A review of infectious interstitial and bronchointerstitial pneumonia in cattle with an algorithm for the detection of infectious and non-infectious causes

Bovine interstitial and bronchointerstitial pneumonias are common and important diseases of cattle, caused by several infectious and non-infectious causes. Here, we review the roles of bovine respiratory syncytial virus, bovine parainfluenza virus 3, bovine alphaherpesvirus 1, bovine viral diarrhea virus, bovine coronavirus, influenza D virus, malignant catarrhal fever virus, and bovine adenovirus in interstitial or bronchointerstitial pneumonia. We describe the possible causes, pathogenesis, and diagnosis of bacterial septicemias that result in interstitial pneumonia, including <i>E. coli</i>, <i>Salmonella</i>, and <i>Pasteurella multocida</i> septicemias. We also review the parasitic causes of interstitial or bronchointerstitial pneumonia, primarily <i>Dictyocaulus viviparus</i>. Reaching a definitive postmortem etiologic diagnosis of interstitial or bronchointerstitial pneumonia can be challenging because infectious and non-infectious causes may look very similar grossly. Moreover, other conditions-that do not cause interstitial or bronchointerstitial pneumonia but rather pulmonary edema, congestion, and hemorrhage-can resemble interstitial pneumonia grossly. To guide the process of diagnosing interstitial and bronchointerstitial pneumonia, we offer an algorithm that integrates findings obtained from postmortem examination and ancillary laboratory testing. Our algorithm includes details on the gross characteristics of the lungs with interstitial or bronchointerstitial pneumonia, and we discuss other disease processes that may grossly resemble interstitial pneumonia. We highlight the key histologic features for differentiating specific causes and describe the most common ancillary laboratory tests to detect infectious and non-infectious causes.