The putative polymerase sequence of infectious salmon anemia virus suggests a new genus within the Orthomyxoviridae.

The infectious salmon anemia virus (ISAV) is an orthomyxovirus-like virus infecting teleosts. The disease caused by this virus has had major economic consequences for the Atlantic salmon farming industry in Norway, Canada, and Scotland. In this work, we report the cloning and sequencing of an ISAV-specific cDNA comprising 2,245 bp with an open reading frame coding for a predicted protein with a calculated molecular weight of 80.5 kDa. The putative protein sequence shows the core polymerase motifs characteristic of all viral RNA-dependent RNA polymerases. Comparison of the conserved motifs with the corresponding regions of other segmented negative-stranded RNA viruses shows a closer relationship with members of the Orthomyxoviridae than with viruses in other families. The putative ISAV polymerase protein (PB1) has a length of 708 amino acids, a charge of +22 at neutral pH, and a pI of 9.9, which are consistent with the properties of the PB1 proteins of other members of the family. Calculations of the distances between the different PB1 proteins indicate that the ISAV is distantly related to the other members of the family but more closely related to the influenza viruses than to the Thogoto viruses. Based on these and previously published results, we propose that the ISAV comprises a new, fifth genus in the Orthomyxoviridae.