CHARACTERIZATION OF IMMUNE-RESPONSE AND DURATION OF PROTECTION IN BUFFALOS IMMUNIZED WITH HEMORRHAGIC SEPTICEMIA VACCINES

Two of the three buffaloes immunized with a non-adjuvanted broth bacte rin were found to be protected against experimental challenge at 6 wee ks but not at 3 months post-challenge. Similarly all buffaloes (4/4) i mmunized with alum-precipitated vaccine were protected at 6 months but only 1 of the 2 vaccinated animals were protected at 12 months post-i mmunization. On the other hand, buffaloes immunized with an oil adjuva nt and a double emulsion vaccine were completely protected at 12 month s post-immunization. Statistically significant differences between imm unized versus nonimmune animals became evident at 3 months post-immuni zation, although analysis of cumulative antibody titres of pre-challen ge sera of vaccinated buffaloes surviving versus those succumbing to e xperimental challenge revealed significant by higher antibody titres i n the former as compared to the latter group. These results suggested that there was a relationship between ELISA antibody titres and active protection in buffaloes. There also appeared to be a relationship bet ween cutaneous delayed-type hypersensitivity and active protection in buffaloes. Preliminary analysis of the antibody isotype distribution i n the pre-challenge sera of 2 buffaloes vaccinated with the oil adjuva nt vaccine revealed predominance of IgG1 and IgG2 subclasses whose rol e in protection against haemorrhagic septicaemia was not eludicated.