The use of Ag85 complex as antigen in ELISA for the diagnosis of bovine tuberculosis in dairy cows in Brazil.

Several enzyme-linked immunosorbent assay (ELISA) methods have been investigated to evaluate their performance in the diagnosis of tuberculosis in cattle. Increased production of antibodies to the proteins of antigen 85 complex (Ag85) after experimental and natural infection in cattle shows that they are strongly immunogenic in vivo. The purpose of this study was to evaluate the use of Ag85 as an antigen in ELISA for the diagnosis of bovine tuberculosis in dairy cows in Brazil. The test groups consisted of 46 serum samples from intradermal tuberculin test (ITT)-positive animals (Group A) and 46 samples from ITT-negative animals (Group B). Group C comprised 12 samples from a tuberculosis-free herd and was the control group of the study. Samples were tested in an ELISA using Ag85 as antigen. Differences between the mean ODs of groups A and B and A and C were significant (P < 0.01), but no significant difference (P > 0.05) was observed between groups B and C. The sensitivity of the ELISA using Ag85 was 91.3% (42/46) and its specificity was 94.8% (55/58). These results were not significantly different (P > 0.05) from those observed in a previous study of an ELISA using purified protein derivative (PPD). We concluded that, although Ag85 can be used as antigen for ELISA tests in the diagnosis of bovine tuberculosis with good sensitivity and specificity rates, no significant advantages were observed in relation to the ELISA using PPD that could justify the purification and utilization of Ag85 as a single antigen in routine methods of diagnosis.