Bacterial and viral agents in cattle with and without respiratory signs in dairy herds from São Paulo and Rio Grande do Sul states, Brazil

ABSTRACT: Bovine respiratory disease is a multifactorial syndrome of complex etiology, involving interactions among bacterial and viral agents, and has a significant impact on the cattle industry worldwide. This study aimed to identify agents associated with respiratory infections in dairy herds in São Paulo (SP) and Rio Grande do Sul (RS) states. Nasal swabs obtained from animals with and without nasal/respiratory signs in 10 herds in SP (n = 178) and nine herds in RS (n = 273) were submitted to nucleic acid extraction and to endpoint multiplex reverse transcription polymerase chain reaction (RT-PCR)/PCR assays for bacterial and viral agents. The bacterial multiplex PCR covers four bacteria (Histophilus somni, Mannheimia haemolytica, Mycoplasma bovis and Pasteurella multocida); the viral multiplex encompasses seven viruses (bovine herpesvirus 1 - BoAHV-1; bovine viral diarrhea virus 1 and 2 - BVDV-1, BVDV-2; HoBi-like pestivirus - HoBiPeV; bovine respiratory syncytial virus - BRSV; bovine parainfluenza 3 virus - BPIV-3 and bovine coronavirus - BCoV). The overall frequency of positive samples was 23.7% (107/451) and the most frequently detected agents were H. somni (30.8%, 33/107) and M. bovis (21.5%, 23/107), followed by BCoV (19.6%, 21/107), BPIV-3 (13.1%, 14/107), M. haemolytica (11.2%, 12/107) and BRSV (9.3%, 10/107). Mixed infections were detected in 13.1% samples (14/107), especially involving bacteria of the Pasteurellaceae family, but also BCoV and BRSV. Considering herd prevalence, H. somni was detected in 57.9% herds (11/19), M. bovis in 52.6% (10/19), M. haemolytica in 42.1% (8/19), BPIV-3 in 36.8% (7/19), BCoV in 26.3% (5/19), BoAHV-1 and BRSV in 21% (4/19), P. multocida in 15.8% (3/19) and BVDV in 5.3% (1/19) herds. Overall, these results offer an overview of the main viral and bacterial agents associated with respiratory infection in dairy herds in the studied regions (SP and RS). In addition, the complex etiology of respiratory disease in cattle highlights the importance of employing multi-etiological diagnostic approaches for comprehensive and accurate investigation.