Histopathology of infectious laryngotracheitis in fowl infected by an aerosol

Abstract

The gross and microscopic pathology of infectious laryngotracheitis in fowl infected by an aerosol is described. The trachea, lungs and air sacs were the main sites of damage and lesions were not seen in any organ outside the respiratory tract. Microscopic lesions were first apparent in the epithelial lining of the airways 48 hours after exposure. This was followed by extensive hyperplasia of the epithelium and intranuclear inclusion bodies were prominent in the hyperplastic epithelium. Inclusions persisted for up to 4 days after exposure to infection. Desquamation of the epithelium was complete by 5 days and this was followed by a period of rapid regeneration. Cilia was first observed in the regenerating epithelium 10 days after exposure and the mucosa had largely returned to normal by the 12th day. Pulmonary lesions were mainly concentrated in the primary bronchus and in the tertiary bronchi at the anterior and posterior ventral angles of the lungs. Lymphoid nodules were numerous in the walls of the tertiary bronchi from the 7th day onwards. By 15 days after exposure the amount of fluid exudate in the lumen of the tertiary bronchi was markedly reduced, but lymphoid nodules persisted in the walls of affected tertiary bronchi for the duration of the experiment. Giant cell syncytia containing intranuclear inclusion bodies were prominent in the air sac walls from the 3rd day after exposure. By 7 days fibroblastic proliferation was pronounced in the air sac walls in areas where epithelial damage was severe. This fibrous tissue was converted to dense collagen which persisted for the duration of the experiments.