Pigs are susceptible to M.tuberculosis, M.bovis and M.avium but in practice infection by the first two is rare, although not impossible. Infection with M.avium usually occurs through environmental contamination by infected birds (faecal contamination of food and water, for example). M.bovis infection in pigs can result from pigs scavenging dead carcases, e.g. infected badgers, or from consuming feed or water contaminated with the tuberculosis bacteria (which could include contaminated pasture land).
Infection causes small nodules in the lymph nodes of the neck and those that drain the small intestine. In the great majority of cases the lesions are non-progressive, they do not spread through the body, do not make the pigs ill and the organisms are not shed.
Bovine TB is not considered to be particularly contagious amongst pigs or to spread easily from pigs to other animals. It is commonly viewed as self-limiting.
Number of infected (positive for M.bovis on culture) animals by year and species
TB in living pigs can be diagnosed using the skin tuberculin test but there is no active disease surveillance program in the UK so bTB is usually detected in the cervical and intestinal lymph glands at meat inspection, post slaughter. Normal levels are less than 1%. There is no compensation paid for TB reactors in pigs