Submitted to: American Journal of Veterinary Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/1998
Publication Date: N/A
Citation: Interpretive Summary: Bovine viral diarrhea virus (BVDV) is a widespread viral pathogen of cattle. The virus induces a variety of diseases that include abortion and reproductive failure, pneumonia, diarrhea, and sudden death. Available vaccines for BVDV contain either inactivated or modified-live virus. Currently, vaccines for BVDV are granted licensure if they protect challenge-exposed vaccinated cattle from developing fever, diarrhea, respiratory disease, and leukopenia (low number of white blood cells). However, one of the most common disease manifestations induced by BVDV is reproductive failure caused by fetal infection with the virus. For licensure, vaccines are not required to confer protection to the fetus. Further, the available literature on fetal protection following vaccination of the dam is almost nonexistent. A preliminary investigation was conducted in which 12 open cows were vaccinated with a modified-live virus vaccine and then bred about 6 weeks after vaccination. At 70 to 75 days after breeding, the cows were challenge-exposed with BVDV. The vaccine conferred protection to the fetus in 10 of 12 vaccinated cows. In contrast, virus infected the fetus in 6 of 6 nonvaccinated cows. This is the first controlled study on the efficacy of modified-live virus vaccine for fetal protection. From this study, it appears the current modified-live virus vaccines for BVDV are at least partially protective for the fetus. The information provided by the study is valuable to beef and dairy producers, veterinary clinicians and diagnosticians, and veterinary biologics manufacturers.
Technical Abstract: To determine the efficacy of a vaccine containing modified-live bovine virus diarrhea virus (BVDV) type I in protecting cows from in utero infection and disease of the fetus with an isolate of a virulent heterologous BVDV type I. The design was a blinded controlled challenge study. Eighteen BVDV seronegative and virus isolation negative, yearling beef heifers were selected for this study. Cattle were then randomly assigned to either control (unvaccinated, n=6) or BVDV modified-live vaccinated (n=12) test groups. Twelve heifers were administered a combination vaccine containing a modified-live BVDV comprised of a type I cytopathic (NADL) strain. All 18 heifers were then naturally bred and then challenged, intranasally, between 70-75 days of gestation, with a BVDV type I, and the pregnancies were followed and the persistent infection status of the offspring was determined after calving. Antibody levels of the vaccinated and control heifers were also monitored. All six of the calves born from the control heifers had multiple positive virus isolations and were diagnosed as persistently infected. In comparison, only 2 of the calves from vaccinated cows were virus isolation positive and were determined to be persistently infected. One vaccinated cow aborted but the fetus was determined to be not persistently infected and the abortion was not due to a BVDV infection. These data indicate that a single dose of a modified-live, NADL ved BVDV vaccine will confer fetal protection against a heterologous BVDV challenge.