Transmission of infectious salmon anaemia virus (ISAV) in farmed populations of Atlantic salmon (Salmo salar)

Nylund, Are; Plarre, Heidrun; Karlsen, Marius; Fridell, F.; Ottem, Karl Fredrik; Bratland, A.; Sæther, Per Anton

doi:10.1007/s00705-006-0825-9

Cited by 72 publications

(125 citation statements)

References 91 publications

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“…The shift in virulence from ISAV-HPR0 to a disease-causing ISAV has been suggested to be a stochastic event dependent on the replication rate of the virus and the time available for virulence mutations to occur and accumulate [21]. Studies in fish and mammals have demonstrated that stress can play a key role in facilitating an increased viral replication rate because of a weakened immune response [54,55].…”

Section: Discussionmentioning

confidence: 99%

“…The ORF of the HE gene of the 11 ISAV-HPR0 variants (see below) was sequenced and aligned with other publicly available sequences of the same segment [19,21,[32][33][34][35] using CLUSTAL X [63]. Identical sequences were identified with only a single representative type retained in the dataset to reduce subsequent analytical bias.…”

Section: Molecular Phylogenetic Analysis Of the He Genementioning

confidence: 99%

“…Putatively uncultivable non-virulent ISAV variants (ISAV-HPR0) are characterized by an HE protein carrying a full-length highly polymorphic region (HPR) composed of at least 35 amino acids just upstream of the transmembrane domain [15][16][17][18][19]. All currently described pathogenic ISAV isolates associated with ISA disease have deletions in the HPR with over 30 different HPR-deleted subtypes identified in Europe, North America and Chile [16][17][18][19][20][21][22]. Sequencing and functional characterization further suggest both HPR-deletion and a Q 266 L substitution, or insertion adjacent to the cleavage site in the F protein influences ISAV virulence [22], by promoting viral fusion and the activation of proteolytic cleavage [23,24].…”

Section: Introductionmentioning

confidence: 99%

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First field evidence of the evolution from a non-virulent HPR0 to a virulent HPR-deleted infectious salmon anaemia virus

Christiansen

McBeath

Aamelfot

et al. 2017

Journal of General Virology

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The putatively non-virulent subtype of infectious salmon anaemia virus (ISAV), ISAV-HPR0, is proposed to act as a progenitor and reservoir for all virulent ISAVs and thus represent a potential risk factor for the emergence of infectious salmon anaemia (ISA) disease. Here, we provide the first evidence of genetic and functional evolution from an ISAV-HPR0 variant (FO/07/12) to a low-virulent ISAV virus (FO/121/14) in a Faroese Atlantic salmon marine farm. The FO/121/14 virus infection was not associated with specific clinical signs of ISA and was confined to a single net-pen, while various ISAV-HPR0 subtypes were found circulating in most epidemiologically linked marine and freshwater farms. Sequence analysis of all eight segments revealed that the FO/121/14 virus was identical, apart from a substitution in the fusion (F) gene (Q 266 L) and a deletion in the haemagglutinin-esterase (HE) gene, to the FO/07/12 variant from a freshwater farm, which supplied smolts exclusively to the FO/121/14-positive net-pen. An immersion challenge with the FO/121/14 virus induced a systemic infection in Atlantic salmon associated with a low mortality and mild clinical signs confirming its low pathogenicity. Our results demonstrate that mutations in the F protein and deletions in the highly polymorphic region (HPR) of the HE protein represent a minimum requirement for ISAV to gain virulence and to switch cell tropism from a localized epithelial infection to a systemic endotheliotropic infection. This documents that ISAV-HPR0 represents a reservoir and risk factor for the emergence of ISA disease.

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Section: Discussionmentioning

confidence: 99%

Section: Molecular Phylogenetic Analysis Of the He Genementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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First field evidence of the evolution from a non-virulent HPR0 to a virulent HPR-deleted infectious salmon anaemia virus

Christiansen

McBeath

Aamelfot

et al. 2017

Journal of General Virology

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“…comm. ), while the 1998-1999 virus was of genogroup 3 (Nylund et al 2007) and mortality took longer to occur in salmon experimentally challenged with the 2008 virus (K. Urquhart unpubl. data).…”

Section: Origins Of the Outbreakmentioning

confidence: 99%

Epidemiological investigation into the re-emergence and control of an outbreak of infectious salmon anaemia in the Shetland Islands, Scotland

Murray¹,

Munro²,

Wallace³

et al. 2010

Dis. Aquat. Org.

