BOVINE RESPIRATORY-TRACT DISEASE CAUSED BY BOVINE VIRAL DIARRHEA VIRUS

Although several viruses and bacteria are capable of inducing bovine r espiratory tract disease, a pivotal organism in the cause of this comp lex disease may be bovine viral diarrhea virus (BVDV). Circumstantial evidence has long supported this hypothesis. It is frequently present in diseased respiratory tract tissues often together with other viruse s or bacteria. Field observations suggest marked synergism occurs. Res earchers have confirmed that, in most instances, the virus itself elic its only a mild respiratory tract disease in susceptible calves, but s ome strains may be much more pneumo-pathogenic than others. Experiment al evidence now supports the hypothesis, that BVDV markedly enhances r espiratory tract disease caused by IBRV, BRSV, or Pnsteurella haemolyt ica; that it impairs pulmonary immunity; and that it, by itself, may p roduce mild respiratory tract disease.