Scanning electron microscopy of trachea and bronchi from gnotobiotic pigs inoculated with Mycoplasma hyopneumoniae.

Areas of trachea and right apical and right dorsal diaphragmatic bronchi from gnotobiotic neonatal pigs were examined by scanning electron and transmission electron microscopy at 7, 13, and 21 days after pigs were given intranasal inoculation of Mycoplasma hyopneumoniae. Similar areas were examined by scanning electron microscopy from 2 noninoculated neonatal pigs. Tracheal and bronchial lesions were observed in all inoculated pigs. Severe bronchial lesions were in grossly affected lobes. Early infection consisted of mycoplasmas on ciliated epithelial cells. As the interval between inoculation and euthanasia increased, mycoplasmas and leukocytes on the tracheal and bronchial surfaces became more numerous and fewer cilia remained.