Systematic Veterinary Virology

MORPHOLOGY

• DHV I (Enterovirus of Pircornaviridae)
  • The virions not enveloped and hence are not ether sensitive. The capsids are 28-30 nm in diameter and the symmetry is icosahedral. Nucleocapsids appear to be round.
  • Incomplete virus particles (empty capsids) are often observed. The virions contain one molecule of linear positive-sense single stranded RNA. Total genome contains 7400 nt. The 5' end of the genome has a protein (VPg). 3' end has a poly (A) tract.
• DHV II (Astrovirus)
  • The virions are not enveloped and hence are not ether sensitive. The capsid is round and exhibits polyhedral symmetry. The capsid surface structure reveals a regular pattern with distinctive features (star-like with six points).
  • The surface projections appear as small spikes protruding from the 12 vertices. The genome is not segmented and consists of a single molecule of linear positive-sense single-stranded RNA. The complete genome is about 6800-7900 nucleotides long. There is no poly A tail.