Erosion and its subsequent lesions in fowl air sacs

Abstract

Histopathological investigation was carried out to clarify the pathogenesis of suchlesions of the fowl respiratory organs, especially the air sacs, as considered macroscopicallycharacteristic of chronic respiratory disease (CRD).The materials used for the present investigation had been collected from two groups, A and B. Group A consisted of 30 chickens from 12 to 328 days of age which had beenproved macroscopically to have caseous masses in the air sacs. Group B was composed of36 individuals, including unpipped embryos, pipped embryos, and day-old cull chicks, which had been demonstrated histopathologically to have Iesions in the air sacs. All thematerials were derived from naturally infected cases. At necropsy, as many samples aspossible were collectecl from various parts of the air sacs (cervical, interclaxzicular, anteriorthoracic, posterior thoracic, and abdominal air sacs) for histological examination.The results obtained are summarized as follows.I) In groups A and B, the lesions of the air sacs and such related respiratory organsas the lungs and the tracheas could be classified into the same category. Moreover, theselesions were very similar to those of what is commonly called "CRD".2) Qualitatively, the degeneration and substance defect (erosion) in the epithelialcell layer of the air sacs were considered as an initial Jesion of the disease. The degener-ation of the epithelial cells subsequently became coagulative necrosis. Sucla degenerativelesions had the appearance of large or small patches and were frequently accompanied bythe disappearance of epithelial cells (substance defect). These findings were the mostfrequent and typical lesions of the air sacs, especially in group B. Moreover, degenerativechanges of the respiratory epithelial cells could be pointed out in tlte lungs and thetrachea witlaout any difficulty.3) Exudative detritus masses whicla had stained with eosin were deposited at the siteof substance defect. Subsequenttly they induced dilatation to the lumina of the air sacsand the bronchi. findings as formation of granuloma. The present author, however, cannot agree withthem, because epithelial cells and their derivatives are mainly involved in this prolifer-ative change.As another type of activation of epithelial cells, the formation of ttubular architecturewas very interesting. It was observed mostly in the epithelial cell layer beneath the exuda-tive foreign bodies and characterized by the formation of a monolayer of hyperplastic epi-thelial cells.5) It may be considered that as initial Iesions, inflammatory changes occurred tothese air sacs as the result of degeneration and erosion of the epitltelial cell layer. Ofthese changes, especially the infiltration of small round cells was generally mild. Most ofthe previous workers regarded these changes as pathognostic lesions of Mycoplasma infec-tion, which they called "lymphatic follicular nodules" and other terms. The presentauthor understood that these changes were simple cellular reactions which included sub-acute and chronic inflammatory changes, and were accompanied by proliferation of sub-epithelial tissue.6) In regard to the degree and distribution of these Iesions, groups A and B showeda marked contrast to each other. In the air sacs, the high degree of Iesions was most Ire-quently observed in group A (57%) and the low degree in group B (56%). In the lungs, the medium degree of lesions was most frequently observed in group A (37%) and thenormal state without lesions in group B (72%).In respect to the distribution of lesions in the air sacs, the cases most frequently ob-served were those accompanied by lesions in all the five air sacs in group A (577) andthose accompanied by lesions in only one of the five air sacs in group B (337). [the rest omitted]