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Diseases of Aquatic Organisms

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DAO 72:9-17 (2006)  -  doi:10.3354/dao072009

Vaccine-associated systemic Rhodococcus erythropolis infection in farmed Atlantic salmon Salmo salar

A. B. Olsen1,*, T. H. Birkbeck2, H. K. Nilsen1, H. L. MacPherson2, C. Wangel3, C. Myklebust4, L. A. Laidler5, L. Aarflot6, E. Thoen7,8, S. Nygård9, T. Thayumanavan8,10, D. J. Colquhoun8

1National Veterinary Institute Bergen, PO Box 1263 Sentrum, 5811 Bergen, Norway
2Division of Infection and Immunity, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK
35993 Ostereidet, Norway
4Fjord-Lab AS, PO Box 7, 6701 Måløy, Norway
5Marine Harvest McConnell, Lochailort, Inverness-shire PH38 4LZ, UK
6Nordvest Fiskehelse, Dragsund, 6080 Gurskøy, Norway
7VESO Vikan AkvaVet, Vikan, 7800 Namsos, Norway
8National Veterinary Institute, PO Box 8156 Dep, 0033 Oslo, Norway
9Fiskehelse og Miljø AS, Ramsvollsv. 1, 5518 Haugesund, Norway
10Department of Environmental Sciences, Bharathiar University, Coimbatore 641046, India

ABSTRACT: In 7 instances between 2000 and 2003, clinical investigation of populations of fresh- and seawater-reared, vaccinated, Atlantic salmon Salmo salar suffering total losses of between 0.1 and 35% revealed infection with a Gram-positive rod-shaped bacterium. The isolations were geographically widespread, occurring in both Norway and Scotland. In all cases, a Gram-positive bacterium, subsequently identified as Rhodococcus erythropolis, was isolated in pure culture. Infections, although systemic, were focused within the peritoneal cavity. While initial attempts to reproduce the disease by intraperitoneal injection of unvaccinated Atlantic salmon failed, Koch’s postulates were subsequently fulfilled in fish vaccinated with a commercially available oil-adjuvanted vaccine.

KEY WORDS: Rhodococcus erythropolis · Vaccination · Atlantic salmon · Salmo salar · Disease · Pathology · Peritonitis

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