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.
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).
Overall, the multiplex qPCR BRDC panel should be a rapid and accurate testing tool for diagnosticians in investigating BRDC cases and aid bovine practitioners to intervene BRDC in its early stages. Due to the quantitative nature of the panel, it can be used for epidemiological studies and proactive monitoring of cattle for respiratory disease problem. In addition to the BRDC qPCR panel, additional qPCR assays for B. trehalosi and BPIV-3 have also developed to aid BRDC investigation.
Preferred antemortem samples for the BRDC panel testing are tracheal washes and airway swabs. Tracheal washes can also be used for cytologic assessment of inflammatory process, in addition to differential diagnostics for microorganisms. Sampling procedure can be viewed at ISU-VDL website: http://vetmed.iastate.edu/vdpam/disease-topics/antemortem-respiratory-diagnostics.
When nasal swabs are collected, deep swabs (i.e., nasopharyngeal) are preferred. A guarded mare uterine swab can be used to obtain samples from the deep pharyngeal area. Swabs should be put in snap-cap or red-top tubes with a small amount (<1ml) of physiological saline without preservative to keep the swab tip damp, and be submitted on ice. Swabs can be pooled for testing.
Practitioners should be mindful that test results on swabs can be impacted by the use of intranasal vaccines. For further inquiries, contact diagnosticians at the Iowa State University Veterinary Laboratory.
Kyoung-Jin Yoon DVM, PhD, Dipl. ACVM, is with the Veterinary Diagnostic Laboratory/Veterinary Medical Research Institute, College of Veterinary medicine, Iowa State University.