Histologic pulmonary, tracheal and esophageal lesions in infected ball pythons. (A-F): hematoxylin and eosin staining, magnification 400-600X. (G,H): Gram-staining, magnification 1000X. (A,C,E): histology of uninfected snake; (B,D,F): histology of infected snakes. The lungs from infected snakes (B) were characterized by marked pneumocyte hyperplasia and mixed mononuclear and granulocytic inflammation compared to the uninfected snake (A). The normally thin and ciliated tracheal mucosa (C) was severely thickened in infected snakes (D) with epithelial necrosis, loss of the ciliated mucosal border and moderate mixed inflammation. The esophageal mucosa that is normally rich with mucus-producing epithelial cells (E) was also severely hyperplastic in infected snakes, with necrosis and mixed inflammatory infiltrates similar to those seen in the trachea (F). Gram-negative bacteria are present in snake with bronchopneumonia (H) but not in snake without bronchopneumonia (G).