Comparative Histopathology of Bovine Acute Interstitial Pneumonia and Bovine Respiratory Syncytial Virus-Associated Interstitial Pneumonia.

Acute interstitial pneumonia (AIP) is a significant disease of cattle and many aetiologies have been implicated on the basis of the characteristic pathological lesions. Bovine respiratory syncytial virus (BRSV) is one of the key aetiological factors in bovine respiratory disease complex and several studies have suggested, controversially, that BRSV may be an underlying cause of bovine AIP. BRSV infection is known to cause several distinctive histopathological changes, including epithelial syncytia formation and intracytoplasmic viral inclusions. However, distinguishing bovine AIP from BRSV-related pneumonia by clinical presentation, gross pathology or histopathology can sometimes be challenging. In order to identify the potential distinguishing features, we compared the histopathological findings of AIP that were, and were not, associated with BRSV infection in naturally occurring cases. We found that multinucleated giant cells were more frequently identified in cattle with AIP while bronchiolitis was more common in BRSV-infected cattle. However, this was not considered a sole indicator of either disease group. Statistically, we identified that a combination of several histopathological features, including alveolar septal necrosis, presence of multinucleated giant cells and bronchiolitis, can serve as an excellent indicator for distinguishing between idiopathic AIP and BRSV-related pneumonia, with a strong statistical significance (P = 0.0004). Based on the results of this retrospective study, we present a histopathological scoring system for predicting BRSV-associated AIP.