Canine parvovirus capsid, molecular model. Canine parvovirus type 2 (CPV2) was first recognized in 1978 and spread worldwide in less than two years. It affects dogs and there are two forms of the disease; the more common intestinal form and the rarer cardiac form. A vaccine is available. In viruses, the capsid is the protein shell that encloses the genetic material. It consists of subunits called capsomeres that self-assemble to form the shell seen here. Here, this shell, approximately spherical in shape, has icosahedral symmetry. One of the capsid functions is to aid transmission of the viral genetic material into host cells.