Despite advances in the development of vaccines, pharmaceuticals and disease management systems, bovine respiratory disease complex (BRDC) continues as the major disease compromising health within the cattle industry.
Preferred antemortem samples for the BRDC panel testing are tracheal washes and airway swabs. The annual economic loss associated with BRDC in the U.S. cattle industry has been estimated at 1 billion dollars due to the loss of cattle productivity (e.g., decreased milk production, delayed weight gain, reduced carcass value), increased labor expenses and drug costs, and death loss of affected animals.
Multiple infectious agents contribute to BRDC. The major infectious agents include bovine herpesvirus 1 (BoHV-1), bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), bovine coronavirus (BCoV) and bovine parainfluenza virus 3 (BPIV-3), Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Mycoplasma bovis. More recently, Bibersteinia trehalosi has been postulated as a potential infec tious agent for BRDC. Since the pathogens described above are individually or concurrently involved in the development of BRDC, the rapid and reliable detection of these pathogens in a differential manner is important for implementing effective treatment and preventive strategies in a timely manner.
New antemortem/postmortem assays
Recently Iowa State University Veterinary Diagnostic Laboratory (ISUVDL) has developed a panel of two multiplex quantitative real-time PCR (qPCR) assays which can simultaneously detect eight BRDC pathogens (BoHV-1, BRSV, BCoV, BVDV, M. bovis, M. haemolytica, H. somni, and P. multocida) in antemortem (tracheal wash, airway swab, nasal swab) and postmortem (lung, bronchioalveolar lavage, bronchial swab) samples in a quantitative manner.
The estimated analytical sensitivity of the panel is less than 10 TCID50/ml and 200 CFU/ml for the viral and bacterial targets, respectively. Testing conducted on approximately 200 clinical samples procured from BRDC submissions to diagnostic laboratories in Iowa and Texas showed that the panel simultaneously detected the target pathogens without cross reactivity in less time and at lower cost than laboratory routine tests. The test agreement between the panel and each laboratory’s routine tests was 82%-100%. The discrepant results were mostly due to samples that were tested positive by the panel but negative by the routine tests (i.e., the panel is more sensitive than the routine tests).