Bovine respiratory disease associated with Histophilus somni and bovine respiratory syncytial virus in a beef cattle feedlot from Southeastern Brazil

Abstract

Bovine respiratory disease (BRD) is a complex multifactorial and multi-etiological disease entity that is responsible for the morbidity and mortality particularly in feedlot cattle from North America. Information relative to the occurrence of BRD in Brazil and the associated infectious agents are lacking. This study investigated the participation of infectious agents of BRD in a beef cattle feedlot from Southeastern Brazil. Nasopharyngeal swabs of 11% (10/90) of cattle (n, 450) with clinical manifestations of respiratory distress were analyzed by targeting specific genes of the principal infectious pathogens of BRD. In addition, pulmonary fragments of one the animals that died were collected for histopathological and molecular diagnoses. The nucleic acids of Histophilus somni and bovine respiratory syncytial virus (BRSV) were identified in 20% (2/10) of the nasopharyngeal swabs of the animals with respiratory distress; another contained only BRSV RNA. Moreover, the nucleic acids of both infectious agents were amplified from the pulmonary fragments of the animal that died with histopathological evidence of bronchopneumonia and interstitial pneumonia; the nasopharyngeal swab of this animal also contained the nucleic acids of both pathogens. Additionally, all PCR and/or RT-PCR assays designed to detect the specific genes of Mannheimia haemolytica, Pasteurella multocida, Mycoplasma bovis, bovine viral diarrhea virus, bovine herpesvirus -1, bovine parainfluenza virus-3, and bovine coronavirus yielded negative results. Phylogenetic analyses suggest that the isolates of H. somni circulating in Brazil are similar to those identified elsewhere, while there seem to be diversity between the isolates of BRSV within cattle herds from different geographical locations of Brazil.