Comparison of the Subcutaneous and Conjunctival Route of Vaccination with Brucella abortus Strain 19 Vaccine in Adult Cattle

Abstract

Summary A dairy herd of approximately 700 animals in which brucellosis had not been eliminated by the test and slaughter method over a 5-year period was chosen for a field study to determine the effects of adult vaccination with strain 19 vaccine on reduction of infection and on serologic testing. The standard dose of vaccine administered by the subcutaneous ( sc ) route was compared with a reduced dose given 2 times via the conjunctiva (C). Forty percent of the herd was vaccinated by each method and 20% was not vaccinated. Serum samples obtained at approximately 2-month intervals were subjected to 5 serologic tests, and selected cattle were examined bacteriologically. Animals considered to be infected with field strains of Brucella abortus were removed. All serologic and bacteriologic data for a 13-month observation period were entered into a computer file and analyzed. The sc method of vaccination, using a dose containing 9 × 10 10 viable brucellae, caused a prolonged serologic response, which required complement-fixation testing and milk culture to identify infected animals. In contrast, the C method, using a reduced dose (4.5 × 10 9 viable brucellae) given twice, did not interfere with serologic testing. There was no indication that the latter method provided any less protection than that provided by the standard method. Reduction in the rate of infection was achieved within 6 months, but the presence of nonvaccinated animals as well as continued addition of purchased replacements contributed to the persistence of infection. Five serologic tests were evaluated for their efficacy in this herd. The standard tube test was the least sensitive test; the card test was the most sensitive test but lacked specificity in vaccinated animals. The complement-fixation test performed somewhat better than the rivanol test in the C and nonvaccinated groups, whereas the rivanol test was better in the sc group.