HERD HEALTH
PIH-99
pork industry handbook
PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA
Mycobacteriosis (Tuberculosis) in Swine
Authors
Janet B. Payeur, USDA/NVSL, Ames, Iowa
J. Glenn Songer, University of Arizona
Reviewers
John R. Cole, Jr., University of Georgia
Ralph F. Hall, University of Tennessee
John and Teri Peters, Twin Falls, Idaho
Charles O. Thoen, Iowa State University
Introduction and History
Mycobacteriosis, also called tuberculosis, is found in about
0.4% of all hogs slaughtered under Federal inspection (based on United States Department of Agriculture [USDA], Food Safety and Inspection Service [FSIS], records for 1990) and probably costs the swine industry between $5.1 and $6.3 million annually. This is not a large amount compared to losses from other swine diseases. Although there are relatively few infected herds, the economic losses can be devastating to those producers that have the disease in their herds.

Mycobacteriosis in pigs bears almost no resemblance to the disease in cattle or humans. The disease in pigs has no apparent affect on the health of the animal. Apparently it cannot be transmitted to man, either by direct contact or by eating pork products. Lack of transmission of the disease from pigs to man cannot be proven, however. Thus, meat inspection regulations formulated in 1972 call for special handling of carcasses in which evidence of mycobacteriosis is found. Economic losses occur to the swine industry because of these regulations.

Tuberculosis has been largely eliminated in cattle and poultry. Tuberculin testing of cattle with subsequent slaughter of reactors, and in some cases depopulation of entire herds, has lowered the prevalence of the disease to about 0.001% (FSIS, 1990 records) in slaughter cattle. Similarly, the poultry industry has changed to all-pullet flocks and has essentially eliminated tuberculosis. Elimination of older birds has been an effective control measure in this industry. The rate of condemnation for tuberculosis is 0.0001% in light fowl (FSIS, 1990 records).

It has been assumed by many that eradication of tuberculosis from cattle and chickens would automatically lead to its eradication in swine. This has not been the case, however, and mycobacterial infections in swine remain a problem for pork producers today.
Etiology
Historically, the primary agents of mycobacterial disease in swine are the same as those causing tuberculosis in other animals. The disease is transmitted through animal to animal contact. Early in the 20th century when tuberculosis in cattle and man was more prevalent, mycobacteriosis in swine was either Mycobacterium bovis or M. tuberculosis. By 1925, however, M. avium, the cause of tuberculosis in birds, began to occur more frequently in swine. The most common serotypes of M. avium in pigs are 1, 2, 3, 4, 6, and 8. Outbreaks of disease due to these serotypes appear to have originated in soil, contaminated litter, usually sawdust, wood shavings or straw and contact from infected fowl. Today isolation of mycobacteria other than M. avium from swine, is uncommon (less than 4%; National Veterinary Services Laboratories [NVSL]; 1990). From 1985 to 1990, the NVSL isolated M. bovis from swine only 4 times. In each case these pigs were on the same premises with M. bovis-infected cattle.

The public health significance of Mycobacterium avium complex infections in man is now recognized. The most common serotypes of M. avium complex reported from patients with acquired immune deficiency syndrome (AIDS) are serotypes 1, 4 and 8. They are among the most virulent of the known serotypes and are most likely environmental in origin. Since M. avium and other mycobacteria abound in the environment and therefore occur in food and drinking water, it is not surprising that they are present in the human alimentary tract. Thus the alimentary tract could be the source of frequently disseminated M. avium infections in patients with AIDS.

Rhodococcus equi infection in swine also produces a localized lesion that resembles mycobacteriosis microscopically. The earliest reports of R. equi infection in pigs were made during the
Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University, and U.S. Department of Agriculture cooperating; H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an affirmative action/equal opportunity institution.