Isavirus salaris is an enveloped, slightly pleomorphic virus belonging to the family Orthomyxoviridae. Virions are approximately 100–130 nm in diameter and possess surface projections characteristic of orthomyxoviruses. The viral genome consists of eight segments of negative-sense single-stranded RNA with a total length of approximately 14.5 kb. The virus replicates in endothelial cells and is the causative agent of Infectious Salmon Anemia (ISA), a severe disease of Atlantic salmon. The virus possesses surface glycoproteins involved in attachment and entry into host cells, including the hemagglutinin-esterase (HE) glycoprotein, which is a major antigenic determinant and has been investigated for use in recombinant vaccine development.