SEROLOGIC RESPONSES OF BRUCELLA-ABORTUS STRAIN-19 CALFHOOD-VACCINATEDCATTLE FOLLOWING ADULT VACCINATION WITH STRAIN RB51

This study was designed to determine if Brucella abortus strain RB51, which expresses small amounts of the lipopolysaccharide O side chain, would cause positive responses on brucellosis serologic surveillance t ests when given to adult cattle that were vaccinated as calves with B. abortus strain 19. Cattle vaccinated as adults with strain RB51 that had been vaccinated as calves with strain 19 (n = 40) had significantl y greater antibody titers (P < 0.05) against strain RB51 at 4 and 8 we eks postvaccination in the dot blot assay than did animals (n = 10) no t vaccinated with strain RB51. When evaluated using the card or buffer ed acid plate agglutination presumptive tests, 7 strain RB51 vaccinate s tested positive at either 4 or 8 weeks following vaccination as comp ared with 4 cattle in the control group that were not vaccinated with strain RB51. One strain RB51 vaccinate was scored as suspect on the st andard tube agglutination (STA) test at 8 weeks following vaccination. Remaining samples from strain RB51 vaccinates tested negative on the STA, complement fixation (CF), rivanol, and particle concentration flu orescence immunoassay (PCFIA) confirmatory tests. Samples from 2 contr ol cattle were PCFIA positive at time 0; 1 of these animals was CF pos itive throughout the study. This study suggests that use of strain RB5 1 in cattle vaccinated with strain 19 as calves will not cause positiv e responses on confirmatory tests and will not impair brucellosis sero logic surveillance efforts.