The pathology and pathogenesis of experimental Mycoplasma hyorhinis infection of piglets with and without thermomotor stress. 2. Electron microscopic study results

: Electron microscopic investigations on the respiratory tract of piglets with and without Mycoplasma hyorhinis infection (10th day of life) partly combined with swim stress (15 degrees C water temperature) (n = 20/20) yielded the following results: colonization of Mycoplasma hyorhinis in the ciliary zone of trachea and bronchi in 15 out of 40 piglets (37.5%); the evidence rate of Mycoplasma hyorhinis in pneumonic lungs (8 out of 12 = 66.7%) was significantly higher than in nonpneumonic lungs (7 out of 28 = 25.0%) and highest in experimentally infected piglets with swim stress (9 out of 16 = 56.2%). Ultrastructural lesions: loss of cilia; bleb-formation; hydropic degeneration and desquamation of ciliary cells; the occurrence of cilia-free and immature epithelial cells; alveolar collapse; microatelectasis; oedematous swelling of pneumocyte I; accumulation of surfactant in the alveoli; hyperplasia of pneumocyte II; exudation of mononuclear macrophages and neutrophils with numerous digestion vacuoles; several lymphocytes and plasma cells, only a little lymphohistiocytic interstitial and peribronchial infiltration. Phagocytized mycoplasmas were found within the resorption vacuoles of neutrophils in the tracheobronchial area, for this once in alveoli, not (more) against in alveolar macrophages. The results were discussed with regard to etiology and pathogenicity of enzootic pneumonia in pigs.