Systematic Veterinary Virology

GENERAL CHARACTERS

Morphology

• Virions are not enveloped and hence are not ether sensitive. The capsid/nucleocapsid is round and exhibits icosahedral symmetry. The virions measure 18-26nm diameter and consist only of protein (50%) + DNA (50%). The capsid is round and consists of 60 capsomers. The surface projections are small and surface appears rough with distinct spikes. There are three capsid proteins, VP1-3. VP2 is essential for virulence.
• The capsids can be penetrated by stain and some appear dark in the centre. The genome is not segmented and consists of a single molecule of linear negative-sense, or negative-sense and positive-sense single-stranded DNA. The complete genome is 5000 nucleotides long. Palindromic sequences are found at the 3’ and 5’ end of the genome.

Classification

• As per the VIII report of ICTV, the family Parvoviridae is divided into two subfamilies Parvovirinae and Densovirinae. These two subfamilies have been further subdivided into 5 and four genera respectively.