COMPARISON OF 4 ELISA TECHNIQUES IN THE E VALUATION OF THE SEROLOGICAL RESPONSE OF HEIFERS VACCINATED WITH BRUCELLA-ABORTUS STRAIN-19

The humoral immune response in heifers vaccinated with Brucella abortu s strain 19 was evaluated using four ELISA techniques. Sixteen 5 month s old heifers were vaccinated subcutaneously with a standard dose of B rucella abortus strain 19. Sera from all heifers were obtained in 18 o ccasions (first 87 days before vaccination one immediately before vacc ination and 16 samplings once monthly during 488 days after vaccinatio n) and analyzed by indirect ELISA with polyclonal conjugate, indirect ELISA with monoclonal conjugate, competitive ELISA using the smooth li popolysaccharide of B. abortus as antigen and competitive ELISA using the O chain of the smooth lipopolysaccharide of B. abortus as antigen. Prior to vaccination, 100% of the heifers gave negative results with all the techniques used, while 100% of them gave positive reactions to all the techniques in the first sampling after vaccination, showing a decreasing percentage of positive animals, and giving no positive ani mals at different times after vaccination (the two indirect ELISA tech niques at day 488, the competitive ELISA using the smooth lipopolysacc haride of B. abortus as antigen at day 363 and the competitive ELISA u sing the O chain of de smooth lipopolysaccharide of B. abortus as anti gen at day 253). These results show that the diagnosis of bovine bruce llosis in animals older than 18 months, with the techniques used in th is study, is not affected by residual antibodies after vaccination wit h Strain 19 at 5 months of age.