Presence and genetic variability of Piscine orthoreovirus genotype 1 (PRV‐1) in wild salmonids in Northern Europe and North Atlantic Ocean

Abstract

Piscine orthoreovirus genotype 1 (PRV‐1) is widespread in farmed Atlantic salmon (Salmo salar L.) populations in northern Europe, Canada and Chile. PRV‐1 occurs in wild fish in Norway and Canada; however, little information of its geographical distribution in wild populations is currently available, and the effect of PRV‐1 infection in wild populations is currently unknown. In this study, we present the findings of a survey conducted on 1,130 wild salmonids sampled in Denmark, Sweden, Ireland, Faroe Islands, France, Belgium and Greenland between 2008 and 2017. PRV‐1 is reported for the first time in wild salmonids in Denmark, Sweden, Faroe Island and Ireland. The annual PRV‐1 prevalence ranged from 0% in France, Belgium and Greenland to 43% in Faroe Islands. In total, 66 samples tested positive for PRV‐1, including Atlantic salmon broodfish returning to spawn and Atlantic salmon collected at the feeding ground north of Faroe Islands. The phylogenetic analysis of S1 sequences of the PRV‐1 isolates obtained in this survey did not show systematic geographical distribution. This study sheds light on the spread and genetic diversity of the virus identified in populations of free‐living fish and provides rationale for screening wild broodfish used in restocking programmes.

A molecular assessment of infectious agents carried by Atlantic salmon at sea and in three eastern Canadian rivers, including aquaculture escapees and North American and European origin wild stocks

“…First, we identified both North American and European origin fish in marine waters off the coast of Greenland, providing further evidence to support this feeding area as a multi-continental melting pot (Hansen and Quinn 1998;Sheehan et al 2012;Chaput et al 2019). The similar infectious agent composition between North American and European origin hosts sampled in Greenland, and the finding of virtually identical PRV-1 genome sequences in fish of different continental origins supports the hypothesis of inter-continental transmission of pathogens in North Atlantic feeding areas where stocks mix (Madhun et al 2018;Vendramin et al 2019). Second, the high degree of similarity of the PRV-1 genome sequenced from two independent aquaculture escapees in eastern Canada suggests a common source or transmission of PRV-1 within aquaculture facilities that was distinct from the two wild fish sequenced in this study.…”

“…FACETS | 2020 | 5: 234-263 | DOI: 10.1139/facets-2019-0048 249 facetsjournal.com the hypothesis that ocean feeding grounds, where fish from different continents converge, provide a natural pathway of agent transmission between Europe and North America (Gagné and LeBlanc 2018;Madhun et al 2018;Vendramin et al 2019). We found high homology between sequences of PRV-1 isolated from two escaped farm salmon in eastern Canada in 2017, one collected from the Magaguadavic River in New Brunswick (this study) and the other recovered in Shelburne Harbour, Nova Scotia (Kibenge et al 2017;F.…”

“…Substantial mixing of stocks occurs in the Labrador Sea near Greenland (Chaput et al 2018), including both North American and European origin fish (Reddin and Friedland 1999;Sheehan et al 2012). This mixing not only provides an opportunity for infectious agents to spread among individuals, but also geographical areas since salmon will eventually migrate back to natal freshwater systems to spawn (Madhun et al 2018;Vendramin et al 2019). Introduction of emerging pathogens or pathogen strains through intercontinental exchange may pose new risks to otherwise threatened populations in a way that is not easily controlled by anthropogenic activities.…”

Piscine orthoreovirus: Biology and distribution in farmed and wild fish

“…Consistent among all PRV‐1 phylogenetic studies to date is that there appears to be relatively high (>99%) genome homology between sequences obtained in the Eastern Pacific compared to the North Atlantic (as low as ~97.5% homology) and that the Pacific isolates ordinate with one of the two major subgroups (PRV‐1a) that co‐occur with PRV‐1b in Norway and Chile (Figure 2). Isolates from multiple PRV genogroups (specifically PRV‐1 and PRV‐3) have been naturally detected within a single individual host (Cartagena et al., 2018; Cartagena, Jiménez, & Spencer, 2020), providing the potential for segment reassortment between genogroups and potentially sub‐genogroups in those regions such as Norway and Denmark where multiple variants have been identified to temporally coexist (Vendramin, Cuenca, et al, 2019). It is believed that such reassortment has historically occurred at least within subgroups of PRV‐1 (Dhamotharan et al., 2019; Siah et al, in press ).…”

“…PRV‐1 was first identified in Norway (Palacios et al., 2010) and has since been ubiquitously detected in that country (Løvoll et al., 2012; Wiik‐Nielsen, Alarcón, Jensen, Haugland, & Mikalsen, 2016). PRV‐1 is also commonly detected in other North Atlantic countries including Canada, the United Kingdom, Ireland, Iceland, Germany, Denmark, Faroe Islands and France with an additional single detection from Sweden (Adamek et al., 2018; Biering & Garseth, 2012; Ferguson et al., 2020; Gunnarsdóttir, Sigurðardóttir, Bragason, & Guðmundsdótti, 2018; Labrut, Bigarré, Boitard, & Jamin, 2018; Vendramin, 2019; Vendramin, Cuenca, et al, 2019). In the Pacific region, PRV‐1 has been detected along the west coast of the United States and Canada as well as in Chile (Godoy et al., 2016; Marty et al., 2015; Purcell et al., 2018).…”