Progression of tracheal lesions in turkeys exposed by aerosol to LaSota strain of Newcastle disease virus.

Five-week-old turkeys were exposed by aerosol to the LaSota strain of Newcastle disease virus. Poults were killed on days 2, 4, 6, 8, 10, 12, and 14 postexposure, and tracheas were processed for virus quantitation and histologic examination. Newcastle disease virus was recovered at a high titer from all tracheas collected 2, 4, and 6 days postexposure. The initial tracheal lesion observed on day 2 was swelling of ciliated columnar and mucous gland cells. Some of the affected cells contained intracytoplasmic inclusions. Cell swelling and degeneration were followed by epithelial cell proliferation, fibrinopurulent exudation, and lymphocytic infiltration. Epithelial cell proliferation was most severe on days 4 and 6, when tracheas were lined with several layers of immature cells. Lymphoid nodules appeared on day 6 and persisted up to day 14. From day 8 on, there was regression of the proliferative lesion accompanied by differentiation of the immature epithelium. By day 14, the tracheal mucosa regained its normal histologic appearance.