Presumptive hypersensitivity pneumonitis in dairy cattle: a case report

Hypersensitivity pneumonitis is a pathological condition caused by the continuous inhalation of various antigenic compounds, leading to an exacerbated immune response and subsequent lung injury. Although this condition has been reported in several animal species, it has not yet been documented in cattle in South America. This report describes a case that occurred in 2020 on a dairy farm operating under a dry-lot system with soil bedding, located in Buenos Aires province, Argentina. An increased frequency of respiratory cases was observed among lactating cows, occasionally resulting in death. Affected animals exhibited dyspnea, adynamia, orthopneic position, ptyalism, and normal rectal temperature. Postmortem examination of one affected cow revealed severe generalized pulmonary and mediastinal emphysema. Microscopically, mild to moderate thickening of the alveolar septa was observed, accompanied by increased infiltration of lymphocytes, macrophages, and neutrophils. The alveoli contained abundant multinucleated giant cells distributed multifocally, along with occasional macrophages and neutrophils, and multifocal areas of intra-alveolar edema. The interlobular septa were expanded due to lymphatic distension, edema, and a mild diffuse infiltration of macrophages and lymphocytes. Bacteriological cultures were negative. Although parainfluenza-3 virus was isolated from the lung tissue, immunohistochemistry (IHC) results were negative. The epidemiological context, pathological findings, and clinical signs were consistent with hypersensitivity pneumonitis, although its specific etiology could not be determined. Dairy production systems that utilize soil bedding may predispose animals to this condition, even though potential allergens were not assessed in this case. Nonetheless, this clinical and pathological presentation should be considered as a differential diagnosis for respiratory disease under similar production conditions.