Notes on Genus: Isavirus

enveloped spheres or pleomorphic
enveloped spheres or pleomorphic

Type member: Infectious salmon anemia virus


General Description

The genus Isavirus B is a member of the family Orthomyxoviridae. It is named from the type (and only) member Infectious salmon anemia virus, which infects fish.


Virions spherical or pleomorphic, enveloped, 80-120 nm in diameter, with projections 4-6 nm in diameter and 10-14 nm long.


Single-stranded negative sense RNA in 8 segments totalling about 14.5 kb. The segments do not have a genome-linked protein (VPg) at their 5'-terminus nor a 3'-polyA tail.

Genus Genomic Organization

There are 8 RNA segments. The larger genome segments each encode a single protein while the two smallest segments each encode two proteins.

Type Member Genomic Organization

There are 8 RNA segments:
  • RNA1 (2.3 kb) encodes a basic polymerase (PB2) of 80 kDa
  • RNA2 (2.2 kb) encodes a basic polymerase (PB1) of 80 kDa
  • RNA3 (2.1 kb) encodes the coat protein (Nucleoprotein, NP) of 68 kDa
  • RNA4 (1.8 kb) encodes an acid polymerase (PA) of 65 kDa
  • RNA5 (1.5 kb) encodes an acetylesterase of 49 kDa
  • RNA6 (1.3 kb) encodes a hemagglutinin (HA) of 43 kDa
  • RNA7 (1.1 kb) encodes two matrix proteins (M1 and M2) of 34 and 17 kDa
  • RNA8 (0.9 kb) encodes two non-structural proteins (NS1 and NS2) of 27 and 22 kDa