Serological and cutaneous testing of bovine tuberculosis with the A60 antigen complex from Mycobacterium bovis, strain Calmette-Guérin

A60, a major thermostable macromolecular antigen complex of Mycobacterium bovis strain Calmette-Guerin (BCG), is immunodominant in tuberculosis and able to elicit both humoral and cellular immune reactions in infected hosts. A60-based ELISA and cutaneous tests have been used, in conjunction with the PPD-based skin reaction, in a control group of healthy animals, and in a herd including tuberculous animals. Cutaneous testing with A60 yielded results comparable with those with PPD: both were negative with control cattle and positive with infected animals. Moreover, comparative cutaneous testing with avian tuberculin yielded similar results with PPD and A60. When animals from the infected herd were tested with both avian and bovine sensitins, 54% of cattle were diagnosed as fully positive, 26% suspect, and 20% negative. Serological analysis with the A60-ELISA of part of the infected herd yielded 74% positive, 21% suspect and 5% negative results. Thus, positivity was 74% for serological analysis and 54% for cutaneous testing, whereas positive plus suspect results were 95% for serological analysis and 80% for cutaneous testing. It can be concluded that A60 can be used in place of PPD for cutaneous testing in cattle, and that the diagnostic value of the A60-ELISA is superior to that of the PPD-cutaneous test.