Clinical and immunologic responses of vaccinated and unvaccinated calves to infection with a virulent type-II isolate of bovine viral diarrhea virus
Cortese, V.S.; West, K.H.; Hassard, L.E.; Carman, S.; Ellis, J.A.
Journal of the American Veterinary Medical Association 213(9): 1312-1319
1998
ISSN/ISBN: 0003-1488 PMID: 9810390 Document Number: 235
Objective-To determine efficacy of a modified-live type-I isolate of bovine viral diarrhea virus (BVDV) vaccine in protecting calves from infection with a virulent type-II isolate, and to determine which type of immune response (ie, humoral or cellular) correlates with protection. Design-Prospective study. Animals-28 neonatal Holstein and Holstein-cross calves. Procedure-Within 18 hours of birth, calves received maternal colostrum or were fed pooled colostrum. On days 7 to 10 after birth, calves were determined to be seropositive (n = 16) or seronegative (12) for antibodies to BVDV on the basis of ELISA and virus neutralization test results. Seropositive and seronegative 10- to 14-day-old calves were then given a combined vaccine that contained a modified-live type-I isolate of BVDV or a similar vaccine that lacked protection against bovine viral diarrhea. All calves were inoculated intranasally approximately 21 days after vaccination with a virulent type-II isolate of BVDV. Clinical and immunologic variables, including clinical scores, rectal temperatures, results of CBC with lymphocyte subset analysis, antibody responses, and cell-mediated immune responses, were monitored for 14 days after inoculation. Results-Seronegative-unvaccinated calves developed severe disease and required euthanasia. Vaccination of seronegative calves with a modified-live type-I isolate had a disease-sparing effect as did passive transfer of colostral antibodies to BVDV. Clinical scores were not significantly different between seropositive-vaccinated and seropositive-unvaccinated calves after viral inoculation. Clinical Implications-A single dose of a modified-live type-I isolate of BVDV vaccine protects young calves from clinical signs of disease associated with type-II isolates.
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