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Infectious salmon anaemia (ISA) is an orthomyxoviral disease, primarily affecting marine-phase farmed Atlantic salmon, which can result in high levels of mortality. ISA first emerged in Norway in the 1980s and subsequently has occurred in Canada, the USA, the Faeroe Islands and Chile. An outbreak occurred in Scotland in 1998-1999, but was eradicated at a cost of over £20M. The epidemiology of a new outbreak of ISA in the Scottish Shetland Islands during 2008-2009 is described. Six sites have been confirmed ISA-positive. Spread of the virus via transport of fish between marine sites, harvest vessels, smolts and wild fish appears to have been of little or no importance, with spread primarily associated with marine water currents. The use of management areas by Marine Scotland to control the event appears to have been effective in restricting spread to a small area. This localised outbreak contrasts with the 1998-1999 outbreak that spread over a wide geographic area with transported fish and harvest vessels. The development and application of industry codes of good practice, good husbandry and biosecurity practices, limited marine site-to-site movement of live fish and improved disinfection of vessels and processing plant waste that occurred subsequent to the 1998-1999 outbreak may explain the localised spread of infection in [2008][2009]. Depopulation of confirmed sites has been achieved within 7 wk (mean = 3.7 wk); however, it is likely that subclinical infection persisted undetected for months on at least 1 site. The origin of the 2008-2009 outbreak remains unknown. Potential sources include evolution from a local reservoir of infection or importation. Synchronous fallowing of management areas, with good husbandry and biosecurity, reduces the risk of ISA recurring. Movement of fish between sites in different management areas represents the greatest risk of regional-scale spread, should this occur.KEY WORDS: Infectious salmon anaemia · ISA · Epidemiology · Control · Eradication · Hydrodynamics · Harvest · Scotland Resale or republication not permitted without written consent of the publisherDis Aquat Org 91: [189][190][191][192][193][194][195][196][197][198][199][200] 2010 behind ISA spread and how current Scottish fish farming structures and practices led to the spatial limitation of such spread, thus creating the conditions under which ISA could be controlled and eradicated.In 2008, Scotland produced 128 606 metric tonnes (t) of farmed Atlantic salmon from 257 marine sites and 2628 t of sea-farmed rainbow trout Oncorhynchus mykiss from 9 sites (Walker 2009). A further 311 t of brown and sea trout (both Salmo trutta) were also produced, but separate statistics are not published for marine and freshwater farms. (Both O. mykiss and S. trutta can carry the virus but do not develop clinical ISA [OIE 2009]). A third of Scottish salmon production (42 593 t) came from the Shetland Islands.Scottish salmon production is divided for the purposes of disease control into management areas (MAs) (Marine Scotland ...

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“…(Nylund et al 1993) and high levels of sea lice infestation have been suggested with major severity of ISA outbreaks in an expert-opinion based study (Gustafson et al 2005). Although vertical transmission has been suggested (Nylund et al 2007), there is little evidence of transmission via gonadal products.…”

Section: Introductionmentioning

confidence: 99%

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile

Mardones¹,

Pérez²,

Carpenter³

2009

Dis. Aquat. Org.

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Reports from surveillance activities were analyzed to determine the epidemiology of the re-emergence of infectious salmon anemia virus (ISAV) in Atlantic salmon farms in Chile. The epidemic and spatial and spatiotemporal patterns were described, taking into account commercial compartmentalization of the farms. During the 64 wk study period, 76 ISAV-infected salmon farms, representing 17 companies, were reported in 65% of the management geographic zones of the 10th region in southern Chile. Approximately 20% of the farms at risk became infected, with the incidence rate increasing slightly over time. Results from epidemic analyses and observed spatial and spatiotemporal patterns suggested an initial dispersal and subsequent clustering of cases around the index case (IC) in a propagated epidemic mode. Results suggested that delayed depopulation may have been a key factor in the spread and persistence of ISAV. Clustering of cases supported the assumption that passive transmission in seawater from ISAV-infected farms (proximity) is a critical factor in controlling disease. The re-emergence of ISAV in Chile has resulted in one of the largest ISAV epidemics reported in the world and this study generates new hypotheses and provides useful information for spatial disease control planning in salmon farming areas.

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Transmission of infectious salmon anaemia virus (ISAV) in farmed populations of Atlantic salmon (Salmo salar)

Cited by 72 publications

References 91 publications

First field evidence of the evolution from a non-virulent HPR0 to a virulent HPR-deleted infectious salmon anaemia virus

First field evidence of the evolution from a non-virulent HPR0 to a virulent HPR-deleted infectious salmon anaemia virus

Epidemiological investigation into the re-emergence and control of an outbreak of infectious salmon anaemia in the Shetland Islands, Scotland

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile

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