EXPERIMENTAL USE OF A DOT-BLOT ASSAY TO MEASURE SEROLOGIC RESPONSES OF CATTLE VACCINATED WITH BRUCELLA-ABORTUS STRAIN RB51

Brucella abortus strain RB51 was recently approved as an official bruc ellosis calfhood vaccine for cattle by the Animal and Plant Health Ins pection Service branch of the United States Department of Agriculture. Currently available serologic surveillance tests for B. abortus do no t detect seroconversion following SRB51 vaccination. The purpose of th is study was to evaluate a dot-blot assay using gamma-irradiated strai n RB51 bacteria for its specificity and sensitivity to detect antibody responses of cattle vaccinated with strain RB51. Dot-blot titers of s era at a recommended dosage (10(10) colony-forming units) were similar to those of sera from cattle vaccinated with similar numbers of B. ab ortus strain 19 and greater (P < 0.05) than titers of nonvaccinated ca ttle. In the first 12 weeks after vaccination with 10(10) colony-formi ng units of strain RB51, the RB51 dot-blot assay had 100% specificity for titers of 80 or less and a 53% sensitivity for titers of 160 or gr eater. Sensitivity of the RB51 dot-blot assay peaked at 4 weeks after vaccination with 10(10) colony-forming units of strain RB51. Dot-blot responses of sera from cattle vaccinated with a reduced dosage of stra in RB51 (10(9) colony-forming units) did not differ (P > 0.05) from ti ters of sera from nonvaccinated cattle. Following intraconjunctival ch allenge with B. abortus strain 2308, titers on the RB51. dot-blot assa y did not differ (P > 0.05) between nonvaccinated cattle and cattle va ccinated at calfhood with strain 19 or strain RB51.