Birnaviridae share no nucleic acid sequence similarity with other taxa. At the protein sequence level, the protein encoded by the A segment has no similarity with any other virus family. There is also no antigenic similarity detectable by antisera cross-reactivity. The RNA-dependent RNA polymerase (RdRp), encoded by segment B, does display evidence of conservation with other viral. The Birnavirus RdRps contain a hydrophilic, highly basic domain in the carboxy proximal region of the protein. Within this domain are conserved amino acids in positions that are found in other RdRps, particularly those of dsRNS viruses such as Reoviridae. The sequence conservation, however, is not sufficient to be detectable with any standard alogorithm for phylogenetic relatedness.

Picobirnavirus, the proposed name for a novel genus of viruses recently detected in children and several species of animals, is different from the existing members of the Family Birnaviridae. These viruses are 30-40 nm in diameter and have icosahedral symmetry with a triangulation number T = 3. Their buoyant density in CsCl is 1.4 g/cm3. Their genome is bi- or trisegmented dsRNA with segment lengths of 2.6 and 1.9 kbp for the bisegmented members of the group and 2.9, 2.4 and 0.9 kbp for the trisegmented genomes. These viruses are detected in the fecal material of animals with and without diarrhea.

Aqua: from Latin aqua, "water"
Avi: from Latin avis, "bird"
Bi: from Latin prefix bi, "two", signifies the bisegmented nature of the viral genome as well as the presence of dsRNA
Entomo: from Greek entomon, "insect"
Rna: sigla from ribo nucleic acid, indicating the nature of the viral genome

Leong JA, Brown D, Dobos P, Kibenge FSB, Muller H, Mundt E, Nicholson B