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Diseases of Aquatic Organisms

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DAO 46:173-179 (2001)  -  doi:10.3354/dao046173

Evidence for a carrier state of infectious hematopoietic necrosis virus in chinook salmon Oncorhynchus tshawytscha

Sophie St-Hilaire1,2,*, Carl Ribble2, Garth Traxler1, Tim Davies1, Michael L. Kent1,**

1Pacific Biological Station, Nanaimo, British Columbia V9T 1E1, Canada
2Department of Population Medicine, University of Guelph, Guelph, Ontario N1G 2W1, Canada
*E-mail: **Present address: Department of Microbiology, 220 Nash Hall, Center for Salmon Disease Research, Oregon State University, Corvallis, Oregon 97331-3804, USA

ABSTRACT: In British Columbia, Canada, infectious hematopoietic necrosis virus (IHNV) is prevalent in wild sockeye salmon Oncorhynchus nerka and has caused disease in seawater net-pen reared Atlantic salmon Salmo salar. In this study, chinook salmon Oncorhynchus tshawytscha experimentally exposed to an isolate of IHNV found in British Columbia became carriers of the virus. When Atlantic salmon were cohabited with these virus-exposed chinook salmon, IHNV was isolated from the Atlantic salmon. Identification of chinook salmon populations that have been exposed to IHNV may be difficult, as virus isolation was successful only in fish that were concurrently infected with either Renibacterium salmoninarum or Piscirickettisia salmonis. Also, IHNV-specific antibodies were detected in only 2 of the 70 fish experimentally exposed to the virus. Two samples collected from chinook salmon exposed to IHNV while at a salt water net-pen site had a seroprevalence of 19 and 22%; however, the inconsistencies between our laboratory and field data suggest that further research is required before we can rely on serological analysis for identifying potential carrier populations. Because of the difficulty in determining the exposure status of populations of chinook salmon, especially if there is no concurrent disease, it may be prudent not to cohabit Atlantic salmon with chinook salmon on a farm if there is any possibility that the latter have been exposed to the virus.

KEY WORDS: Infectious hematopoietic necrosis virus · Chinook salmon · Carrier state · Co-habitation study · Serology

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