Scoping review of clinical signs, etiologies, pathology findings, risk factors, and treatments of acute interstitial pneumonia in North American feedlot cattle

Acute interstitial pneumonia (AIP) has been a recognized bovine respiratory disease for many decades, yet the sporadic occurrences of AIP in feedlot cattle are poorly understood. We searched 3 databases (PubMed, CABI Direct Library, AGRICOLA) for primary literature on North American feedlot cattle, with a focus on interstitial pneumonia. We comprehensively reviewed reports of clinical signs, pathology findings, etiologies, risk factors, and treatments associated with AIP in feedlot cattle and identified gaps in knowledge. We included 19 peer-reviewed studies from 1976 to 2023. In 6 articles, the most common clinical signs for diagnosing AIP were severe dyspnea, increased expiratory effort, and grunting while breathing. In the 17 articles that provided detailed descriptions of the pathology and diagnostic features of AIP, consistent postmortem examination findings were interlobular edema and emphysema, a checkerboard appearance, and diffusely overinflated lung lobes. The most frequent histopathology findings were hyaline membranes, type II pneumocyte hyperplasia, and obliterative bronchiolitis. Although some potential etiologies, such as bovine respiratory syncytial virus (BRSV) and 3-methylindole (3MI), have been evaluated, no definitive cause has been identified consistently. Risk factors significantly associated with AIP in multiple studies included heifers, clinical onset at >45 days on feed (DOF), death at >78 DOF, and summer; the exact mechanisms remain unclear. The absence of standardized diagnostic criteria, along with a lack of research into potential effective prevention or treatment, underscore the need for further study to clarify the causes, diagnosis, and treatment of AIP in feedlot cattle.