Methods of antemortem sampling for identification of microbial agents in bovine respiratory disease (BRD)

Abstract

Although bovine respiratory disease (BRD) can often be managed satisfactorily without diagnosis of microbial agents, when presumptive management is unsuccessful, identification of viruses or bacteria may reveal unexpected contributors, or agents for which a change in vaccination strategy or antimicrobial may be appropriate. The most common and feasible techniques for field use include nasal swabs, guarded nasopharyngeal swabs (NPS), transtracheal aspiration, and non-endoscopic bronchoalveolar lavage (BAL). Nasal swabs or NPS are ideal for rapidly sampling large numbers of cattle; evidence suggests that testing these for viruses or bacteria reliably represents the agents in the lower respiratory tract at the group level. If only 1 or a small number of animals are to be sampled, the tracheal aspirate or BAL may provide a more reliable result. Recent vaccination with modified-live viral (MLV) vaccines can cause false positive results by any method, thus sampling should not be carried out within 1 month of MLV vaccination. Paired serology can be useful for diagnosis of viral agents, but serologic tests for bacterial BRD agents are not readily available in diagnostic laboratories. Paired serology can be difficult to interpret in calves with maternal antibody, or in recently vaccinated cattle.