Prophylactic and Therapeutic Efficacy of a Glycoconjugate Vaccine Against Bovine Brucellosis

Bovine brucellosis is a zoonotic disease. It impacts dairy industry since it is a major cause of abortion. The disease is caused by bacteria belonging to the genus Brucella. The pathogen is excreted in milk, semen and aborted materials. Bovine brucellosis is currently controlled by calfhood vaccination of females using live attenuated B. abortus strains (S19/RB51), however it does not provide 100% protection, and its use is restricted by age and gender. The vaccine strains are infectious to humans. Review of literature indicated that use of glyco-conjugate (GC) vaccines could address the above problems. Therefore, the objective of study was to assess the protective efficacy and therapeutic potential of GC vaccine prepared from Brucella abortus S19 (S19GC) in cattle. Immunization of Brucella free animals with two doses of 50μg each at an interval of 90 days by sub-cutaneous route resulted in pronounced Th1 mediated interferon gamma (IFN-γ) response (P=0.0061) as observed in ELISPOT assay compared to unvaccinated controls till 90 days post vaccination (DPV). The ability of S19GC to arrest shedding of Brucella was studied in brucellosis positive animals, vaccination of infected animals each with 50μg of S19GC by subcutaneous route resulted in arresting of shedding as evidenced by negative culture results, reduction (2 log folds) in genome copy number as observed by realtime PCR (qPCR). The prime-boost strategy of immunization (50 μg dose/cattle) of a group of cattle infected with brucellosis (> 53%) was only able to arrest bacterial shedding transiently (7–60 DPV) in 66.67% immunized cattle, and after booster bacterial shedding was not recorded by culture in 83.34% of the animal till 250 PI. Also, Brucella genome was not detected transiently (7–150 DPV) in samples; but was detected thereafter till 250 DPV. The most promising effect of immunization with S19GC was observed in a group of cattle with a mixed population of brucellosis negative and positive animals of the above farm. Immunization of this group of animals with 100 ?g of S19GC resulted in complete stoppage of shedding as indicated by culture and qPCR. The post immunization anti-LPS and anti-OMP antibody IgG1 and IgG2 response differed (P<0.01) at 30 DPV compared to pre immunization, suggesting the involvement of both Th2 and Th1 cells in the immunity conferred by S19GC vaccine.