate dehydrogenase were shown to correlate with tissue pathology while other proteins such as hemopexin, transferrin, and apolipoprotein, altered in concentration during later stages of the disease and did not correlate with tissue pathologies. The protein response to infection may be used to monitor disease progression and enhance understanding of the pathology of PD.
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Affiliation(s)
- M. Braceland
- Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Bearsden Rd, Glasgow, G61 1QH, Scotland, UK
| | - R. Bickerdike
- BioMar Ltd., North Shore Road, Grangemouth Docks, Grangemouth, FK3 8UL, Scotland, UK
| | - J. Tinsley
- BioMar Ltd., North Shore Road, Grangemouth Docks, Grangemouth, FK3 8UL, Scotland, UK
| | - D. Cockerill
- Marine Harvest Scotland, Farms Office Blar Mhor Industrial Estate, Fort William, PH33 7PT, Scotland, UK
| | - M.F. Mcloughlin
- Aquatic Vet Services, 35 Cherryvalley Pk, Belfast, BT5 6PN, Northern Ireland, UK
| | - D.A. Graham
- Fish Diseases Unit, Agri-food and Biosciences Institute, Stoney Rd, Stormont, Belfast, BT4 3SD, Northern Ireland, UK
| | - R.J. Burchmore
- Institute of Infection, Immunity & Inflammation, University of Glasgow, Bearsden Rd Glasgow, G61 1QH, Scotland, UK
| | - W. Weir
- Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Bearsden Rd, Glasgow, G61 1QH, Scotland, UK
| | - C. Wallace
- VESO Vikan, Aquamedical Contract Research, Vikan, N-7800 Namsos, Norway
| | - P.D. Eckersall
- Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Bearsden Rd, Glasgow, G61 1QH, Scotland, UK
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Karlsen M, Gjerset B, Hansen T, Rambaut A. Multiple introductions of salmonid alphavirus from a wild reservoir have caused independent and self-sustainable epizootics in aquaculture. J Gen Virol 2013; 95:52-59. [PMID: 24062534 DOI: 10.1099/vir.0.057455-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Salmonid alphavirus (SAV) causes infections in farmed Atlantic salmon and rainbow trout in Europe. Genetic diversity exists among SAV strains from farmed fish and six subtypes have been proposed based on genetic distance. Here, we used six full-genome sequences and 71 partial sequences of the structural ORF to estimate the evolutionary rate of SAV. The rate, 2.13×10(-4) nt substitutions per site per year, was further used to date evolutionary events in a Bayesian phylogenetic framework. The comparison of these dates with known historical events suggested that all six subtypes diverged prior to the twentieth century, earlier than the first attempts to introduce and farm rainbow trout in Europe. The subtypes must therefore have existed in a wild reservoir, as yet unidentified. The strains of each subtype, with the exception of subtype 2, have a common ancestor that existed after the 1970s - the start of modern farming of Atlantic salmon. These ancestors are likely to represent the independent introductions to farmed fish populations from the wild reservoir. The subtypes have developed subsequently into self-sustainable epizootics. The most parsimonious phylogeographic reconstruction suggested that the location of the wild reservoir is in or around the North Sea. After the initial introductions to aquaculture, further transmission of SAV was likely related to the industry infrastructure. This was exemplified by the finding of genetically identical subtype 2 and 3 strains separated by large geographical distances, as well as genetically distinct co-circulating lineages within the same geographical area.
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Affiliation(s)
| | - Britt Gjerset
- Norwegian Veterinary Institute, Pb 750 Sentrum, 0106 Oslo, Norway
| | - Tove Hansen
- PHARMAQ AS, Harbitzalléen 2a, 0275 Oslo, Norway
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26
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Petterson E, Stormoen M, Evensen Ø, Mikalsen AB, Haugland Ø. Natural infection of Atlantic salmon (Salmo salar L.) with salmonid alphavirus 3 generates numerous viral deletion mutants. J Gen Virol 2013; 94:1945-1954. [PMID: 23704276 DOI: 10.1099/vir.0.052563-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Salmon pancreas disease virus (SPDV) also referred to as salmonid alphavirus (SAV) is a virus causing pancreas disease in Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss). Although the virus causes an economically important disease, relatively few full-length genome sequences of SAV strains are currently available. Here, we report full-length genome sequences of nine SAV3 strains from sites farming Atlantic salmon geographically spread along the Norwegian coastline. The virus genomes were sequenced directly from infected heart tissue, to avoid culture selection bias. Sequence analysis confirmed a high level of sequence identity within SAV3 strains, with a mean nucleotide diversity of 0.11 %. Sequence divergence was highest in 6K and E2, while lowest in the capsid protein and the non-structural proteins (nsP4 and nsP2). This study reports for the first time that numerous defective viruses containing genome deletions are generated during natural infection with SAV. Deletions occurred in all virus strains and were not distributed randomly throughout the genome but instead tended to aggregate in certain areas. We suggest imprecise homologous recombination as an explanation for generation of defective viruses with genome deletions. The presence of such viruses, provides a possible explanation for the difficulties in isolating SAV in cell culture. Primary virus isolation was successfully achieved for only two of eight strains, despite extensive attempts using three different cell lines. Both SAV isolates were easily propagated further and concomitant viral deletion mutants present in clinically infected heart tissue were maintained following serial passage in CHH-1 cells.
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Affiliation(s)
- Elin Petterson
- Norwegian School of Veterinary Science, Department of Basic Sciences and Aquatic Medicine, P.O. Box 8146 Dep., 0033 Oslo Norway
| | - Marit Stormoen
- Norwegian School of Veterinary Science, Department of Basic Sciences and Aquatic Medicine, P.O. Box 8146 Dep., 0033 Oslo Norway
| | - Øystein Evensen
- Norwegian School of Veterinary Science, Department of Basic Sciences and Aquatic Medicine, P.O. Box 8146 Dep., 0033 Oslo Norway
| | - Aase B Mikalsen
- Norwegian School of Veterinary Science, Department of Basic Sciences and Aquatic Medicine, P.O. Box 8146 Dep., 0033 Oslo Norway
| | - Øyvind Haugland
- Norwegian School of Veterinary Science, Department of Basic Sciences and Aquatic Medicine, P.O. Box 8146 Dep., 0033 Oslo Norway
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