Concentration and detection of salmonid alphavirus in seawater during a post-smolt salmon (Salmo salar) cohabitant challenge

Abstract

Currently, the prevalence of salmonid alphavirus (SAV) in Norwegian Atlantic salmon farms is largely surveyed via sacrificing fish and sampling of organ tissue on a monthly basis. However, a more cost-efficient, straightforward, rapid, reliable, reproducible and animal welfare friendly method based on the detection of SAV in water could be considered as an alternative method. In the present study, such a method was developed and optimized through a 6 wk cohabitant challenge trial, using post-smolt Atlantic salmon Salmo salar L challenged with high or low doses of SAV subtype 3 (SAV3). Tank water and tissue samples from cohabitant fish were collected at 16 time points. SAV3 was concentrated from the water by filtration, using either electronegative or electropositive membrane filters, which were subsequently rinsed with one of 4 different buffer solutions. SAV3 was detected first in tank water (7 d post-challenge, DPC), and later in cohabitant fish organ tissue samples (12 DPC). The electronegative filter (MF-Millipore™) and rinsing with NucliSENS® easyMAG® Lysis Buffer presented the best SAV3 recovery. A significant positive correlation was found between SAV3 in the tank water concentrates and the mid-kidney samples. Based on these results, detection of SAV3 in filtrated seawater is believed to have the potential to serve as an alternative method for surveillance of SAV in Atlantic salmon farms.

Short communication: Evaluation of charged membrane filters and buffers for concentration and recovery of infectious salmon anaemia virus in seawater

“…The principle of eDNA detection, which involves the detection of genetic material from various organisms in water samples, in order to identify the presence of the actual organisms in the water bodies (lakes, rivers), has also been applied for surveillance purposes of disease agents in wild aquatic animals in freshwater, like crayfish plague ( Aphanomyces astaci ) in Noble crayfish ( Astacus astacus ) [ 19 ] and Gyrodactylus salaris in Atlantic salmon ( Salmo salar ) [ 20 ]. Moreover, we have promising results regarding concentration and detection of Salmonid alphavirus from seawater both in laboratory experiments [ 21 ] and infection trials with Atlantic salmon [ 22 ].…”

A de novo Full-Length mRNA Transcriptome Generated From Hybrid-Corrected PacBio Long-Reads Improves the Transcript Annotation and Identifies Thousands of Novel Splice Variants in Atlantic Salmon

“…Two of the head-kidney samples included in the study (SAV_Control and SAV_challenge, Table 1) were from one healthy control fish and one fish challenged with Salmonid Alphavirus, respectively. The challenge trial was carried out at the Industrial and Aquatic Laboratory (ILAB, Bergen High Technology Centre, Bergen, Norway) in February/March of 2018 (Bernhardt et al, 2021). Post-smolt fish from the breed SF Optimal (Stofnfiskur Iceland) were challenged by cohabitation in saltwater with salmon shedders (carrier fish) injected with salmonid alphavirus subtype 3 (SAV3) from Norway (Taksdal et al, 2015).…”

“…Shortly, fish were anesthetized by an overdose of MS-222 (tricaine 123 methanesulfonate, 0.1 g/L) prior to sampling and killed by a blow to the head. The tissue samples were immediately collected, frozen in liquid hydrogen and stored at −80 • C. All fish handling procedures complied with the guidelines of the EU-legislation (2010/63/EU), as well as with The smoltification samples 1 are from a study of Shwe et al (2020) while the challenge samples 2 are from Bernhardt et al (2021).…”

“…We have a particular interest in the study of expression changes and regulation of gene expression during smoltification and sea-water transfer as well as expression changes and gene regulation in response to infectious diseases (Woldemariam et al, 2019(Woldemariam et al, , 2020Shwe et al, 2020). Two of the samples included in this study were therefore selected from a challenge study to reveal the full-length sequences of mRNAs expressed in head-kidney when infected with salmonid alpha virus (SAV) (McLoughlin and Graham, 2007;Andreassen et al, 2017;Bernhardt et al, 2021). Samples from head-kidney were chosen, as this is one of the main immune organ in fish and frequently used in fish immunological studies of gene expression (Bjørgen and Koppang, 2021).…”

Infectious Salmon Anemia Virus Shedding from Infected Atlantic Salmon (Salmo salar L.)—Application of a Droplet Digital PCR Assay for Virus Quantification in Seawater

“…Recently, we have developed a method for detection of Salmonid alphavirus (SAV) in seawater for surveillance purposes [ 19 , 20 ]. In order to also implement this methodology for ISAV, in vitro experiments for concentrating virus in seawater have been carried out [ 20 ].…”