Infection experiments with novel Piscine orthoreovirus from rainbow trout (Oncorhynchus mykiss) in salmonids

Heart and skeletal muscle inflammation (HSMI) caused by piscine orthoreovirus (PRV) and pancreas disease (PD) caused by salmonid alphavirus (SAV) are among the most prevalent viral diseases of Atlantic salmon farmed in Norway. There are limited data about the impact of disease in farmed salmon on wild salmon populations. Therefore, the prevalence of PRV and SAV in returning salmon caught in six sea sites was determined using real-time RT-PCR analyses. Of 419 salmon tested, 15.8% tested positive for PRV, while none were positive for SAV. However, scale reading revealed that 10% of the salmon had escaped from farms. The prevalence of PRV in wild salmon (8%) was significantly lower than in farm escapees (86%), and increased with fish length (proxy for age). Sequencing of the S1 gene of PRV from 39 infected fish revealed a mix of genotypes. The observed increase in PRV prevalence with fish age and the lack of phylogeographic structure of the virus could be explained by virus transmission in the feeding areas. Our results highlight the need for studies about the prevalence of PRV and other pathogens in Atlantic salmon in its oceanic phase. Disease outbreaks in salmon farms may lead to increased infection and disease risks at neighbouring farms and in wild fish populations, and there is an increasing public concern of disease impacting wild salmon populations in Norway (Sv asand et al., 2017). Data are collected annually on the frequency and geographical distribution of disease outbreaks in fish farms (Hjeltnes et al., 2017). Correlating such data from regions differing in farming intensities and disease profiles with pathogen prevalence in local wild salmon populations would thus help to address this concern. However, pathogen prevalence data alone as an indicator of infection pressure have ----------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Section: Methodsmentioning

confidence: 99%

Prevalence of piscine orthoreovirus and salmonid alphavirus in sea‐caught returning adult Atlantic salmon (Salmo salar L.) in northern Norway

Madhun

Isachsen

Omdal

et al. 2018

“…Coho salmon (O. kisutch Walbaum) in Japan (Takano et al, 2016), and PRV-3 has been shown to induce heart pathology and anaemia in farmed rainbow trout (O. mykiss Walbaum) (Hauge et al, 2017;Olsen, Hjortaas, Tengs, Hellberg, & Johansen, 2015). PRV-1 is considered to infect almost all farmed Atlantic salmon during the sea phase in Norway Løvoll et al, 2012).…”

Section: Prv-2 Causes Erythrocytic Inclusion Body Syndrome (Eibs) In mentioning

confidence: 99%

“…Currently, three PRV genotypes have been described. PRV‐1 is the causative agent of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon in Norway (Wessel et al, ), PRV‐2 causes erythrocytic inclusion body syndrome (EIBS) in farmed Coho salmon ( O. kisutch Walbaum) in Japan (Takano et al, ), and PRV‐3 has been shown to induce heart pathology and anaemia in farmed rainbow trout ( O. mykiss Walbaum) (Hauge et al, ; Olsen, Hjortaas, Tengs, Hellberg, & Johansen, ). PRV‐1 is considered to infect almost all farmed Atlantic salmon during the sea phase in Norway (Haatveit et al, ; Løvoll et al, ).…”

Section: Introductionmentioning

confidence: 99%

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

Vendramin

Cuenca

Sørensen

et al. 2019

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.

“…Experimental infection studies have strengthened the association between PRV‐3 and the disease signs seen in rainbow trout (Hauge et al, ). The infection transmitted to all of rainbow trout cohabitants that also developed disease symptoms.…”

Section: Introductionmentioning

confidence: 98%

Piscine orthoreovirus‐3 is prevalent in wild seatrout (Salmo trutta L.) in Norway

Garseth

Moldal

Gåsnes

et al. 2019

In 2017, a PCR‐based survey for Piscine orthoreovirus‐3 (PRV‐3) was conducted in wild anadromous and non‐anadromous salmonids in Norway. In seatrout (anadromous Salmo trutta L.), the virus was present in 16.6% of the fish and in 15 of 21 investigated rivers. Four of 221 (1.8%) Atlantic salmon (Salmo salar L.) from three of 15 rivers were also PCR‐positive, with Ct‐values indicating low amounts of viral RNA. All anadromous Arctic char (Salvelinus alpinus L.) were PCR‐negative. Neither non‐anadromous trout (brown trout) nor landlocked salmon were PRV‐3 positive. Altogether, these findings suggest that in Norway PRV‐3 is more prevalent in the marine environment. In contrast, PRV‐3 is present in areas with intensive inland farming in continental Europe. PRV‐3 genome sequences from Norwegian seatrout grouped together with sequences from rainbow trout (Oncorhynchus mykiss Walbaum) in Norway and Coho salmon (Oncorhynchus kisutch Walbaum) in Chile. At present, the origin of the virus remains unknown. Nevertheless, the study highlights the value of safeguarding native fish by upholding natural and artificial barriers that hinder introduction and spread, on a local or national scale, of alien fish species and their pathogens. Accordingly, further investigations of freshwater reservoirs and interactions with farmed salmonids are warranted.