Cross-protective efficacy of a bovine viral diarrhea virus (BVDV) type 1 vaccine against BVDV type 2 challenge.

A new genotype of bovine viral diarrhea virus (BVDV), designated BVDV type 2 (BVDV 2), has become prevalent in the field. BVDV 2 strains are antigenically distinct from currently available vaccine strains of the BVDV 1 genotype, raising concerns about cross-protection of these vaccines against BVDV 2 challenge. To determine cross-protective efficacy of a modified-live virus (MLV) vaccine containing BVDV 1 strain WRL (BVDV 1(WRL)), two studies were conducted in which the relative magnitude and duration of BVDV 1- and BVDV 2-specific serologic responses and protection against BVDV 2 challenge were determined. For the first study, 27 heifers were vaccinated (13 i.m. and 14 s.c.), while 13 heifers received negative control vaccine. Serum from the vaccinated heifers neutralized both BVDV 1 and BVDV 2 strains. The evolution and duration of BVDV 1 and BVDV 2 serologic responses were comparable, and antibody titers to BVDV 2 persisted through at least 105 days post-single vaccination. In a second, separate study, 17 calves were vaccinated (9 i.m. and 8 s.c.), and 11 calves were held as unvaccinated controls. Approximately seven months following vaccination, the calves were challenged intranasally with the 890 isolate of BVDV 2. Clinical signs of disease and fever were significantly reduced in vaccinates in comparison with controls. Vaccination eliminated nasal virus shedding in 87% of cattle and completely prevented viremia and leukopenia. These data indicate utility of BVDV 1(WRL) MLV vaccine in stimulation of long-term BVDV 2-specific serologic responses, protection against BVDV 2 challenge and reduction or elimination of virus shedding which can contribute to spread of BVDV 2 in herds.