Involvement of microbial respiratory pathogens in acute interstitial pneumonia in feedlot cattle

Objective-To evaluate viral and bacterial respiratory pathogens and Mycopla sma spp Isolated from lung tissues of cattle with acute interstitial pneumo nia (AIP) and cattle that had died as a result of other causes. Sample Population-186 samples of lung tissues collected from cattle housed in 14 feedlots in the western United States. Procedure-Lung tissues were collected during routine postmortem examination and submitted for histologic, microbiologic, and toxicologic examinations. Histologic diagnoses were categorized for AIR bronchopneumonia (BP), contr ol samples (no evidence of disease), and other disorders. Results-Cattle affected with AIP had been in feedlots for a mean of 1272 da ys before death, which was longer than cattle with BP and control cattle. D etection of a viral respiratory pathogen (eg, bovine respiratory syncytial virus [BRSV], bovine viral diarrhea virus, bovine herpesvirus 1, or parainf luenza virus 3) was not associated with histologic category of lung tissues . Bovine respiratory syncytial virus was detected in 8.3% of AIP samples an d 24.0% of control samples. Histologic category was associated with isolati on of an aerobic bacterial agent and Mycoplasma spp. Cattle with BP were at greatest risk for isolation of an aerobic bacterial agent and Mycoplasma s pp. Conclusions and Clinical Relevance-Analysis of these results suggests that AIP in feedlot cattle is not a consequence of infection with BRSV. The Incr eased risk of isolation of an aerobic bacterial agent from cattle with AIR compared with control cattle, may indicate a causal role or an opportunisti c infection that follows development of AIP.