PATHOLOGY OF AN EXPERIMENTAL-INFECTION OF SPECIFIC PATHOGEN-FREE LAMBS WITH PARA-INFLUENZA VIRUS TYPE-3 AND PASTEURELLA-HAEMOLYTICA

Forty-one SPF lambs were challenged with PI3 virus intratracheally and 4 or 7 days later with a Pasteurella haemolytica aerosol. Thirty-nine developed pneumonia and 22 died or were killed when severely ill within 6 days of administering the aerosol. On the first day after P. haemolytica challenge the pneumonia consisted of inflamed alveoli, scattered necrotic foci and a few hyaline membranes. Bacteria were numerous in all lesions. During day 2 pleomorphic cells with intensely basophilic nuclei invaded affected alveoli but subsequently only an alveolar capillary network and necrotic foci were found surrounded by a dense layer of pleomorphic cells. Outwith this layer, there formed a connective tissue capsule then a zone of consolidation consisting of alveoli lined by hypertrophied cells and enclosing macrophage-like cells. Similar alveolar consolidation without necrosis was found in locations remote from the main lesions. Some bronchioles in all lesions had a hyperplastic epithelium which was sloughed in parts, the cell debris forming lumenal plugs. This experimental pneumonia closely resembled that of naturally occurring pasteurellosis and was apparently unaffected in its morphological development by the preliminary PI3 infection. © 1979.