Systematic Veterinary Virology

MORPHOLOGY

• The virus measures approximately 70-85nm in diameter. The virions not enveloped and hence are not ether sensitive. The capsid shell of virion is composed of two layers.
• The virus has icosahedral symmetry. The nucleocapsids appear to be round without any surface projections or distinct spikes. The outer layer contains two proteins, VP2 and VP5. VP2 is the major neutralising antigen and determinant of serotype specificity. This is followed by a core comprising of VP7, VP3 and three minor proteins and RNA. VP7 is a major determinant of serogroup specificity. VP7 can also mediate attachment of BTV to insect cells.
• The virions contain 10 segments of double stranded RNA. The total genomic length is 19200 nucelotides and the largest segment L1 has got approximately 2800-3900 nucelotides. The viral RNA has methylated cap structure, but no poly A tail.