Evaluation of a modified live virus type-1a bovine viral diarrhea virus vaccine (Singer strain) against a type-2 (Strain 890) challenge

Both type-1 and type-2 bovine viral diarrhea virus (BVDV) infections are responsible for major losses in the cattle industry. However, several commercial BVDV vaccines contain only a type-1 strain. A vaccine trial was conducted to evaluate the efficacy of BVDV type-1 (Singer strain; BVDV-1) vaccine for protecting calves challenged with virulent BVDV type-2 (890 strain; BVDV-2). Thirty-eight BVDV-negative calves were randomly allocated to four groups. One group was treated with a modified live virus (MLV) BVDV-1 vaccine by IM injection and another group was treated with the same vaccine by SC injection. Two groups served as nonvaccinated controls (one IM and one SC). Twenty-eight days following vaccination, the calves were challenged with BVDV-2 and monitored for 21 days. Clinical scores and body temperatures of vaccinated calves were significantly (P <.05) lower than for controls on several days, and peak differences occurred 8 days after challenge. The control calves had significantly (P <.05) lower leukocyte counts 3 through 8 days after challenge; leukocyte counts for vaccinated animals did not decline significantly from prechallenge levels. There were no differences in protection between the IM and SC routes of vaccination. The study demonstrated satisfactory cross protection of the BVDV-I vaccine against BVDV-2 challenge.