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(460) Tuberculosis is a disease affecting human beings, mammals and birds. The causal organism Mycobacterium tuberculosis is sub-classified into types based on the species of host usually affected: the human type generally referred to as M. tuberculosis affects people and primates, the bovine type M. bovis, affects cattle, badgers and other wild herbivores and sometimes people; and the avian type, the M. avian/M. intracellulare complex, affects mainly birds. Pigs are susceptible to all three but in practice are rarely infected by the first two. Most TB in pigs is caused by the avian/intracellulare complex which 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. The disease does not therefore spread between pigs and is rarely diagnosed in living pigs. Similarly, the M. avium/intra-cellulare complex causes non-progressive infection in normal healthy people. The main concern is that the M. avium/intracellulare could cause more serious disease in immuno-suppressed people and people with AIDS and the lesions in the pigs carcase at slaughter cannot be distinguished from human and bovine TB which would cause progressive disease in otherwise normal people. Therefore, in most countries if lesions are found in the neck at slaughter the whole head is condemned and if they are found in the mesenteric lymph nodes which drain the intestines the offals are condemned. If they are more widespread the whole carcase may be condemned or require cooking. If small lesions are missed by the meat inspector cooking will normally destroy the organism.

The sources of infection to the pig include:

  • Outdoor pigs - grazing land that as has been treated with poultry manure even up to one year previously, or that which has been grazed by infected cattle or badgers infected with M. bovis.
  • Avian TB as the name implies is found in wild birds and in particular starlings. The organism is shed in large numbers via droppings and therefore food or grain contaminated by birds becomes a potent source.
  • Sawdust/shavings can be a major source of infection.
  • Peat often contains M. intracellulare and is capable of causing lesions at slaughter. Peat is used both for bedding and gut stimulation in the young piglets. It should only be used if it as been pasteurised.
  • Water contaminated by M. avium/intracellulare is often a source.
  • Infection may occur from 10 weeks onwards with lesions seen at slaughter. Lesions can take up to 8 weeks or more to develop.
Clinical signs

M. avian infection has no clinical effect and there is no difference in performance between infected and non-infected pigs.


TB in living pigs can be diagnosed using the skin tuberculin test but usually detected in the cervical and intestinal lymph glands at meat inspection. Normal levels are less than 1%.

Management control and prevention

  • If disease is evident at slaughter, consider the above potential sources and eliminate them. Remember that avian/intracellulare is an environmental contaminant - the environment is the source.

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