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Phylogenetic evidence of long distance dispersal and transmission of piscine reovirus (PRV) between farmed and wild Atlantic salmon.

ABSTRACT: The extent and effect of disease interaction and pathogen exchange between wild and farmed fish populations is an ongoing debate and an area of research that is difficult to explore. The objective of this study was to investigate pathogen transmission between farmed and wild Atlantic salmon (Salmo salar L.) populations in Norway by means of molecular epidemiology. Piscine reovirus (PRV) was selected as the model organism as it is widely distributed in both farmed and wild Atlantic salmon in Norway, and because infection not necessarily will lead to mortality through development of disease. A matrix comprised of PRV protein coding sequences S1, S2 and S4 from wild, hatchery-reared and farmed Atlantic salmon in addition to one sea-trout (Salmo trutta L.) was examined. Phylogenetic analyses based on maximum likelihood and Bayesian inference indicate long distance transport of PRV and exchange of virus between populations. The results are discussed in the context of Atlantic salmon ecology and the structure of the Norwegian salmon industry. We conclude that the lack of a geographical pattern in the phylogenetic trees is caused by extensive exchange of PRV. In addition, the detailed topography of the trees indicates long distance transportation of PRV. Through its size, structure and infection status, the Atlantic salmon farming industry has the capacity to play a central role in both long distance transportation and transmission of pathogens. Despite extensive migration, wild salmon probably play a minor role as they are fewer in numbers, appear at lower densities and are less likely to be infected. An open question is the relationship between the PRV sequences found in marine fish and those originating from salmon.

SUBMITTER: Garseth AH

PROVIDER: S-EPMC3859594 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Piscine orthoreovirus (PRV) is an emergent virus in salmon aquaculture belonging to the family Reoviridae. PRV is associated with a growing list of pathological conditions including heart and skeletal inflammation (HSMI) of farmed Atlantic salmon. Despite widespread PRV infection in commercially farmed Atlantic salmon, information on PRV prevalence and on the genetic sequence variation of PRV in Atlantic salmon on the north Pacific Coast is limited. METHODS:Feral Atlantic salmon caught in Washington State and British Columbia following a large containment failure at a farm in northern Puget Sound were sampled. Fish tissues were tested for PRV by RT-qPCR assay for segment L1 and conventional RT-PCR for PRV segment S1. The PCR products were sequenced and their relationship to PRV strains in GenBank was determined using phylogenetic analysis and nucleotide and amino acid homology comparisons. RESULTS:Following the escape of 253,000 Atlantic salmon from a salmon farm in Washington State, USA, 72/73 tissue samples from 27 Atlantic salmon captured shortly after the escape tested PRV-positive. We estimate PRV-prevalence in the source farm population at 95% or greater. The PRV found in the fish was identified as PRV sub-genotype Ia and very similar to PRV from farmed Atlantic salmon in Iceland. This correlates with the source of the fish in the farm. Eggs of infected fish were positive for PRV indicating the possibility of vertical transfer and spread with fish egg transports. CONCLUSIONS:PRV prevalence was close to 100% in farmed Atlantic salmon that were caught in Washington State and British Columbia following a large containment failure at a farm in northern Puget Sound. The PRV strains present in the escaped Atlantic salmon were very similar to the PRV strain reported in farmed Atlantic salmon from the source hatchery in Iceland that was used to stock commercial aquaculture sites in Washington State. This study emphasizes the need to screen Atlantic salmon broodstock for PRV, particularly where used to supply eggs to the global Atlantic salmon farming industry thereby improving our understanding of PRV epidemiology.

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Phylogenetic evidence of long distance dispersal and transmission of piscine reovirus (PRV) between farmed and wild Atlantic salmon.

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