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Diseases of Aquatic Organisms

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DAO 47:119-128 (2001)  -  doi:10.3354/dao047119

Strain variation, based on the hemagglutinin gene, in Norwegian ISA virus isolates collected from 1987 to 2001: indications of recombination

M. Devold1, K. Falk2, O. B. Dale2, B. Krossøy3, E. Biering3, V. Aspehaug2, F. Nilsen1, A. Nylund1,*

1Department of Fisheries and Marine Biology, University of Bergen, 5020 Bergen, Norway
2National Veterinary Institute, Section of Aquatic Animal Health, 0033 Oslo, Norway
3Intervet Norbio, 5020 Bergen, Norway
*Corresponding author. E-mail:

ABSTRACT: Infectious salmon anemia (ISA) is caused by a virus that probably belongs to the Orthomyxoviridae and was first recorded in Norway in 1984. The disease has since spread along the Norwegian coast and has later been found in Canada, Scotland, the Faroe Islands, Chile, and the USA. This study presents sequence variation of the hemagglutinin gene from 37 ISA virus isolates, viz. one isolate from Scotland, one from Canada and 35 from Norway. The hemagglutinin gene contains a highly polymorphic region (HPR), which together with the rest of the gene sequence provides a good tool for studies of epizootics. The gene shows temporal and geographical sequence variation, where certain areas are dominated by distinct groups of isolates. Evidence of transmission of ISA virus isolates within and between regions is given. It is suggested that the hemagglutinin gene from different isolates may recombine. Possible recombination sites are found within the HPR and in the 5¹-end flanking region close to the HPR.

KEY WORDS: ISAV · Hemagglutinin · Strain variation · Recombination

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