Effects of challenge dose on the clinical and immune responses of cattle vaccinated with reduced doses of Brucella abortus strain 19.

Fifty-seven pregnant beef heifers that were unvaccinated or previously vaccinated with Brucella abortus S19, at a dose of either 10(9) or 10(10) colony-forming units (CFU), were challenge-exposed intraconjunctivally with virulent B. abortus S2308 at a dose of 9.4 X 10(6) CFU (Experiment 1) or 5.2 X 10(7) CFU (Experiment 2). In Experiment 1, S19 afforded significant protection (P less than 0.01) against challenge exposure in that 8 of 9 unvaccinated heifers, 1 of 11 vaccinated with 10(9) CFU, and 3 of 10 vaccinated with 10(10) CFU aborted or delivered weak, non-viable calves. In Experiment 2, vaccination did not afford significant protection (P greater than 0.05) in that 9 of 9 unvaccinated heifers, 8 of 10 vaccinated with 10(9) CFU, and 8 of 8 vaccinated with 10(10) CFU aborted. Serologic responses to B. abortus were determined by three standard tests, as well as a quantitative fluorometric immunoassay (FIAX) and an enzyme-linked immunosorbent assay. In Experiment 1, the early serologic response, 0-8 weeks after challenge, appeared greater for controls than for vaccinates, but in Experiment 2, the early response, 0-6 weeks after challenge exposure, appeared greater for vaccinates than for controls. The lymphocyte blast transformation assay, using heat-killed B. abortus as an antigen, was performed sequentially after challenge exposure. In general, mean responses were significantly higher (P less than 0.05) for vaccinated than for non-vaccinated heifers. For individual heifers, an association could not be established between the lymphocyte blast transformation assay and the clinical response to challenge exposure.

Transient enhancement of the serum antibody response to Brucella abortus strain 19 in cattle treated with levamisole.

Two experiments were done on 57 steers. These cattle were allotted to 8 groups (4 groups/experiment) and vaccinated with 1 to 3 X 10(9) colony-forming units of Brucella abortus strain 19. Cattle in 3 of the 4 groups/experiment were given 6 mg of levamisole/kg, subcutaneously, either at the time of vaccination (day 0), 7 days later, or at both times. Serum antibody titers to B abortus were measured sequentially for 28 days in experiment 1 and for 56 days in experiment 2, using the card test, Rivanol test, complement-fixation test, fluorometric immunoassay, and an enzyme-linked immunosorbent assay. In general, the highest mean antibody titers, as determined by all serologic tests, occurred in steers treated with levamisole at 7 days after vaccination or in those treated at the time of vaccination and 7 days later. By the card test on day 56, there was a significantly (P less than 0.05) greater number of seropositive cattle among those given levamisole 7 days after seropositive cattle among those given strain 19 alone. Simultaneous administration of strain 19 and levamisole did not alter antibody responses to B abortus.

Effect of oxytetracycline administration on antibody response to Brucella abortus vaccination in calves.

In 5- to 7-month-old dairy calves, concurrent oxytetracycline administration and subcutaneous vaccination with 10(9) Brucella abortus strain 19 organisms reduced the percentage of animals with detectable humoral antibodies to Brucella abortus, when compared with untreated vaccinated calves of the same age range. The reduction of antibody reaction in the card test was less than that associated with the injection of 10(9) heat-killed Brucella abortus strain 19 organisms.