Systematic Veterinary Virology

MORPHOLOGY

• The virions are non-enveloped and hence are not ether sensitive. The capsid is composed of a single layer and appear hexagonal in outline with icosahedra symmetry.
• The capsid consists of 132 capsomers and surface projections are not present. The virions measure 60 nm in diameter. Virions contain two segments of linear double stranded RNA.
• The genome contains 5850-6050 nucleotides. The largest segment is termed as A and is comprised of 3100-3200. The second largest segment is termed as B and is comprised of 2750-2850.
• The 5' end of the genome has on both segments a genome-linked protein (VPg) and the 3' end has no poly (A) tract. Segment A codes for four proteins VP2, VP3, VP4 and VP5. VP2 and VP3 are capsid proteins and VP4 and VP5 are non-structural proteins.
• The antigenic determinants are located in the VP2 protein. VP5 is cytotoxic in nature and responsible for lysis of cell during release of virus. Segment B contains only one gene, VP1, which codes for the virus polymerase.