DAO 72:125-133 (2006)  -  doi:10.3354/dao072125

Virological, serological and histopathological evaluation of fish strain susceptibility to experimental infection with salmonid alphavirus

M. F. McLoughlin1,*, D. A. Graham2, A. Norris3, D. Matthews4, L. Foyle5, H. M. Rowley2, H. Jewhurst6, J. MacPhee7, D. Todd2

1Aquatic Veterinary Services, 35 Cherryvalley Park, Belfast BT5 6PN, Northern Ireland
2Veterinary Sciences Division, Department of Agriculture and Rural Development for Northern Ireland, Stoney Road, Belfast BT4 3SD, Northern Ireland
3Marine Harvest Ireland Ltd., Kindrum, Letterkenny, Co Donegal, Ireland
4Biometrics Branch, Department of Agriculture and Rural Development for Northern Ireland, New Forge Lane, Belfast BT9 5PX, Northern Ireland
5Department of Veterinary Pathology, Faculty of Veterinary Medicine, University College Dublin 4, Dublin, Ireland
6Queen’s University of Belfast, Stoney Road, Belfast BT4 3SD, Northern Ireland
7Marine Harvest Scotland Ltd., Trails Unit, Lochailort PH38 4LZ, Inverness-shire, UK

ABSTRACT: Pancreas disease (PD) of farmed Atlantic salmon Salmo salar L., which is caused by an alphavirus known as salmon pancreas disease virus (SPDV), can have serious economic consequences. An epidemiological survey carried out in Ireland in 2003 indicated that within individual farms there were significant differences in the susceptibility of different strains of farmed Atlantic salmon to infection with SPDV, as measured by levels of clinical disease and mortality. The aim of this preliminary study was to investigate this field observation by comparing lesion development, viraemia and serological responses of 3 commercial strains of Atlantic salmon (A, B and C) experimentally infected with SPDV. Highly significant differences in the severity of lesions in the pancreas at Day 21 post-infection (pi) were detected (p < 0.01), with Group B being more severely affected. There were also significant differences in the prevalence and severity of lesions in heart and skeletal muscle at Day 21 and 35 pi respectively, with Group B results again significantly higher than those from both Groups A and C (p < 0.05). There was no overlap between viraemia and the presence of specific SPDV antibody. Some fish in all groups had no viraemia, lesions or evidence of seroconversion. There were no significant differences seen between the challenged groups in relation to the percentage of viraemic fish at each time point. Viral loads were not determined. Differences between the number of antibody-positive fish in each challenge group were found at Days 28 and 35 pi (p < 0.1). Highly significant differences (p < 0.01) in the geometric mean titres of seropositive fish were detected at Day 28. These results, obtained using a challenge model, confirm that there are strain differences in the susceptibility to experimental SPDV infection in commercial farmed Atlantic salmon.


KEY WORDS: Salmon Pancreas Disease Virus · SPDV · Atlantic salmon · Disease susceptibility · Experimental challenge


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