Abstract:
The effective control and eradication of brucellosis in developing countries
can be achieved by quick and accurate diagnosis and effective vaccination.
Protective efficacy of existing vaccines as well as diagnostic accuracies of various
serological tests have not been thoroughly studied and verified in buffaloes, the
prime dairy animal of South Asia. In the Present studies Brucella abortus strain 19
(S19) and strain RB51 (SRB51) vaccines were tested for inducing humoral and cell
mediated immune responses in riverine buffaloes of various age groups. The
protective efficacy of these vaccines against abortions was also evaluated by
challenge protection studies. Protein antigen of Brucella abortus vaccinal strains
involved in protection was identified by western blot analysis. Moreover an indirect
enzyme linked immunosorbent assay (I-ELISA) for detection of anti-brucella
antibodies in buffaloes was developed. The diagnostic sensitivity and specificity of
developed test was compared with commercial ELISA test. Agreement between the
two tests for negative sera was 100% and for positive sera it was 78%. In the
vaccination study using S19 the peak antibody titres (P<0.05) were observed 30 days
post vaccination using I-ELISA and Rose Bengal plate test (RBPT). The mean
ELISA titre persisted for 3 to 4 months in the vaccinated buffaloes but waned
quickly in calves than adults and heifers. The agglutinating antibodies detected by
RBPT declined below the analytical threshold earlier than ELISA. Vaccinated and
non vaccinated control animals were challenged subcutaneously with 5× 109 cfu of
virulent Brucella abortus during 1st gestation after vaccination. Significantly lower
(P<0.1) abortions were observed in vaccinated animals. In SRB51 vaccinates
significant increase (P<0.05) in the humoral immune responses were detected in all
the three age groups by an I-ELISA using acetone killed SRB51 antigen 30 days post
vaccination. However, all SRB51 vaccinates were detected negative by RBPT. The
vaccinated and control animals, when challenged with locally isolated virulent biovar
1 between 6-7 months of gestation, revealed non-significant (P>0.1) differences
between the probabilities of abortion occurrence. However, the percentage of
abortion occurrence in vaccinated animals (44%) was lower than the non-vaccinated
buffaloes (78%). Lymphocyte proliferation assays detected moderately high and
consistent proliferative responses in all of the S19 vaccinated adults, heifers and
calves after 6 weeks of immunization. The lymphocyte proliferative responses of
SRB51 vaccinate were low and inconsistent and only 77% of the immunized animals
exhibited positive proliferative responses. Western immunoblot analysis using
antisera raised against all three B. abortus strains in buffaloes indicated a near similar
pattern of immune-reactive OMPs in S19 and field strain. Two OMPs of molecular
weight 37-38 and 19 kDa were immuno-reactive in all strains in buffaloes. Two
distinct proteins of molecular weights of 190.5 and 151.3 kDa were identified in field
strain but not in both of the vaccinal strains of B. abortus.