Hazards of Bovine Tuberculosis as a Matter of Public Health Significance and Potential Human Lung Infections with Bovine Tubercle Bacilli

SUMMARY Following discovery of the tubercle bacilli by Professor Koch, three types of the organism were soon recognized immunologically as separate and distinct entities, i.e., the human, bovine and avian. For several years thereafter, Koch, as well as many other reputable scientists in the field of bacteriology, contended that host-species in each category would not contract tuberculosis when exposed to other types of the bacilli and, therefore, bovine tuberculosis was not transmissible to man. However, that conclusion was later exploded and Koch, after much reluctance, finally changed his former opinion in the premise. Consequently, the transmission of tuberculosis from animal to man soon became a generally accepted fact but not without reservations as to its clinical effects. A consensus of opinion prevailed that, although transmissible to man, the condition produced by the bovine tubercle bacilli was confined mainly to certain circumscribed limitations such as glandular or lymph node infections and tuberculosis of the bone and joints, but it was not considered to be more than passively capable of producing pulmonary lesions of tuberculosis. With the development of better methods and more practical means of typing, greater stress in recent years has been attached to the importance and desirability of identifying the type of bacilli actually responsible for the disease when it occurs in man. Today the bovine bacilli stand convicted not only as the causative agent of a variety of clinical forms, including progressive tuberculosis in man, but pulmonary tuberculosis of bovine origin has been established either clinically or on autopsy in an increasing number of human cases, particularly in European countries where tuberculosis flourishes to a much greater extent among cattle at the present time. Also an increasing number of generalized cases of tuberculosis in humans attributed to the bovine bacilli have been reported in several of these countries. Thus far in the conquest of bovine tuberculosis, approximately 279.500.000 tuberculin tests have been applied in more than 22, 000,000 lots of cattle scattered through the United States, resulting in the condemnation and slaughter of approximately 3,892,000 animals that revealed positive reactions to these tests. Following this systematic process of tuberculin testing of cattle at regular intervals since the inauguration of the eradication project in 1917, the incidence of the disease has been reduced to 0.5 per cent in all of the 3,069 counties in the United States and all municipalities in Puerto Rico and the Virgin Islands, and these states and municipalities have enjoyed the distinctive classification of officially modified accredited areas since November 1, 1940. During the fiscal year 1945 about fourteen and one-half million cattle, exclusive of known reactors, were slaughtered under Federal meat inspection. Only 0.04 per cent were found to be tuberculous and only one in 10,000 was sufficiently infected to warrant condemnation. Therefore, it appears obvious that we have arrived at a point in this country when the dissemination of bovine tuberculosis is no longer a matter of serious concern. Sporadic cases of the disease will occur in mammalians from time to time, be they animal or man, until the disease is finally extirpated. It may also be postulated that a definite challenge may now be encountered toward any further appreciable reduction in the incidence of tuberculosis in cattle so long as tuberculosis exists in any form to plague human or animal life. It is probable, when more data is available in countries where bovine tuberculosis is prevalent to a considerably greater extent among cattle today, in view of a greater tendency toward typing, plus the effects of a prolonged war, that human tuberculosis in all clinical varieties, including pulmonary tuberculosis caused by the bovine tubercle bacilli, will reveal a very conspicuous increase. This potential reflects not alone the extremely favorable situation for those fortunate enough to live in the United States but also the eminence attained by this country in the field of tuberculosis eradication among cattle, an achievement not emulated by any other country, and one to which we point with scintillating pride as reminiscent of the fact that bovine tuberculosis is a constant menace to human health, life and general welfare and, although economically destructive and insidious, yet, a disease possible of eradication.