Experimental subacute foal pneumonia induced by aerosol administration of Corynebacterium equi

Subacute pyogranulomatous pneumonia was experimentally induced in 3 neonatal foals following multiple challenge with aerosols containing Corynebacterium equi. On each of 7 consecutive days the foals were exposed to approximately 3.5 X 10(7) viable C equi in droplets small enough to reach the terminal airways. Clinical, pathological and bacteriological features of the induced syndrome were indistinguishable from those exhibited by cases with spontaneous subacute C equi foal pneumonia. Radiographic evidence of advanced pulmonary damage preceded the appearance of clinical signs and ante mortem cultures were not consistent in determining the presence of C equi infection. As observed in spontaneous cases of C equi foal pneumonia, there was lymphocytic hyperplasia in the T-dependent paracortical areas of bronchial lymph nodes and spleen, and granulomatous pulmonary lesions. These histological changes suggested predominant stimulation of cell-mediated immune processes in C equi infected foals. Lesions were restricted to the lungs and pulmonary lymph nodes and C equi was recovered from each foal's lung tissue at necropsy; the organism was also cultured from the trachea, mediastinal lymph nodes, mesenteric lymph nodes and caecal contents of one foal and from the liver of another foal. Three control foals exposed to saline did not develop evidence of pneumonia.