Pigs are susceptible to Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium avium complex. M avium avium and M avium hominissuis are the most frequently isolated. Granulomatous lesions are usually found in the cervical, submandibular, and mesenteric lymph nodes; in advanced disease, however, lesions may also be found in the liver and spleen. Typically, enlarged nodes contain small, white or yellow, caseous foci, usually without any evidence of mineralization. Pigs with disease due to M tuberculosis may have similar regionalized lesions.
Free-range pigs are particularly susceptible to M bovis, which is usually acquired via shared grazing or contact with infected wildlife or production animals. Infection can cause a rapidly progressive, disseminated disease with caseation and liquefaction of lesions. Serologic assays are particularly suitable for TB diagnosis in pigs.
