The vast majority of human tuberculosis (TB) cases are due to infection with Mycobacterium tuberculosis, which is generally transmitted through inhalation of the bacilli into the lungs. A more infrequent form of human TB is caused by Mycobacterium bovis, which also causes bovine tuberculosis. Humans can be infected with M. bovis by consuming unpasteurised milk and milk products derived from milk produced by infected animals, or to a lesser extent, by direct contact with infected animals and person-to-person contact. Occasionally, people whose occupation brings them into frequent contact with infected animals or their carcasses, such as farmers and veterinarians, may inhale M. bovis which can result in pulmonary tuberculosis. However, since the transmission of M. bovis is usually foodborne, the most prevalent manifestations are extrapulmonary, e.g. cervical adenitis, genitourinary infections, tuberculosis of the bones and joints and meningitis (Acha & Szyfres, 2003c). Although rare, M. avium and M. caprae have also been reported as causes of zoonotic tuberculosis.
M. bovis is no longer considered a significant zoonotic disease in Ireland, mainly due to the public health measures and animal disease controls in place (TB eradication programme carried out by DAFF). The result is that human infection by M. bovis in Ireland accounts for less than 2.5% of culture confirmed TB cases.