BAV is a small (72–75 nm in size), non-enveloped, double-stranded RNA virus surrounded by an icosahedral protein coat. Fibre proteins extend outward from the surface of the protein coat. The genome of BAV is about 19, 500 base pairs in length, linear and segmented into 12 parts, encoding for genes VP1-12. Seven of these, VP1-4 and VP8-10, are structural proteins. VP4 and VP9 form the outer protein coat. The inner particles of the coat are composed of VP1-3, VP8 and VP10. VP7 serves as a protein kinase, VP1 as an RNA-dependent RNA polymerase, VP3 as a capping enzyme, and VP12 as a dsRNA-binding protein.