Interstitial pneumonia and lymphocytic bronchiolitis with interstitial emphysema of unknown cause in Western Canadian fetal and neonatal beef calves

Interstitial pneumonia and lymphocytic bronchiolitis with interstitial emphysema is an unusual reaction pattern in fetal and neonatal calves. These changes often are thought to suggest a chronic bacterial infection acquired in utero, and an associated placentitis is expected. Viral agents can also be implicated. Specific known pathogens that can induce a similar inflammatory response include <i>Ureaplasma diversum</i>, <i>Mycoplasmopsis bovis</i>, <i>Brucella abortus</i>, bovine viral diarrhea virus, and bovine parainfluenza virus 3. We describe a series of 15 cases of interstitial pneumonia and lymphocytic bronchiolitis with interstitial emphysema in fetal and early neonatal (up to 3-d-old) beef calves collected over 10 y in Alberta, Canada. Where reported, calves appeared small, weak, and occasionally were dyspneic. On autopsy, lungs appeared diffusely voluminous with interstitial emphysema, bulla formation, and rarely mediastinal emphysema and pneumothorax. A few calves had additional features of bacterial infection, such as pericarditis. Placenta was not received. Histologic lung findings in the affected calves included alveolar septa expanded by mononuclear cells, sparse neutrophils and macrophages within alveoli, variable lymphocytic and histiocytic peribronchiolar cuffing, prominent lymphoid aggregates surrounding bronchioles, occasional vascular necrosis, and subpleural and interlobular emphysema. PCR testing and immunohistochemistry for the previously noted pathogens were negative, and the cause of this unique condition, although presumably infectious, remains unknown.