Multiple passage of infectious salmon anaemia virus in rainbow trout, <i><scp>O</scp>ncorhynchus mykiss</i> (<scp>W</scp>albaum), did not induce increased virus load

Olsen, Christel M.; Braaen, Stine; Falk, K. George; Rimstad, Espen

doi:10.1111/j.1365-2761.2012.01403.x

Cited by 5 publications

(4 citation statements)

References 45 publications

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“…While no evidence of causality exists, the ability to elute from erythrocytes appears to relate inversely to the susceptibility to disease. Rainbow trout can sustain ISAV infection [18,19], yet experimental infection does not appear to induce signs of ISA in this species, with the exception of a single study where ISA-like disease was observed in a few family groups [19][20][21]. Furthermore, the one reported case of natural ISAV infection in rainbow trout was not associated with disease [18].…”

Section: Introductionmentioning

confidence: 87%

Salmon Erythrocytes Sequester Active Virus Particles in Infectious Salmon Anaemia

Hol

Aamelfot

Sønstevold

et al. 2022

Viruses

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Infectious salmon anaemia virus (ISAV) binds circulating Atlantic salmon erythrocytes, but the relevance of this interaction for the course of infection and development of disease remains unclear. We here characterise ISAV-erythrocyte interactions in experimentally infected Atlantic salmon and show that ISAV-binding to erythrocytes is common and precedes the development of disease. Viral RNA and infective particles were enriched in the cellular fraction of blood. While erythrocyte-associated ISAV remained infectious, erythrocytes dose-dependently limited the infection of cultured cells. Surprisingly, immunostaining of blood smears revealed expression of ISAV proteins in a small fraction of erythrocytes in one of the examined trials, confirming that ISAV can be internalised in this cell type and engage the cellular machinery in transcription and translation. However, viral protein expression in erythrocytes was rare and not required for development of disease and mortality. Furthermore, active transcription of ISAV mRNA was higher in tissues than in blood, supporting the assumption that ISAV replication predominantly takes place in endothelial cells. In conclusion, Atlantic salmon erythrocytes bind ISAV and sequester infective virus particles during infection, but do not appear to significantly contribute to ISAV replication. We discuss the implications of our findings for infection dynamics and pathogenesis of infectious salmon anaemia.

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Section: Introductionmentioning

confidence: 87%

Salmon Erythrocytes Sequester Active Virus Particles in Infectious Salmon Anaemia

Hol

Aamelfot

Sønstevold

et al. 2022

Viruses

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“…The TaqMan assay (PE Applied Biosystems) was used for qPCR with an input of 5 μl diluted cDNA (equivalent to 15 ng RNA used in cDNA synthesis) per reaction in a total reaction volume of 13 μl. Primers and probe targeting ISAV genomic segment 8 were used as described earlier (Olsen et al, 2012 ). The qPCR reaction conditions were 300 nM primer, 200 nM probe, 6.5 μl TaqMan®.…”

Section: Methodsmentioning

confidence: 99%

Triploid Atlantic salmon (Salmo salar) may have increased risk of primary field outbreaks of infectious salmon anaemia

Aunsmo

Martinsen²,

Bruheim

et al. 2022

Journal of Fish Diseases

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The impact that escaped farmed fish may have on wild populations is of major concern for Atlantic salmon (Salmo salar) farming. Triploid fish, being infertile, were originally introduced to mitigate the genetic impact of escaped fish. In the recent years, an increase in the number of infectious salmon anaemia (ISA) outbreaks in Norway has been observed, mainly in the northern parts, which is also where farming of triploid fish has been licensed. The present study investigated the susceptibility of triploid Atlantic salmon to ISA both by field observations and experimental infections. Based on field observations, we found an increased susceptibility, with 9.4 increased odds to primary ISA outbreaks in triploid fish versus diploid fish at production‐site level, and a tendency of increased odds (3.4) of ISA in triploid fish at individual cage level at sited with primary outbreaks. At some sites, ISA outbreaks were only diagnosed in cages with triploid fish and not in cages with diploid fish. Primary ISA outbreaks are the source for further spread of the disease, and it is noteworthy that in an experimental trial we found significantly more viral RNA in non‐ISA‐vaccinated triploid than in non‐ISA‐vaccinated diploid fish at the peak of the infection. Interestingly, the notable differences of susceptibility to ISA for non‐ISA vaccinated diploid and triploid fish observed in field were not repeated experimentally. The possible increased risk of ISA should be considered when evaluating the costs and benefits of triploid salmon in farming. It is recommended to keep triploid and diploid fish in biosecure separated sites, or that triploid fish are not farmed at all.

