Safety and efficacy of a combined parapox/BVD vaccine.

The combination of a Bovine Viral Diarrhea-Mucosal Disease-attenuated vaccine strain with heat-inactivated parapoxvirus was tested with respect to safety and efficacy in mice, rabbits and fattening calves. The safety on this vaccine was guaranteed in mice and rabbits under laboratory conditions and in calves under field conditions. Laboratory investigations demonstrated a strong anti-BVD antibody response in rabbits compared to antibody formation after vaccination with the monovalent BVD-vaccine component. In mice the induction of high unspecific defence against heterologous viral challenge (VSV, Aujeszky) was possible only with the combined vaccine and the parapox (ORF) vaccine component. Two BVD-seronegative calves kept under isolated conditions showed high titers of BVD-neutralizing antibodies three weeks after a single vaccination with a three-fold vaccine dose. Leukopenia could not be detected in 13 randomly chosen BVD-seronegative calves on days 1, 2 and 4 after vaccination. In field trials each of the 69 (29%) BVD-seronegative calves developed high titers of BVD-neutralizing antibodies three weeks after a single (i.m.) inoculation. The same phenomenon occurred with animals which had low pre-vaccination BVD neutralizing antibodies, whereas the third group of calves with high prevaccination antibody titers had a moderate decrease in neutralizing antibodies within three weeks after vaccination. Mortality and morbidity rates in fattening farms decreased markedly after the experiment and during an observation period of one year. Improved immunological response of rabbits and cattle to a single vaccination with the combined parapox-BVD vaccine compared to a monospecific BVD vaccination was a result of immunomodulating effects of the parapox (ORF) vaccine component.