Detection of specific Atlantic salmon antibodies against salmonid alphavirus using a bead-based immunoassay

Lena Hammerlund Teige,Ida Aksnes,Magnus Vikan Røsæg,Ingvill Jensen,Jorunn Jørgensen,Hilde Sindre,Catherine Collins,Bertrand Collet,Espen Rimstad,Maria K Dahle,Preben Boysen

doi:10.1016/j.fsi.2020.07.055

Abstract

Salmonid alphavirus (SAV) is the etiological cause of pancreas disease (PD) in Atlantic salmon (Salmo salar). Several vaccines against SAV are in use, but PD still cause significant mortality and concern in European aquaculture, raising the need for optimal tools to monitor SAV immunity. To monitor and control the distribution of PD in Norway, all salmonid farms are regularly screened for SAV by RT-qPCR. While the direct detection of SAV is helpful in the early stages of infection, serological methods could bring additional information on acquired SAV immunity in the later stages. Traditionally, SAV antibodies are monitored in neutralization assays, but they are time-consuming and cumbersome, thus alternative assays are warranted. Enzyme-linked immunosorbent assays (ELISAs) have not yet been successfully used for anti-SAV antibody detection in aquaculture. We aimed to develop a bead-based immunoassay for SAV-specific antibodies. By using detergent-treated SAV particles as antigens, we detected SAV-specific antibodies in plasma collected from both a SAV challenge trial and a field outbreak of PD. Increased levels of SAV-specific antibodies were seen after most fish had become negative for viral RNA. The bead-based assay is time saving compared to virus neutralization assays, and suitable for non-lethal testing due to low sample size requirements. We conclude that the bead-based immunoassay for SAV antibody detection is a promising diagnostic tool to complement SAV screening in aquaculture.

Highlights

Salmonid alphavirus (SAV), named Salmon pancreas disease virus (SPDV) by the International Committee on Taxonomy of Viruses, is a widespread pathogen in European aquaculture, causing pancreas dis ease (PD) and sleeping disease (SD) in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) respectively
The six subtypes of SAV (SAV1-6) are geographically separated: SAV1 is common in Ireland and Scotland, SAV2 in rainbow trout reared in freshwater in continental Europe [1] as well as in salmonids in sea cages in England, Scotland and Norway [2], and SAV3 is common in Norway, where the disease has been recognized since 1989 [3]
We have previously showed that a Piscine orthoreovirus (PRV) infection induces production of non-specific, possibly polyreactive an tibodies [27], and found high background binding to beads coated with the irrelevant antigens: lipid-modified ICP11 protein from shrimp white spot syndrome virus (ICP11), lipid-modified infectious salmon anemia virus fusion protein (FP-LM) and an unmodified infectious salmon anemia virus fusion protein (FP)

Summary

Introduction

Salmonid alphavirus (SAV), named Salmon pancreas disease virus (SPDV) by the International Committee on Taxonomy of Viruses, is a widespread pathogen in European aquaculture, causing pancreas dis ease (PD) and sleeping disease (SD) in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) respectively. The diseases are widespread in Europe and may cause high fish mortality and reduced weight gain resulting in decreased fish welfare and great economic losses for the industry. The six subtypes of SAV (SAV1-6) are geographically separated: SAV1 is common in Ireland and Scotland, SAV2 in rainbow trout reared in freshwater in continental Europe [1] as well as in salmonids in sea cages in England, Scotland and Norway [2], and SAV3 is common in Norway, where the disease has been recognized since 1989 [3]. SAV-infected fish demonstrate reduced appetite, aberrant swimming, fecal casts and lethargy, and the population has increased mortality. The virus can spread between farms via water currents or moving

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