Very few virus infections found in migrating postsmolts from the Trondheim Fjord
Commissioned by the Norwegian Food Safety Authority, the Institute of Marine Research has studied the occurrence of several potential disease-causing viruses that are common in salmon farming in imigrating postsmolts from Trondheim fjord in 2016. The postsmolts were caught in the mouth of the fjord, which is a national salmon fjord without fish farming activity, and therefore it is unlikely that this fish is exposed to infections from salmon farming. The incidence of SAV, PRV1, ILAV and PMCV infections was tested using the real-time RT-PCR method. SAV, PRV1, ILAV were not detected in any of the postsmolts. Low concentration of PMCV was detected in a single fish. The results show that the occurrence of these viruses is very low in wild salmon postsmolts in this area of the fjord.publishedVersio

Karlsbakk, Egil

Karlsen, Ørjan

Madhun, Abdullah Sami

English

Brage IMR

ANNUAL REPORT ON HEALTH MONITORING OFWILD ANADROMOUS SALMONIDS IN NORWAY 2018Screening of migrating Atlantic salmon (Salmo salar) postsmolts from theTrondheim fjord for viral infectionsAbdullah Sami Madhun, Ørjan Karlsen og Egil Karlsbakk (Havforskningsinstituttet) Bengt Finstad (Norwegian Institute for Nature Research)RAPPORT FRAHAVFORSKNINGENNR. 2019-28Rapportserie:Rapport fra Havforskningen ISSN:1893-4536År - Nr.:2019-28Dato:21.06.2019Forfatter(e):Abdullah Sami Madhun, Ørjan Karlsen og Egil Karlsbakk(Havforskningsinstituttet) Bengt Finstad (Norwegian Institute for Nature Research)Faggruppeleder(e): Bjørn Olav Kvamme (Sykdom og smittespredning)Godkjent av: Forskningsdirektør(er): Geir Lasse Taranger Programleder(e):Terje SvåsandDistribusjon:ÅpenProsjektnr:14896-03Oppdragsgiver(e):Norwegian Food Safety AuthorityProgram:AkvakulturFaggruppe(r):Sykdom og smittespredningAntall sider:9Tittel (norsk og engelsk):Annual report on health monitoring of wild anadromous salmonids in Norway 2018Undertittel (norsk og engelsk):Screening of migrating Atlantic salmon (Salmo salar) postsmolts from the Trondheim fjord for viral infectionsSamarbeid medSammendrag (norsk):Very few virus infections found in migrating postsmolts from the Trondheim FjordCommissioned by the Norwegian Food Safety Authority, the Institute of Marine Research has studied the occurrence ofseveral potential disease-causing viruses that are common in salmon farming in imigrating postsmolts from Trondheimfjord in 2016. The postsmolts were caught in the mouth of the fjord, which is a national salmon fjord without fish farmingactivity, and therefore it is unlikely that this fish is exposed to infections from salmon farming. The incidence of SAV,PRV1, ILAV and PMCV infections was tested using the real-time RT-PCR method. SAV, PRV1, ILAV were notdetected in any of the postsmolts. Low concentration of PMCV was detected in a single fish. The results show that theoccurrence of these viruses is very low in wild salmon postsmolts in this area of the fjord.Sammendrag (engelsk):Svært få funn av virus i utvandrende postsmolt fra TrondheimsfjordenPå oppdrag fra Mattilsynet har Havforskningsinstituttet undersøkt forekomsten avflere mulige sykdomsfremkallende virus som er prevalent i oppdrett i utvandrende postsmolt fraTrondheimsfjorden i 2016. Postsmolten ble fanget i munning til fjorden, som er en nasjonal laksefjord utenoppdrettsaktivit, og det er derfor lite sannsynlig at denne smolten er utsett for smitte fra oppdrett. Forekomsten av SAV-,PRV1-, ILAV- og PMCV-infeksjoner ble testet ved å bruke sanntids RT-PCR metoden. SAV, PRV1 og ILAV ble ikkepåvist i postsmolten. Lav konsentrasjon av PMCV ble detektert i en fisk. Resultatene tyder på at infeksjoner med dissevirusene er uvanlige i vill laks postsmolt  i dette fjordområdet.  Innhold1.1 Introduction 61.2 Aim 71.3 Materials and methods 71.4 Results 81.5 Discussion and conclusion 81.6 References 8 1.1 - IntroductionViral diseases are one of the major challenges facing Atlantic salmon farming in Norway that often lead to substantialeconomic losses (Table 1). The most common viral diseases in salmon farming the last five years are; pancreas disease(PD), caused by salmonid alphavirus (SAV), heart and skeletal muscle inflammation (HSMI), caused by a piscineorthoreovirus 1 (PRV1), cardiomyopathy syndrome (CMS) caused by piscine myocarditis virus (PMCV) and infectioussalmon anaemia (ISA)  caused by ISA virus (ISAV).Table 1: The number of registered viral disease outbreaks in fish farming in the last 5 years [1]. 