Studies in pneumonia of animals

Four groups of sheep were selected and examined post mortem for evidence of pneumonia. The conditions observed were atypical pneumonia, acute necrotising pneumonia (so- called "enzootic pneumonia "), pulmonary adenomatosis, pulmonary abscesses, pulmonary aspergillosis, aspiration pneumonia, pneumonia of haematogenous origin and pneumonia characterised by exudative and proliferative lesions. The latter has been described previously in sheep introduced into pens at the Moredun Institute (Stamp and Nisbet, 1963; Gilmour and Brotherston, 1963) but the histopathological lesions described were of a non -specific nature. Two outbreaks of respiratory disease in recently introduced sheep were investigated. In the first outbreak, acidophilic cytoplasmic inclusions in bronchial and bronchiolar epithelial cells and in alveolar lining cells were observed, providing affected sheep were killed early in the course of the disease. Other lesions such as syncytium formation, pseudo -epithelialisation of alveoli and hyperplasia of the bronchiolar epithelium were also present. Similar acidophilic cytoplasmic inclusions and proliferative lesions were seen in young lambs inoculated via the respiratory tract with an ovine strain of parainfluenza 3 (P13) virus. The inclusions, which were shown to represent aggregates of virus using immunofluorescence and electron microscopy, are of transient duration. The fact that these inclusions persist for only eight days after inoculation indicates the necessity of obtaining material within that time if P13 virus is to be implicated on histopathological grounds in natural outbreaks of respiratory disease. Qualitatively similar lesions were observed in lambs inoculated with a bovine strain of P13 virus and in calves inoculated with an ovine strain of P13 virus. If slaughter of affected sheep, in natural outbreaks of respiratory disease, was delayed, acidophilic cytoplasmic inclusions were absent and the histological lesions resembled those described for atypical pneumonia (Stamp and Nisbet, 1963). Inoculation of lambs with Bedsonia organisms resulted in a marked clinical response and macroscopic lesions of pneumonia. Bedsonia elementary bodies were numerous in cryostat sections of lung from lambs killed three and five days after inoculation but were difficult to detect in the lungs of lambs killed on days nine and twelve. The histological lesions in the lungs of lambs killed three and five days after inoculation were characterised by foci of necrosis and a sero- cellular exudate in alveoli and bronchioles, whereas, in lambs killed nine and twelve days after inoculation the principal lung lesions were hyperplasia of the bronchiolar epithelium, pseudo -epithelialisation and epithelialisation of alveoli and infiltration of the interalveolar septa by macrophages and lymphocytes. In the later stages of infection in lambs inoculated with either P13 virus or Bedsonia organisms, histological lesions which resembled those of atypical pneumonia were observed. It is considered therefore, that atypical pneumonia of sheep (Stamp and Nisbet, 1963) is not a specific entity. In the second outbreak of respiratory disease in sheep at the Moredun Institute a pneumonia morphologically distinct from those hitherto described was studied. The salient histological features were hyperplasia of the bronchiolar epithelium, marked alveolar epithelialisation, macrophage infiltration of alveoli and hyperplasia of the reticulin network around affected bronchioles and alveoli. The possible relationship of this condition to other epithelialising pneumonias is discussed. In a histological study of respiratory disease in intensively- reared calves, two types of pneumonia were encountered. One was characterised by bronchitis, bronchiolitis, a cellular exudate in alveoli, syncytium formation, alveolar epithelialisation and acidophilic cytoplasmic inclusions. It was concluded that the lesions were due to concomitant P13 virus and bacterial infections. The histological lesions of the second type consisted of peribronchial and peribronchiolar lymphocytic hyperplasia, atelectasis and mild interstitial pneumonia. A. comparison of the amount of intrapulmonary lymphoid tissue in apparently normal calves and in calves which had experienced a respiratory infection showed that in either group, the degree of peribronchial or peribronchiolar lymphocytic hyperplasia varied.