Vr. Lord et al., FIELD-STUDY OF VACCINATION OF CATTLE WITH BRUCELLA-ABORTUS STRAINS RB51 AND 19 UNDER HIGH AND LOW DISEASE PREVALENCE, American journal of veterinary research, 59(8), 1998, pp. 1016-1020
Objective-To assess humoral and protective immunity in cattle vaccinat
ed by 12 months with Brucella abortus vaccine strains RB51 and 19 unde
r field conditions of high and low brucellosis prevalence. Animals-450
seronegative female cattle: 330 three to eight months old (calves). a
nd 120 ten to twelve months old (heifers). Procedures-Ranch A had high
prevalence (39%) of brucellosis, and ranch B had low prevalence (2%),
as determined by results of conventional serologic testing: agar gel
immunodiffusion and the ring test. Seronegative cattle were vaccinated
once OF twice with 5 x 10(9) colony-forming units of B abortus strain
RB51 or once with strain 19. After vaccinating 285 cattle with strain
RB51 and 165 with strain 19, 74 (26%) and 30 (18%), respectively, wer
e bred to seropositive bulls, then were kept within the infected herd
of origin. Results-All cattle vaccinated with strain 19 seroconverted
30 days later. All 285 cattle vaccinated with strain RB51 had negative
results for all serologic tests, including agar gel immunodiffusion.
All RB51-vaccinated cattle that became pregnant had negative results f
or the ring test and for conventional serologic tests after their firs
t carving. Conclusions-Strain RB51 can be used as a live organism vacc
ine without inducing antibody titers that interfere with serodiagnosis
, and induced 100% protection against field strain B abortus-induced a
bortion in cattle vaccinated at least 1 year before mating to an infec
ted bull. Vaccination with strain 19 under similar conditions was less
effective than vaccination with strain RB51.