PPD prepared from Mycobacterium avium is included as a control antigen representative of the background responses to environmental mycobacterial antigens in the single intradermal comparative cervical tuberculin test (SICCT) as well as the interferon gamma assays used in different countries in bovine tuberculosis (BTB) control strategies (Vordermeier et al., 2006). This evidence concerns the gene IFNG and Tuberculosis, Bovine.