Distribution of porcine reproductive and respiratory syndrome virus in stillborn and liveborn piglets from experimentally infected sows

Four pregnant sows were infected 3 weeks before their expected farrowing da te with a Korean isolate (North American genotype) of porcine reproductive and respiratory syndrome virus (PRRSV). The distribution of virus in their stillborn and liveborn (killed 7 days after birth) offspring was assessed i mmunohistochemically and by in-situ hybridization. PRRSV antigen and nuclei c acid were detected in lung, thymus, liver, tonsil, spleen, heart, kidney and lymph nodes from both stillborn and liveborn piglets. Positive cells ty pically exhibited a red (immunohistochemistry) or dark brown (in-situ hybri dization) reaction product in the cytoplasm, without background staining. T he most consistent labelling for PRRSV was in the thymus, tonsil and lymph nodes. The experiment suggested that, in prenatal piglets, PRRSV replicates primarily in lymphoid tissues, having gained access to them from the place nta via the bloodstream. (C) 2001 Harcourt Publishers Ltd.