The present invention relates to an immunogenic polypeptide isolated from Mycobacterium avium subspecies paratuberculosis and variants of the polypeptide. The polypeptide and variants may be used in vaccines against Johne's disease and in methods for detection of the disease. Antibodies against the polypeptide or variants may be used in diagnostic tests for Johne's disease. Also included are polynucleotides encoding the polypeptide and variants, and methods for preparing these.
