Birnaviruses are bisegmented double‐stranded RNA viruses infecting animals belonging to different vertebrate and invertebrate phyla. Most of the research efforts on birnaviruses have focused on infectious bursal disease virus (IBDV), which is responsible for important losses in the poultry industry. Another economically important birnavirus is infectious pancreatic necrosis virus (IPNV) of salmonids. Other birnaviruses (<10) have been isolated from diseased animals, established cell lines or identified by deep sequencing. The reverse genetic systems that have been engineered for IBDV and IPNV at the end of the 1990s have been powerful tools to dissect the molecular biology of these viruses. During these past 10 years, resolution of the 3D‐structures of several birnavirus proteins (including their unique replicase/transcriptase, their protease, their capsid protein and ultimately their complete capsid) by X‐ray radiocrystallography, NMR and cryo‐electron microscopy shed light on important properties and characteristics of these viruses.

Key Concepts

  • Birnaviruses are nonenveloped double‐stranded RNA viruses with representatives able to infect animals of invertebrate and vertebrate phyla, but not yet found infecting mammals.
  • The birnavirus capsid possess a T = 13 laevo icosahedral symmetry.
  • Entry of birnavirus into a cell is mediated by a capsid‐associated peptide that deforms and perforates membranes.
  • The birnavirus virus protein 4 (VP4) protease possess a serine‐lysine catalytic dyad and is homologous to the protease domain of bacterial and organelle ATP‐dependent Lon proteases.
  • The birnavirus capsid protein VP2 is structurally homologous to the capsid protein of positive‐strand viruses, just like the T = 3 nodaviruses and T = 4 tetraviruses.
  • The palm subdomain‐based active site of the birnavirus RNA‐dependent RNA‐polymerases is internally permuted to the unique C‐A‐B motif arrangement, a feature shared with permutotetraviruses, a group of positive‐strand RNA viruses.
  • The capsid proteins of birnaviruses display a high structural polymorphism of their assemblies.

Keywords: molecular virology; double‐stranded RNA virus; diseases of poultry; fish diseases; nonenveloped virus; T = 13 laevo capsid; virus evolution

Figure 1. Birnaviruses infect species belonging to two vertebrate phyla, birds and teleost fishes, as well as to three invertebrate phyla, arthropods, mollusks and rotifers. They are reported as TV1, Tellina virus 1; RBV, Rotifer birnavirus; DXV, Drosophila X virus; ESV, Espirito Santo virus; DBV, Drosophila B virus; IBDV, infectious bursal disease virus; CPNV, chicken proventricular necrosis virus; IPNV, infectious pancreatic necrosis virus; BSNV, blotched snakehead virus.
Figure 2. Phylogenetic tree for the RNA‐polymerase (VP1) of eight birnaviruses. Maximum likelihood consensus tree. Numbers along the branches are the bootstrap values. Distance scale is displayed below the plot.
Figure 3. (a) Negative contrast electron micrograph of IBDV virions. Virions are about 60–70 nm in diameter. (b) View of IBDV particle. The shell domains of VP2 is coloured in yellow and the projection in red. (c) Diagram of an IBDV particle.
Figure 4. Schematic representation of the gene arrangement of segments A and B of birnaviruses. For segment A, the polyprotein is cotranslationally processed to generate pVP2, VP4 and VP3. During virus assembly, pVP2 is further processed to generate VP2 and structural peptides.
Figure 5. Sequence alignment of the pVP2‐specific domains of birnaviruses. The alignment is anchored to the multiple cleavage sites (vertical arrows) identified on BSNV, IBDVand IPNV, or proposed for DXV. * indicate residues conserved in the five sequences. Conserved prolines are indicated in bold. Double or single points indicate conservative substitutions.


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Further Reading

Delmas B, Mundt E, Wu JL and Vakharia VN (2011) Birnaviridae. In: King AMQ, Adams MJ, Carstens EB and Lefkowitz EJ, (eds.) Virus Taxonomy, pp. 497–508. Oxford: Elsevier.

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Kibenge FSB, Dillon AS and Russell RG (1998) Biochemistry and immunology of infectious bursal disease virus. Journal of General Virology 69: 1757–1775.

Lukert PD and Saif YM (1997) Infectious bursal disease. In: Calnek BW, Barnes HJ, Beard CW, Mc Dougald LR and Saif YM, (eds). Diseases of Poultry. Ames: Iowa State University Press.

McAllister PE (1993) Salmonid fish viruses. In: Stoskopf MK, (ed.) Fish Medicine. Philadelphia: WB Saunders.

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Delmas, Bernard(Feb 2015) Birnaviruses. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001009.pub2]