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Diseases of Aquatic Organisms

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DAO 146:41-52 (2021)  -  DOI: https://doi.org/10.3354/dao03618

Early detection of salmonid alphavirus in seawater from marine farm sites of Atlantic salmon Salmo salar

Lisa-Victoria Bernhardt1,*, Atle Lillehaug1, Lars Qviller1, Simon Chioma Weli1, Estelle Grønneberg1, Hanne Nilsen2, Mette Myrmel3

1Norwegian Veterinary Institute, PO Box 64, 1431 Ås, Norway
2Norwegian Veterinary Institute, PO Box 1263 Sentrum, 5811 Bergen, Norway
3Norwegian University of Life Sciences, Faculty of Veterinary Medicine, Virology Unit, PO Box 5003, 1432 Ås, Norway
*Corresponding author:

ABSTRACT: The traditional strategy for national surveillance of salmonid alphavirus (SAV) infection in Norwegian fish farms relies on a costly, time-consuming, and resource-demanding approach based on the monthly sampling of fish from all marine farms with salmonids. In order to develop an alternative surveillance method, a water filtration method was tested in parallel with the ongoing surveillance program at 7 Norwegian marine farm sites of Atlantic salmon Salmo salar L. with no current suspicion of SAV infection. During the period from May 2019 to January 2020, seawater samples were collected from the top layer water inside all net-pens at these 7 sites. The samples were concentrated for SAV by filtration through an MF-Millipore™ electronegative membrane filter, followed by rinsing with NucliSENS® Lysis Buffer, before RNA extraction and analysis by RT-qPCR. SAV was detected from seawater at an earlier stage compared to traditional sampling methods, at all sites where the fish tested positive for SAV. A significant negative relationship was observed at all sites between the SAV concentration found in seawater samples and the number of days until SAV was detected in the fish. This means that the fewer the SAV particles in the seawater, the more days it took until SAV was detected in the fish samples. Based on this, sampling of seawater every month for the surveillance of SAV has a great potential as an alternative method for early detection of SAV in Atlantic salmon farms.


KEY WORDS: Surveillance · Water filtration · SAV detection · SAV concentration · Salmonid alphavirus · Pancreas disease · RT-qPCR · Field study


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Cite this article as: Bernhardt LV, Lillehaug A, Qviller L, Weli SC, Grønneberg E, Nilsen H, Myrmel M (2021) Early detection of salmonid alphavirus in seawater from marine farm sites of Atlantic salmon Salmo salar. Dis Aquat Org 146:41-52. https://doi.org/10.3354/dao03618

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