Fig. 7.

Tracheal sections from IBV inoculated birds. H&E. 200×. On day 6 pi, the Cal99-infected group had lesions characterized by moderate diffuse lymphocytic tracheitis with prominent deciliation, and multifocal squamous metaplasia; whereas, in the M41 inoculated birds, the lesions were most severe with extensive mononuclear cellular infiltration in the lamina propria. On day 10 pi, the tracheal epithelia of both the Cal99 and M41 inoculated groups were nearly normal in appearance with moderate accumulations of lymphocytes admixed with tissue macrophages and heterophils in the lamina propria. On day 14 pi, the Cal99-infected group had lesions characterized by focal lymphatic nodules in the lamina propria with desquamation of epithelium overlying the nodules; however, in the M41-inoculated groups, no lesions were observed although the thickness of the tracheal mucosa was slightly more than in the uninoculated negative control group. Virus re-isolation records (bottom signs): positive (+) indicates virus was isolated from every birds in a group, negative (−) indicates virus isolation was not successful from any bird in a group, and both positive and negative (±) indicates some birds were positive for virus isolation but some were not in a group