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Porcine parvoviruses display only very few genomic differences. Nevertheless, they can be segregated into four distinct groups with respect to their cellular tropism and pathogenicity. Chimeric constructs produced by exchanging restriction fragments between infectious clones of nonpathogenic and pathogenic strains permitted the identification of the allotropic determinant. This determinant contains only three amino acid changes which have been predicted to be located on external loops of the capsid protein. One of these differences, S436P, is probably located on top of the three-fold spike. Several lines of evidence indicate that tropism is determined by an intracellular interaction with host cell proteins and not by a distinguishing receptor. The expression strategy of these parvoviruses, which differs from the well-characterized MVM/H-1 group, and the importance for differential diagnosis and prevention are also discussed. |
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