SAFETY AND IMMUNOGENICITY OF BRUCELLA-ABORTUS STRAIN RB51 VACCINE IN PREGNANT CATTLE

Objective-To determine the safety and immunogenicity of Brucella abort us strain RB51 as a vaccine in pregnant cattle. Animals-12 Polled Here ford heifers obtained from a brucellosis-free herd and bred on site at 16 months of age to a brucellosis-free bull. Procedure-Pregnant heife rs were vaccinated at 6 months' gestation with 10(9) colony-forming un its of B abortus strain RB51 (n = 5), 3 x 10(8) colony-forming units o f B abortus strain 19 (n = 5), or sterile pyrogen-free saline solution (n = 2). Samples were periodically collected for serologic testing an d lymphocyte blastogenesis assays. At full gestation, heifers were eut hanatized and specimens were collected for bacteriologic culture, hist ologic analysis, and lymphocyte blastogenesis assay, using various ant igenic stimuli. Results-None of the strain RB51- or strain 19-vaccinat es aborted or had gross or microscopic lesions at necropsy that were c onsistent with brucellosis. Maternal blood mononuclear cells from stra in RB51- and strain 19-vaccinates had proliferative responses to gamma -irradiated strain RB51 and strain 19 that were greater than responses by cells from nonvaccinated controls. In contrast, maternal superfici al cervical lymph node cells from strain 19-vaccinates had proliferati ve responses to gamma-irradiated strain RB51 or strain 19 bacteria gre ater than those of cells from RB51-vaccinates and nonvaccinated contro ls. None of the heifers vaccinated with strain RB51 developed antibodi es detected by use of the standard tube agglutination test, but all de veloped antibodies to strain RB51 that reacted in a dot ELISA, using i rradiated strain RB51 as antigen. Conclusions-Pregnant cattle can be s afely vaccinated with strain RB51 without subsequent abortion or place ntitis. Furthermore, strain RB51 is immunogenic in pregnant cattle, re sulting in humoral and cell-mediated immune responses, but does not in terfere with serologic diagnosis of field infections.