M. tuberculosis appears unable to sustain (i.e. through cycles of infection, disease and transmission) in non-human animal populations, a fact that has been confirmed using an experimental bovine infection model [1, 9]: while cattle infected with M. bovis display characteristic pathology, cattle infected with M. tuberculosis show minimal pathology despite positive skin-test and IFN-γ responses indicative of successful infection. This evidence concerns the gene IFNG and infection.