Plaque morphology and pathogenicity for newborn mice of swine vesicular disease virus. I. Wild strains and their clones.

The population of wild swine vesicular disease virus (SVDV) strains was found non-homogeneous as manifested by varying plaque size and different pathogenicity of the clones obtained. The clones derived from large plaques (5-9 mm)--dominating among wild strains--were more virulent for newborn mice than those obtained from smaller plaques (1-2 mm). To evaluate the pathogenicity of wild SVDV strains the dose index was calculated; the clones were compared by dose index and theoretical pathogenicity index, respectively.