[2][3] Viruses in family Birnaviridae are non-enveloped, with icosahedral single-shelled geometries, and T=13 symmetry.

Birnaviruses encode the following proteins: RNA-directed RNA polymerase (VP1), which lacks the highly conserved Gly-Asp-Asp (GDD) sequence, a component of the proposed catalytic site of this enzyme family that exists in the conserved motif VI of the palm domain of other RNA-directed RNA polymerases.

[6] Infectious pancreatic necrosis virus (IPNV), a birnavirus, is an important pathogen in fish farms.

Analyses of viral proteins showed that VP2 is the major structural and immunogenic polypeptide of the virus.

The variable domain of VP2 and the 20 adjacent amino acids of the conserved C-terminal are probably the most important in inducing an immune response for the protection of animals.