Distribution of a Korean strain of porcine reproductive and respiratory syndrome virus in experimentally infected pigs, as demonstrated immunohistochemically and by in-situ hybridization

In an experiment with 40 specific pathogen-free pigs aged 3 days, the distribution of a Korean isolate of porcine reproductive and respiratory syndrome virus (PRRSV) was assessed immunohistochemically and by in-situ hybridization for a period of 28 days after intranasal inoculation. The most consistent and intense labelling for PRRSV was in the lung, the virus persisting in pulmonary macrophages for at least 28 days. The middle lobe of the lung was the optimum site for the detection of PRRSV antigens and nucleic acids, and the interstitial macrophage was the main cell type in which PRRSV was identified. Other tissues and cells in which the virus was detected included macrophages and dendritic cells in the tonsil, lymph nodes, spleen and Peyer's patches, and macrophages in the hepatic sinusoids and adrenal gland. The experiment suggested that the pathogenesis of PRRSV infection may be summarized thus: initial entry of virus through tonsillar and pulmonary macrophages, followed within 3 days by viraemia and subsequent interstitial pneumonia.