Pathological changes of tracheal mucosa in chickens infected with fowl pox virus.

Five-week-old chickens were inoculated with fowl pox (FP) virus and killed on various days through day 30 postinoculation (PI). The trachea was examined with a scanning electron microscope (SEM), a transmission electron microscope (TEM), and a light microscope (LM). From day 3 PI, small focal lesions of the mucosa were detected. On day 7 PI, upon formation of cytoplasmic inclusion bodies, epithelial cells proliferated profusely, enlarged, and formed clusters like papillomata. The disease proceeded to the gradual disruption of the lesions owing to the collapse of individual degenerating epithelial cells. Total desquamation of the lesions was observed. Ultrastructural examination revealed that the surface degenerating epithelial cells of the lesions ruptured and had virus particles inside. These changes were accompanied by severe inflammatory reaction. Thereafter, epithelial cells regenerated actively and the mucosa recovered by day 27 PI.