The histopathology of infectious bronchitis in fowls infected with a nephrotropic "T" strain of virus.

The histopathology of the infectious bronchitis caused by the Cumming "T" strain of virus is described in fowls exposed to infection by an aerosol method. Desquamation of the ciliated and glandular epithelium throughout the trachea was seen 24 hours after exposure to virus. This was followed by rapid proliferation presumably of residual basal cells with the production of a stratified undifferentiated epithelial covering. Small areas of the tracheal submucosa showed lymphocytic infiltration by the 4th day. Cilia were first observed in the regenerating epithelium on the 7th day when mucous cells were also seen to be numerous. Alveolar mucous glands developed over the following 4 days and by the 12th day regeneration appeared complete. Pulmonary lesions were generally not severe and the air sacs were only slightly oedematous for 4 days following exposure. Necrosis of a few tubules scattered throughout the kidneys was seen on the 4th day. By the 6th day cystic tubules containing epithelial debris and polymorphonuclear leukocytes were prominent in both cortex and medulla and necrotic tubules were scattered throughout the kidneys. PAS positive granules were present in the renal tubular epithelium and were most pronounced in the distal convoluted tubules. Infiltration of the interstitium by lymphocytes and plasma cells was generally marked on the 7th day. The cytoplasm of these plasma cells was strongly PAS positive and such cells were most numerous on the 12th and 13th days after exposure and then their numbers rapidly declined. Regeneration of tubular epithelium was advanced by the 10th day and much of the cell debris had been cleared from the lumina of the tubules. What appeared to be compressed areas were seen in the cortex from the 13th day where glomeruli and tubules were numerous through considerably reduced in size. These were not seen after the 35th day, however an occasional lymph nodule persisted in the intersitium.