Morphological studies of the respiratory syncytial virus induced bronchiolitis in experimentally infected calves

RSV-infections of the lower respiratory tract in infancy and early childhood are the most frequent causes of a hyperreactive bronchial system and obstructive lung disease. Studies concerning the morphological alterations of the bronchial mucosa during an RSV-infection are dependent on an experimental animal model. In this study the alterations of the lower respiratory tract from five infected colostrum-fed calves during the initial stage of the infection are described. BRSV strain 375 was applied as an aerosol on four consecutive days. The animals showed clinical symptoms already on the first day after infection. 7 days after the first infection the calves were necropsied. Lobular distributed atelectasis of the lung were found. The corresponding bronchioli were collapsed. The bronchiolar lumina were filled with a putrid exudate. In the bronchiolar wall a band-like lymphocytic infiltrate was found. By confocal laserscanning microscopy and by scanning electron microscopy intracellular viral components marked by an antibody against the viral P-protein were depicted. The intracellular virus inclusions were arranged along the bundles of filaments of the cytoskeleton. By transmission electron microscopy an alteration of the ciliogenesis and in cases of severe cell damage, cell death could be observed. The morphological findings suggest that the cytoskeleton plays an important role in the development of bronchiolitis.