In vitro neutralization of HoBi-like viruses by antibodies in serum of cattle immunized with inactivated or modified live vaccines of bovine viral diarrhea viruses 1 and 2.

HoBi-like viruses are an emerging species of pestiviruses with genetic and antigenic similarities to bovine viral diarrhea viruses 1 and 2 (BVDV1 and BVDV2). Vaccines for HoBi-like viruses are not yet available. However, both modified live virus (MLV) and killed virus (KV) vaccines against BVDV are widely used worldwide. This study evaluated the cross reactive antibody response against HoBi-like pestiviruses in sera of cattle immunized with BVDV1 and BVDV2 vaccines. Groups "KV" and "MLV", with 25 calves each, received killed or modified live vaccines, respectively, containing both BVDV1 and BVDV2 antigens. The antibody response was evaluated by virus neutralization test. The average of geometric mean titers (GMTs) of neutralizing antibodies in serum against HoBi-like viruses in the MLV group was 12.9, whereas GMTs to BVDV1, BVDV2 and border disease virus (BDV) were 51.1, 23.5, and 12.4, respectively. In this group, neutralizing antibodies against BVDV1, BVDV2, HoBi-like viruses and BDV were detected in 100%, 94%, 68% and 68% of calves, respectively. The GMT of neutralizing antibodies in serum against BVDV1, BVDV2, HoBi-like viruses and BDV in the KV group were 24.7, 14.5, 10.4 and 11, respectively. Similarly, the percentage of animals with neutralizing antibodies against BVDV1, BVDV2, HoBi-like viruses and BDV were 84%, 56%, 34% and 44%, respectively. These results indicate that MLV or killed BVDV1 and BVDV2 vaccines induce a cross reactive antibody response comparatively weak to HoBi-like viruses, and this response would likely not suffice to confer protection.