MVSc

In the present study, the sero conversion to two doses of Brucella abortus strain RB51 vaccine was assessed in cattle. Interference of Brucella abortus strain RB51 with routine diagnostic tests for brucellosis was also compared with Brucella abortus strain 19 vaccine. Vaccinations were done in sero negative calves of four months and above age. The study animals were grouped into three. Animals of group I and II were subcutaneously vaccinated with 1.8×1010 CFU and 1×1010 CFU of Brucella abortus strain RB51 vaccine respectively. Whereas group III animals were vaccinated with 4×1010 CFU of Brucella abortus strain 19 subcutaneously. Immune responses were assessed at weekly interval during the first month and there after at monthly interval for a period of six months employing indirect Enzyme Linked Immunosorbent Assay (ELISA). Clinical observations of all animals were also made two days before and one week after vaccination.

All the vaccinated animals showed febrile reaction during the first 24 to 48hours post inoculation. But returned to normal temperature by 72 hours post inoculation. Eighty two per cent of the vaccinated animals developed swelling at the inoculation site 48 hours after vaccination but found to be reduced by 96 hours and became normal after one week. Animals were quite active and with good appetite throughout the observation period.

None of the Brucella abortus SRB51 vaccinated animals, both with higher or lower dose, produced detectable antibody response in the conventional serological tests viz., RBPT and STAT throughout the study period. Whereas animals vaccinated with Brucella abortus S19 produced detectable antibody responses in RBPT and STAT till 90th day.

Cattle vaccinated with higher dose of Brucella abortus SRB51 produced significant antibody level earlier (seventh day) than those with lower dose (21st day) and persisted longer (upto150 days), when compared to the group II (only upto 120 days). But both groups showed maximum immune response on the same observation period i.e on 60th day of vaccination. The proportion of animals with significant immune responses were also higher in animals vaccinated with higher dose than those with lower dose except on day 21 and day 90.

From the serologic point of view, it is concluded that Brucella abortus strain RB51 is an ideal vaccine candidate than Brucella abortus strain 19 and animals vaccinated with higher dose produced better immune response to Brucella abortus SRB51, when compared to those vaccinated with lower dose.