Virological and pathomorphological aspects in experimental infections with some triassociated pneumotropic viruses in the white mouse.

Experimental infections were induced in white mice by intranasal administration of parainfluenza virus type 3, 739-2D strain, to which influenza virus A/Beijing, 353/89 (H3N2) strain, and respiratory syncytial virus, Long strain, were associated. The model was organized so as to obtain a triassociated infection, parainfluenza virus type 3 being inoculated the first and the other two viruses, in the following stages-II and III-, alternately. The infections were revealed by the presence of positive immunofluorescence reactions in the pulmonary tissue, of histological, histochemical and histoenzymatic lesions at the level of the respiratory apparatus, as well as of pathomorphological changes in other organs. At the pulmonary parenchyma level the inflammatory lesion had a 100% frequency. The severest pathomorphological picture was the diffuse, lymphohistiocytic and macrophagic bronchopneumonia. The cytoinfiltrate was characterized by a proportionality between lymphocytes and histiocytes and the lower but not insignificant presence of macrophages. The prevalent lesion was the thickening of interparietoalveolar septa, as a consequence of stasis hyperemia, oedema and lymphohistiomacrophagocytic infiltrate, to which dystrophic lesions, especially of biocytes, are often added. Different lesions are present in other organs, such as: in the liver-inflammatory, dystrophico-inflammatory and dystrophic lesions; in the kidney, pancreas, cerebellum and thymus--vascular changes, stasis hyperemia; in the spleen--hyperplasia of megakaryocytes. Generally, the type and severity of lesions vary from one viral-association-induced infection to another.