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 investi gated to evaluate their performance in the diagnosis of tuberculosis in cat tle. Increased production of antibodies to the proteins of antigen 85 compl ex (Ag85) after experimental and natural infection in cattle shows that the y are strongly immunogenic in vivo. The purpose of this study was to evalua te the use of Ag85 as an antigen in ELISA for the diagnosis of bovine tuber culosis in dairy cows in Brazil. The test groups consisted of 46 serum samp les from intradermal tuberculin test (ITT)-positive animals (Group A) and 4 6 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. Samp les 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 > 0.0 5) from those observed in a previous study of an ELISA using purified prote in derivative (PPD). We concluded that, although Ag85 can be used as antige n for ELISA tests in the diagnosis of bovine tuberculosis with good sensiti vity and specificity rates, no significant advantages were observed in rela tion to the ELISA using PPD that could justify the purification and utiliza tion of Ag85 as a single antigen in routine methods of diagnosis.