ELISA serodiagnosis of Johne's disease in cattle.

An ELISA test for the serodiagnosis of M. paratuberculosis in cattle has been developed. The test is based on antigen 60 from BCG. It is specific for myocobacteria and detects M. bovis and M. paratuberculosis antibodies. The correlation between sero-units and complement fixation is not an absolute one. On the basis of these preliminary results, a cut-off established at an optical density (OD) of 0.42-0.45 when the sera are analysed at a 1:100 dilution, corresponding to 200 serounits, seems to be adequate. The greatest usefulness of the test appears to consist in the exclusion of a presumed mycobacterial infection.