The aim,of the study was to determine the cross protection against a challenge infection with a highly virulent BVDV2-strain (strain 890) after a single vaccination with a BVDV1 live vaccine (Vacoviron((R))/Mucosiffa((R))) or a repeated vaccination with a BVDV1 inactivated vaccine (Mucobovin((R))). Fifteen calves were allotted into one control- and two vaccine groups. The Mucobovin((R))-group was vaccinated at days 61 and 29, and the Vacoviron((R))-group at day 61 before challenge infection. The calves were monitored by clinical observation using the point-scheme of Cortese (behaviour, haemorrhages, respiratory symptoms and diarrhoea), and by haematological (leukocyte and platelet count), virological (virus isolation in cell culture and RT-PCR) and serological parameters. The animals vaccinated with the live vaccine displayed the best immunity of the three groups. The Mucobovin((R)) group also developed immunity, but clinical signs were more pronounced than in the Vacoviron((R)) group. The control group exhibited significant clinical changes in contrast to the vaccine groups. Four of the five control animals and one calf in the Mucobovin((R))-group were leukopenic. After the challenge infection, virus was only isolated from the control animals. RT-PCR was positive on 20 samples (over a 12 days period) in the con- trol-group, and in six samples (over a five days period) in the Mucobovin((R)) group and remained negative in the Vacoviron((R)) vaccinated animals. The control animals sero-converted after the challenge infection, the Mucobovin((R)) group after the second vaccination and the Vacoviron((R)) animals after the single vaccination. Antibody-titers in all groups increased markedly after the challenge infection. The study shows that the vaccination with a BVDV1 vaccine can produce an adequate protection against a BVDV2 infection.
