Comparison of an indirect ELISA with the Brucella milk ring test for detection of antibodies to Brucella abortus in bulk milk samples.

An indirect enzyme-linked immunosorbent assay (ELISA) for the detection of Brucella abortus antibodies in bovine bulk milk samples was evaluated. About 31 individual milk samples from B. abortus infected cows were diluted into bulk milk from a brucellosis free herd. Individual milk samples obtained from 96 negative or positive herds to ELISA or Brucella ring test (BRT), were tested by ELISA. All positive cows were bled and serum samples were tested by the complement-fixation test (CFT) which was considered the definitive test. A herd was considered infected if at least, one cow was positive in the CFT. Four samples were negative in the BRT at the dilution 1:10 but positive in the ELISA. For samples positive in both tests, BRT titers ranged from 1:10 to 1:480 while ELISA titers ranged from 1:10 to 1:3200. Using bulk milk samples, the sensitivity of the ELISA (98.1%) was higher than the BRT (72.2%) but the specificity of BRT (90.5%) was not statistically different (P=1.0) from the ELISA (88.1%). The implications of the results for brucellosis control are discussed.