Clinical and immunologic responses of cattle to vaccinal and natural bovine virus diarrhea virus (BVDV)
Cortese, Victor Stuart
This research had two objectives. First, to determine if BVDV vaccines containing type I BVDV were safe and efficacious against a type II BVDV challenge in calves. Second, to determine if modified live BVDV vaccines could stimulate a greater degree of protection against BVDV reproductive syndromes as well as a longer duration of cross neutralizing antibodies than the current inactivated vaccines. One to nine week old calves were administered modified live and/or inactivated BVDV containing vaccines on various schedules. The calves were monitored for adverse effects and followed serologically for 12 weeks. BVDV challenge studies were performed in calves vaccinated with either a modified live or inactivated vaccine beginning on day 14 of age. BVDV sero-negative and sero-positive calves were included in the study. Studies were performed in BVDV sero-negative cows. Safety was determined by assessing the risk of BVDV transmission of vaccinal virus. Duration of cross neutralizing antibodies stimulated by a single modified live BVDV vaccine was determined. Finally, the ability of a modified live BVDV vaccine to provide fetal protection was assessed. 'Results'. Neither the modified live BVDV vaccines nor the inactivated BVDV vaccine used in these studies caused adverse reactions in the young calves. Calves with BVDV maternal antibody less than 1:64 by virus neutralization testing responded to BVDV vaccination. Calves vaccinated with modified live BVDV vaccine or with high maternal antibody against BVDV were protected from a type II BVDV challenge. Inactivated BVDV vaccine conferred only partial protection against the challenge. Cows vaccinated with one of two modified live, NADL-containing, BVDV vaccines did not transmit measurable BVDV to contact control animals. One of these vaccines, following a single dose, produced antibodies that neutralized 12 isolates of BVDV that were still detectable 18 months after vaccination. This vaccine conferred 82% fetal protection against a challenge of virulent BVDV. This research serves to define the responses and protection produced by modified live vaccines and further demonstrates that modified live BVDV vaccines can stimulate a higher degree of protection than an inactivated BVDV vaccine.