2014 2015 2016 2017 2018PD 142 137 138 176 163HSMB 181 135* 101* 93* 104*CMS 107 105* 90* 100* 101*ISA 10 15 12 14 13* Underreported. Disease outbreaks in salmon farms may lead to increased infection pressure on neighbouring farms and local wild fishpopulations. There is increasing public concern of this negatively impacting wild salmonids in Norway. However, thereare limited data on the prevalence of pathogens in wild salmonid populations [2]. It is difficult to quantify diseaseincidence and its impact in wild fish since sick individuals may be less catchable or may disappear unnoticed (e.g. dueto predation). Therefore, it is challenging to evaluate the impact of disease in wild stocks since we normally are onlyable to collect infected but non-diseased fish such as individuals that has recently acquired or has survived an infection(carriers).Pathogens that cause disease in farmed salmon can also infect wild salmon. The effect of fish farming on the infectionstatus of wild salmon stocks may be evaluated by comparing pathogen prevalence in wild fish populations capturedfrom coastal areas that have different fish farming intensities and disease outbreak profile.Wild salmon may be infected by viruses prevalent in salmon farming; in rivers as parr by virus-infected farmedescapees and spawning wild salmon or from salmon farms in the fjord when migrating as postsmolts or returning asadults. Therefore, infection status in migrating postsmolts may represent a direct indicator of infection pressure fromsalmon farming during their migration routes. However, it is important to establish “background” prevalence of viralinfections in migrating wild postsmolts before being eventually exposed to infection from fish farming. The Trondheimfjord is a national salmon fjord with no salmon sea farms (Fig. 1). Migrating postsmolts originated from rivers in the fjordmay be used to study the occurrence of viral infections in wild fish exposed to no or limited infections from fish farming.Annual report on health monitoring of wild anadromous salmonids in Norway 20181.1 - Introduction5/91.2 - AimThe aim of the current study was to investigate the occurrence of SAV, PRV1, PMCV and ISAV infections in migratingwild Atlantic salmon postsmolts originating from rivers flowing into the Trondheim fjord.1.3 - Materials and methodsMigrating postsmolts (N=200) were captured in the outer parts of the Trondheim fjord by trawling in May-June (Fig. 1),as part of the national salmon lice monitoring program [3]. The weight and length of the fish were determined and thepostsmolts were then frozen (-20 C) as soon as possible after capture. At autopsy, tissues from the gills, head kidneyand heart were taken out from the fish while still frozen and were sent on dry ice to an accredited commercial laboratoryfor RNA extraction and virus testing (Pharmaq Analytiq AS). Analyses for SAV, PRV1, PMCV and ISAV viruses (fordetection viral RNA) were performed on a mixed tissue samples by real-time PCR assays. Ct-values less than or equal40 were considered positive.Fig. 1: A map showing the trawling area (blue) in the outer part of the Trondheim fjord and salmon farms (red triangles). oAnnual report on health monitoring of wild anadromous salmonids in Norway 20181.2 - Aim6/91.4 - ResultsVirus infections in wild postsmolts from the Trondheim fjord.SAV, PRV1 and ISAV were not detected in any of the tissues from the tested postsmolts. PMCV was detected in onesingle postsmolt (Ct-value 37).1.5 - Discussion and conclusionExcept one PMCV-positive fish, none of the migrating postsmolts were infected with the tested viruses. The Trondheimfjord is a national salmon fjord with no fish farming activities (Fig. 1). Therefore, the postsmolts which were captured inthe outer part (mouth) of the fjord were likely not exposed to viruses prevalent in salmon sea farms. The prevalence ofvirus infections in migrating postsmolt from the fjord likely reflects the infection status across the rivers of origin.A single postsmolt was PMCV-positive showing a virus prevalence of 0.5 %. It is most likely that the PMCV-positivepostsmolt in the current study was infected in river of origin. Indeed, a high prevalence (up to 19 %) of PMCV infectionwas found in wild parr from a river in western Norway [4]. Studies of escaped farmed salmon entering rivers in theHardanger fjord showed that most of the escapees often are infected with one or more viruses, including PMCV [5, 6].Therefore,escaped farmed salmon may act as pathogen vectors that may transfer infections to wild salmon populationsin rivers. However, very low numbers of escaped farmed salmon were registered in the rivers located in the Trondheimfjord [7]. On the other hand, a low natural occurrence of PMCV infection in wild salmon populations in rivers can beexcluded.We previously reported that the prevalence of PRV1 was low (2-6%) in migrating postsmolts from western Norway, butstill significantly higher compared to the current study [4]. The postsmolts from western Norway were captured in theouter part of the fjords after passing through