Tissue tropisms of porcine parvovirus in swine

Late-term gestation swine fetuses, similar to adult animals, are able to effectively mount immune response and survive porcine parvovirus (PPV) infection. An exception to this is the Kresse strain of PPV, which causes fetal death in late-term gestation swine fetuses. In an effort to understand the basis for this profound difference in pathogenicity between Kresse strain and the prototype strain of PPV, NADL-8, studies were designed to examine potential difference in sites of replication and quantity of virus produced between Kresse and NADL-8 strains. In order to define the sites of viral replication or sites of viral sequestration in situ hybridization, using digoxigenin-labeled strand-specific oligonucleotide probes, was applied to detect the presence of either double stranded viral DNA (RF) or viral single stranded DNA in tissues of infected fetuses. The presence and the state of viral DNA was confirmed by Southern blot hybridization. Relative amounts of RF-DNA synthesis in each tissue was compared between the two virus strains. Virus replication appeared to be of comparable levels in the livers of both NADL-8 and Kresse infected swine fetuses. Differences between these strains were observed in the brain and spleen; RF-DNA was detected in the brain and spleens of Kresse infected fetuses but not in NADL-8 infected ones. These findings indicate that differences in DNA replication of the PPV strains in selective sites, as well as the quantity of virus produced, may explain the distinction in pathogenesis of these viruses.