Porcine reproductive and respiratory syndrome virus and Haemophilus parasuis antigen distribution in dually infected pigs

Immunohistochemical, viral and bacterial isolation techniques were used to study the distribution and localization of porcine reproductive and respiratory syndrome virus (PRRSV) and Haemophilus (H.) parasuis in experimentally infected pigs. Thirty pigs seronegative to PRRSV and H. parasuis were divided into four groups. Group A pigs (10 animals) were inoculated with both virus and bacteria; group B pigs (10 animals) were inoculated with bacteria, group C pigs (five animals) were inoculated with virus and group D pigs (five animals) were kept as negative controls. All pigs of groups A and C became infected with PRRSV, according to virological techniques used (immunohistochemistry, virus isolation and virus serology). Lung, heart and tonsils were the most frequently immunolabeled tissues, and monocyte/macrophage lineage cells were the target for PRRSV in all tissues. All pigs in groups A and B also became infected with H. parasuis based on immunohistochemical and bacterial isolation results. Serosal surfaces, lung and tonsils were the most frequently immunolabeled tissues, and bacteria were found in monocyte/macrophage lineage cells as well as within neutrophil cytoplasm. No differences in terms of bacterial distribution or localization in tissues of pigs of groups A and B were detected. These results suggest that there is no influence of the previous infection with PRRSV in the occurrence of H. parasuis infection.