areas with fish farming and therefore they may be contracted the viruseither in their migration routes or in the rivers of origin.The absence of SAV infection in the postsmolts is in accordance with our previous findings, suggesting that infectionwith this virus seems exceedingly rare in all life stages of salmon in Norway [4].Avirulent ISAV infections are prevalent in salmon farming [8, 9] and may occur in wild adult salmon [ref. 10]. However,so far, we did not detect the virus in the migrating postsmolts [4].The results from the current report showed very low prevalence of viral infections in migrating postsmolts originatedfrom rivers located in the Trondheim fjord, suggesting that background natural occurrence of these viruses is very low inwild postsmolts. Time series of samples of migrating postsmolts from areas with different salmon farming intensities areneeded to better evaluate the effect of infection pressure from aquaculture on the virus prevalence in wild salmonpopulations. The studies on migrating postsmolts will continue in the coming years in different fjord systems from southto north, covering larger parts of the Norwegian coastline.1.6 - References1- Hjeltnes, B., et al., Fish health report 2018 (in Norwegian). 2019, Norwegian Veterinary Institute: NorwegianVeterinary Institute. p. 132.2- Taranger, G.L., et al., Risk assessment of the environmental impact of Norwegian Atlantic salmon farming. ICESJournal of Marine Science, 2015. 72(3): p. 997-1021.3- Nilsen, R., et al., Lakselusinfestasjon på vill laksefisk langs norskekysten i 2016; med vekt på modellbasert varslingog tilstandsbekreftelse. 2017, Havforskningsinstituttet: Havforskningsinstituttet.4- Grefsrud, E.S., et al., Risk assessment of Norwegian fish farming (in Norwegian). 2018, Institute of MarineResearch: Institute of Marine Research. p. 181.Annual report on health monitoring of wild anadromous salmonids in Norway 20181.4 - Results7/95- Madhun, A.S., et al., Potential disease interaction reinforced: double-virus-infected escaped farmed Atlantic salmon,Salmo salar L., recaptured in a nearby river. Journal of Fish Diseases, 2015. 38(2): p. 209-19.6- Madhun, A.S., et al., The ecological profile of Atlantic salmon escapees entering a river throughout an entire season:diverse in escape history and genetic background, but frequently virus-infected. Ices Journal of Marine Science, 2017.74(5): p. 1371-1381.7- Anonymous, Rømt oppdrettslaks i vassdrag. Rapport fra det nasjonale overvåkingsprogrammet 2017, in Fisken oghavet. 2018, Havforskningsinstituttet. p. 69.8- Christiansen, D.H., et al., A low-pathogenic variant of infectious salmon anemia virus (ISAV-HPR0) is highlyprevalent and causes a non-clinical transient infection in farmed Atlantic salmon (Salmo salar L.) in the Faroe Islands.Journal of General Virology, 2011. 92: p. 909-918.9- Lyngstad, T.M., et al., Low virulent infectious salmon anaemia virus (ISAV-HPR0) is prevalent and geographicallystructured in Norwegian salmon farming. Diseases of Aquatic Organisms, 2012. 101(3): p. 197-206.10- Madhun, A.S., et al., Prevalence and genotypes of infectious salmon anaemia virus (ISAV) in returning wild Atlanticsalmon (Salmo salar L.) in northern Norway. Journal of Fish Diseases, 2019: (in press).Annual report on health monitoring of wild anadromous salmonids in Norway 20181.4 - Results8/9HAVFORSKNINGSINSTITUTTETPostboks 1870 Nordnes 5817 Bergen E-post: post@hi.no www.hi.no 

Annual report on health monitoring of wild anadromous salmonids in Norway 2018 - Screening of migrating Atlantic salmon (Salmo salar) postsmolts from the Trondheim fjord for viral infections

Very few virus infections found in migrating postsmolts from the Trondheim Fjord
Commissioned by the Norwegian Food Safety Authority, the Institute of Marine Research has studied the occurrence of several potential disease-causing viruses that are common in salmon farming in imigrating postsmolts from Trondheim fjord in 2016. The postsmolts were caught in the mouth of the fjord, which is a national salmon fjord without fish farming activity, and therefore it is unlikely that this fish is exposed to infections from salmon farming. The incidence of SAV, PRV1, ILAV and PMCV infections was tested using the real-time RT-PCR method. SAV, PRV1, ILAV were not detected in any of the postsmolts. Low concentration of PMCV was detected in a single fish. The results show that the occurrence of these viruses is very low in wild salmon postsmolts in this area of the fjord

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Annual report on health monitoring of wild anadromous salmonids in Norway 2018 - Screening of migrating Atlantic salmon (Salmo salar) postsmolts from the Trondheim fjord for viral infections

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