A novel killed oil adjuvanted bovine viral diarrhea virus vaccine protects from viremia and clinical manifestations: an immune response and challenge study in cattle.

Bovine viral diarrhea virus continues to threaten animal health with serious economic losses worldwide. Various killed, live-modified, or recombinant vaccine strategies are being developed for protection and control against this virus. The most important thing discovered is the choice of local and widespread strains in the vaccine content. In this study, the effectiveness of a Montanide ISA 206 adjuvanted killed trivalent vaccine containing endemic local strains (TR-21 [BVDV-1l], TR-26 [BVDV-1f], and TR-15 [BVDV-2b]) isolated from Türkiye, was evaluated with a cattle challenge study. Experimental groups were designed as single dose vaccination (Group-I, n:11), two dose vaccination (Group-II, n:11), and unvaccinated (Group-III, n:6) with male calves aged about 6 months. Following the immunization, challenge virus (TR-72 [BVDV-1l], TCID 10) was given intranasally to each group (5 animals in Group-I and II and 4 animals in Group-III), and clinical findings, hematological changes, virus shedding, side effects, and viremia were monitored for 14 days after inoculation. Serological monitoring of the remaining animals against homologous and heterologous strains was carried out at one-month intervals between the 21st and 201st days after the first vaccination. The obtained results showed that the viremia, hematological changes, and clinical findings shown in unvaccinated animals (Group-III) were significantly suppressed (p < 0.05) in the vaccinated groups (Group-I and II). In addition, it was found that serologically monitored animals maintained protective neutralizing antibody (nAb) titers ≥ 8 log for vaccinal and also for all reference BVDV-1 strains, which is more than three-fold protective antibody response, lasting more than 7 months after the first vaccination, whether in single or two dose application. The rise of nAbs was also detected for heterogous BVDV strains. The detected nAb titers were significantly higher (p < 0.05) in the two dose vaccination group. Based on the results, it was concluded that this trivalent- inactivated vaccine candidate can protect cattle against acute BVDV infections.