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“…Subclinically ISAV-infected feral Atlantic salmon, brown trout and sea trout (S. trutta) and escaped, farmed rainbow trout (Oncorhynchus mykiss) have been identified by RT-PCR (Raynard et al, 2001;Plarre et al, 2005). Waterborne transmission in juvenile rainbow trout, including high mortalities in genetically susceptible fish strains, have been found in some experimental set-ups (Biacchesi et al, 2007), while serial passage of a virulent strain of ISAV in larger rainbow trout did not produce clinical disease (Olsen et al, 2012). Positive RT-PCR for ISAV has also been reported in wild Atlantic cod (Gadus morhua), alewife (Alosa pseudoharengus) and pollock (Pollachius virens) (MacLean et al, 2003;Rolland, 2004), but contamination by virus present in the surrounding water cannot be excluded as the fish were collected close to cages with Atlantic salmon exhibiting ISA.…”

Section: Species Rangementioning

confidence: 99%

Scientific Opinion on infectious salmon anaemia (ISA)

Authié¹,

Berg²,

Bøtner³

et al. 2012

EFSA Journal

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Atlantic salmon is the only species in which the disease infectious salmon anaemia (ISA) has been observed naturally. Initial reports of findings of infectious salmon anaemia virus (ISAV) before 2002, did not distinguish between non virulent HPR0 and virulent HPRΔ viruses, thus making interpretation of older findings difficult in the light of current knowledge. Following a request from the European Commission, EFSA was asked to deliver a scientific opinion on the relationship between HPR0 and HPRΔ, the risk of HPRΔ ISAV emerging from HPR0 ISAV, and possible risk factors for such an emergence. HPR0 ISAV does not cause clinical disease in Atlantic salmon; however, it causes a transient subclinical infection and replicates mainly in gills. There is no evidence for HPR0 ISAV leading to natural infection and replication in fish species other than Atlantic salmon. Virulent ISAV have deletions in the HPR region of the HE gene and they have either an insertion or the Q266L mutation in the F gene. The most plausible hypothesis is that virulent ISAV (HPRΔ) is derived from HPR0 ISAV. This is further supported by the close association between the genetic relatedness and spatio-temporal distances of virus strains in solitary outbreaks. Epidemiological and historical data from solitary disease outbreaks indicates that the risk of HPRΔ ISAV emerging from HPR0 is low, but not negligible. The risk factors for HPRΔ emergence from HPR0 are unknown. Nevertheless, any factor that affects virus replication or host susceptibility could possibly influence the risk of emergence. More research is needed on the drivers for transition from HPR0 to HPRΔ and factors affecting host susceptibility and thereby emergence of clinical disease. A quantitative assessment of the different evolutionary forces for ISA would be useful, as well as the prevalence of ISAV HPR0 in farmed and wild Atlantic salmon

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Multiple passage of infectious salmon anaemia virus in rainbow trout, Oncorhynchus mykiss (Walbaum), did not induce increased virus load

Cited by 5 publications

References 45 publications

Salmon Erythrocytes Sequester Active Virus Particles in Infectious Salmon Anaemia

Salmon Erythrocytes Sequester Active Virus Particles in Infectious Salmon Anaemia

Triploid Atlantic salmon (Salmo salar) may have increased risk of primary field outbreaks of infectious salmon anaemia

Scientific Opinion on infectious salmon anaemia (ISA)

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