PSIX-14 - Active and passive immunity in calves vaccinated with a subunit targeted vaccine against BVDV

Abstract: Bovine viral diarrhea virus (BVDV) infects ruminants, with a worldwide distribution, the virus causes a broad spectrum of clinical diseases and economic losses. Vaccination against BVDV is an important component of prevention and control programs. Currently, only modified live vaccines (MLV) and inactivated vaccines are used. Both have historical disadvantages; MLV in terms of safety and inactivated vaccines in terms of immunogenicity. We have previously reported the development and efficacy trials of the first targeted subunit vaccine against BVDV. The core of the vaccine is a fusion of the BVDV structural protein, E2, to a single-chain antibody, APCH, together termed, APCH-E2. The APCH antibody targets the E2 antigen to the MHC-II present on antigen-presenting cells. The goal of this work was to evaluate passive immunity through colostrum and active immunity of calves immunized with the novel vaccine. 24 A. angus heifers were divided into two groups, 12 immunized with the vaccine and 12 received placebo, in the last trimester of gestation. Serum samples from calves were taken at day 30 of age and analyzed by competitive ELISA. In the vaccinated group, 92% of the d30 old calves maintained medium (25%) or high (67%) antibody levels against BVDV, while 50% of the animals in the control group presented low antibody level (Pearson's chi-squared p:0,07) (Table 1).

At 5 months of age, calves of both groups were immunized with the targeted vaccine. Thirty days later, 96% of the calves had medium or high antibody levels against BVDV, which was independent of their respective heifer vaccine status.

These results confirm the new targeted subunit vaccine against BVDV is safe and efficacious to be used in pregnant cattle and can passively immunize newborn calves. They also show that these maternal antibodies do not interfere with the active immunization of calves.