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Title: Studies in the pathology of the respiratory system of the dog in virus infections
Author: Watrach, Adolf Michael
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1958
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Abstract:
The viral involvements of the respiratory system in animals and man from a morphologically distinct group of pathological conditions. The changes produced in the lung tissue by the action of viruses present a remarkable picture and have attracted much attention in the last three decades. Among the canine viral infections, distemper appears to be the only disease entity which consistently shows its effects on the respiratory tract and displays pulmonary lesions characteristic of all viral pneumonias. The present study was undertaken with the intent of supplementing and enlarging upon the available but scanty information on the pathology of the respiratory system, in distemper. It embodies the results of observations on the morbid anatomy and histopathology of the entire tract and bacteriology of the lung. The material on which the findings are based comprises thirty naturally occurring and twenty experimental cases of the disease. In the course of the investigations, special attention has been paid to the HISTO-pathological aspect of pneumonia. Some of the changes observed involve the long debated issue of the ultimate nature of the alveolar lining and required for their interpretation additional, electron microscopic studies on the normal structure of the pulmonary alveolar wall. Clinical signs of the disease and lesions in the respiratory tract were considerably more severe in the naturally occurring than in the experimental cases of distemper. Only mild malaise and slight changes were seen in the dogs suffering from experimental infection. These observations are in accord with those of previous workers. The gross lesions encountered in the clinical cases were generally most prominent between the third and fifth weeks of illness. The abnormalities observed in the pulmonary tissue included (a) congestion, often focal in distribution; (b) oedema; and (c) occasional subpleural consolidation. No oedema of the lung was found in the experimental dogs. Bacterial involvements of the lung were much more frequent in "street" distemper. Of the twenty experimental cases, only five yielded positive cultures, whereas most of the naturally infected dogs showed some degree of secondary infection. The strains of bacteria isolated from these cases included Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, staphylococci, streptococci and, in one dog, Brucella bronchiseptica. One of the salient features of pneumonia was the interstitial cellular reaction. It manifested itself as a mononuclear infiltration of the bronchiolar walls, the adjacent interalveolar septa and, often, of the perivascular connective tissue. Other changes intimately associated with the disease process included hyperplasia of the alveolar epithelium, accumulation of a chiefly mononuclear exudate in the region of gaseous exchange, and oedema of alveolar and, not infrequently, of perivascular spaces. The combined observations on the clinical and experimental cases of pneumonia revealed that the first tissue changes took place at the time of the initial rise in body temperature. The early signs of viral activity were shown not only by the cellular exudative phenomena but also by the appearance of cytoplasmic inclusion bodies in the bronchiolar epithelium. A few of these bodies were seen on the first day of illness. Quite early in the disease process the oedema fluid started to collect in alveoli and around smaller vessels. Epithelial cells of some of the bronchioles showed a degree of glycogenic infiltration which in later stages resulted in partial denudation of the mucous membrane. With the progress of the d3.sease, many mononuclear cells accumulated in the affected areas, and occasional polymorphonuclear leucocytes appeared in the alveolar spaces. Some of the intra-alveolar macrophages enlarged considerably and displayed multiple nuclei. At the end of the first week, the lining of the alveoli showed signs of proliferative activity. As a result of this process, many peribronchiolar and subpleural alveoli become lined by a pavement of usually flat cells. Such "epithelialisation" was evidently due to hyperplasia of the alveolar epithelium. This observation is supported by the electron Microscopic study of the normal lung which revealed that the pulmonary alveolar wall is lined by an uninterrupted although very tenuous epithelial membrane.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.777079  DOI: Not available
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