Heart and Skeletal Muscle Inflammation of Farmed Salmon Is Associated with Infection with a Novel Reovirus

Abstract

Atlantic salmon (Salmo salar L.) mariculture has been associated with epidemics of infectious diseases that threaten not only local production, but also wild fish coming into close proximity to marine pens and fish escaping from them. Heart and skeletal muscle inflammation (HSMI) is a frequently fatal disease of farmed Atlantic salmon. First recognized in one farm in Norway in 1999[1], HSMI was subsequently implicated in outbreaks in other farms in Norway and the United Kingdom[2]. Although pathology and disease transmission studies indicated an infectious basis, efforts to identify an agent were unsuccessful. Here we provide evidence that HSMI is associated with infection with piscine reovirus (PRV). PRV is a novel reovirus identified by unbiased high throughput DNA sequencing and a bioinformatics program focused on nucleotide frequency as well as sequence alignment and motif analyses. Formal implication of PRV in HSMI will require isolation in cell culture and fulfillment of Koch's postulates, or prevention or modification of disease through use of specific drugs or vaccines. Nonetheless, as our data indicate that a causal relationship is plausible, measures must be taken to control PRV not only because it threatens domestic salmon production but also due to the potential for transmission to wild salmon populations.

Diseases of farmed Atlantic salmon Salmo salar associated with infections by the microsporidian Paranucleospora theridion

“…These diseases were selected due to the large discrepancies between the observed pathology and mortality in marine already recognised that several pathogens are associated with gill diseases (A. Nylund et al 1998, 2009a,b, Kvellestad et al 2003, Draghi et al 2004, Fridell et al 2004, Todal et al 2004, Callahan et al 2005, Young et al 2007, Steinum et al 2008, and it has also proven difficult to perform challenge experiments with most of these agents. The other 3 diseases, PD, HSMI and CMS, are all associated with the presence of viruses , 2006, Vågenes et al 1999, Nylund 2001, Kongtorp et al 2004a, Bruno & Noguera 2009, Fritsvold et al 2009, Palacios et al 2010, but it is difficult, in challenge experiments, to reproduce both the mortality and all the pathological changes observed during outbreaks in farms. In the present study we present the pathogens that are associated with these diseases in Norwegian culture of salmonids with a special emphasis on the possible importance of Paranucleospora theridion.…”

“…Several studies have suggested that HSMI and CMS are associated with viruses , 2006, Vågenes et al 1999, Nylund 2001, Kongtorp et al 2004a, Bruno & Noguera 2009, Fritsvold et al 2009, Palacios et al 2010. However, using homogenates containing these viruses in challenge experiments will not reproduce all the signs of these diseases and the mortality observed in field outbreaks (A. Nylund pers.…”

Occurrence of salmonid alphavirus (SAV) and piscine orthoreovirus (PRV) infections in wild sea trout Salmo trutta in Norway

“…This assay detects both SAV2 and SAV3, the subtypes occurring in Norway (Hjortaas et al 2013). The PRV assay used was as described by Glover et al (2013), based on sequences published by Palacios et al (2010). Samples with a cycle-threshold (C t ) value below 37.0 were considered positive.…”

Population biology of infectious diseases shared by wild and farmed fish

“…Parasite dispersal connects the population dynamics of disease among farms within a region as well as between farmed salmon and the wild salmon populations that migrate through the aquaculture regions as juveniles and as adults. flammation disease; Palacios et al 2010) are considered exotic to the North Pacific Ocean, but PCR tests of farmed and wild salmon have indicated that strains of these ancestrally Norwegian viruses may now be present in both wild and farmed salmon in British Columbia (Kibenge et al 2013(Kibenge et al , 2016Marty et al 2015). These examples underscore the need for continuing and increasing biosecurity practices that focus on the trade and movement of seafood products -including aquaculture products, feed, eggs, and broodstock -at regional and global scales.…”