TUBERCOLOSIS. – An infectious disease generally following a chronic course, but sometimes tumultuous and fulminant, produced by a particular bacillus (Mycobacterium tuberculosis) identified by R. Koch in 1882.
The disease has an almost ubiquitous distribution and affects all ages, so much so that, excluding infants, it is estimated that 40–50% of cadavers present lesions due to t. as the cause of overt or latent disease. Clinically, the disease is more frequent between the 2nd and 7th years of life, but mortality reaches its peak between the 14th and 30th years.
All ages may, however, be affected, including old age, with lesions involving the most varied organs and systems, although localization in the lungs is by far the most frequent (70% in adults). The enormous diffusion of t. is also attested by some recent anatomopathological statistics by Naegeli (Zurich), according to which lesions due to t. would be found in 15% of cases in the first decade of life, in 30–60% in the second decade, and even in 99% in the final decades of life. According to Hamburger and Monti (Vienna), moreover, the tuberculin skin reaction (an index of a manifest or latent, active or already overcome tuberculous infection) would be positive in 99% of subjects as early as the 14th year of life.
Koch’s bacillus, in the form of a slightly curved rod, is characterized by particular resistance to acids and ordinary antiseptics, by virtue of the waxy covering capsule with which it is provided. This same capsule is probably also responsible for the limited efficacy of the various therapeutic methods known today and for the long survival of the germ in the external environment. Three different types of bacilli of t. have now been identified: human, bovine, and avian; only the first two, however, appear to be of importance in human pathology. These germs, having entered the organism, generally through the respiratory tract (96% of cases), or also by ingestion (1.4% of cases, mostly infants fed on milk from tuberculous cows), produce characteristic alterations in the tissues, with the formation of the so-called «tubercles» or «tuberculous granulomas», which invariably evolve toward a particular type of tissue necrosis, «caseous necrosis». Subsequently, depending on the virulence of the germ and the reactivity of the organism, there may be a relatively benign course, with fibrous transformation and calcification of the tuberculous process (productive forms); or, conversely, liquefaction may occur in the preformed caseous substance, with ulceration and destruction of the host’s tissues and the formation of cavities and ulcers (exudative and caseous forms). Naturally, such a rigorous schematization does not always apply, and in clinical practice the two processes may be simultaneously present or alternate, so that Micheli more appropriately speaks of «predominantly productive forms» and «predominantly exudative forms».
For a long time t. was considered a hereditary and familial disease, but ideas have now changed considerably. Hereditary t.—that is, linked to the «genes» (preformed elements carrying hereditary characteristics, contained in the spermatozoon and ovum) and transmissible according to Mendelian laws—is today excluded by all authors. In very rare cases one may speak of congenital t., since this can be admitted only by demonstrating an ultraviral phase of Koch’s bacillus, thereby capable of crossing the placental filter from mother to fetus, something which, moreover, has not been demonstrated. The only possible cases, therefore, are those caused by passage of the germ through possible placental lesions during pregnancy; hence the general rule now holds: one is not born tuberculous but becomes tuberculous. There is, however, unquestionably a particular hereditary predisposition to falling ill with t., demonstrated by statistics showing that the children are tuberculous in 43% of cases if both parents are ill, in 33.15% if only one is sick, and in 24.6% when the parents are healthy. Thus, rather than true heredity of the disease, one must speak of hereditary predisposition, linked to the particular constitution that the individual possesses at birth and that makes the individual more liable to succumb to tuberculous infection. It has in fact been observed that two particular biotypes (v.) provide the greatest number of patients: the asthenic longilinear biotype (the Hippocratic phthisical habitus, Stiller’s asthenic habitus), and the lymphatic biotype with exudative diathesis (Czerny’s pasty habitus). The former, however, because of the poor reactivity of its tissues, readily succumbs to the germ, presenting the most severe forms with ulcerative and necrotizing progression; the lymphatic biotype, on the other hand, endowed with hyperactive defensive connective tissue, generally presents chronic, circumscribed forms with fibrous progression and therefore a relatively benign course. Alongside a predisposition to t., however, one must recognize the coexistence of a relative immunity to the disease, as demonstrated by the fact that populations previously free from tuberculous infection, once they came into contact with Koch’s bacillus, showed a much higher mortality than populations in which t. is considered an endemic disease. In this regard, the case of the inhabitants of the island of Tahiti is sufficient: having accidentally come into contact with Koch’s bacillus through Portuguese colonization, they suffered, in a short time, an 87.5% mortality from t., and the population fell from 80,000 to 7,000 individuals.
These contrasting facts are today explained by the modern theories of allergy and immunity (v. MICROBIOLOGIA), so much so that in the field of t. one speaks specifically of a «tuberculous allergy», in the sense of a reaction deviated from the normal. Ranke, who devoted much attention to the problem, distinguishes three phases in the allergic process of the organism after contact with the bacillus of t. The first stage is characterized by an intense reaction of the affected tissue and the formation of the «primary complex»; the second by a tendency toward generalization of the process because of tissue hypersensitivity to the harmful action of the germ; and the third, finally, by relative immunity and a tendency of the lesions to localize in a single organ. This simplicity and schematization may be excessive and cannot fully clarify the complex allergic problem of t.; nevertheless, it is quite useful in clarifying the differences in behavior, not only among individuals but among entire populations, in the face of tuberculous infection. Among European populations, in fact, it is much more common for investigations into the existence of a tuberculous infection to yield a positive result from the earliest years of life; on the other hand, continual contact with the germ and its toxins means that benign productive forms, due to the state of relative immunity, prevail clinically.
From the clinical point of view, tuberculosis may be distinguished into primary tuberculosis (characterized by the “primary complex,” for the most part localized in the lung) and post-primary tuberculosis, which, although it favors the lungs, may be localized in any other organ or region (serous membranes, nervous system, peritoneal organs, bones, urogenital apparatus, endocrine glands). The course of the various localizations is generally chronic; but at times tuberculosis assumes a tumultuous and rapidly fatal course, whether on account of the extent of the process (miliary forms), its intrinsic severity (galloping phthisis or confluent caseous bronchopneumonia), the importance of the organ involved (tuberculous meningitis, tuberculosis of the adrenal glands), or the subject’s particular state of vitality (tuberculosis in infants and alcoholics). At other times tuberculosis may run an entirely asymptomatic course and pass unnoticed by the individual; such insidious forms nevertheless have great medical and social importance, constituting a continual source of contagion for the community. Tuberculosis is in fact of the greatest social importance, both because of the harm it causes to eugenics and to the demographic development of a nation (some authors attribute to tuberculous intoxication of the fetus the capacity to produce states of psychodegeneration), and because of the economic harm it may cause through its characteristic chronicity, as well as because of its contagiousness and the high mortality mentioned above.
The campaign against tuberculosis is conducted first of all actively in a prophylactic sense. This prevention is today carried out everywhere directly by the State, or at least under its control, along two lines: strengthening the organism so as to increase its capacity to resist infection, particularly during the developmental period (establishment of colonies for predisposed persons, supplementary rations, vaccinations, various hygienic regulations); and reducing the possibility of contagion to the minimum through the isolation of the sick (sanatoria, villages constructed especially for this purpose, such as those at Papworth in England and Claire-vivre in France) and the disinfection of premises.
In addition to the prophylactic field, considerable progress has been achieved in the therapeutic field during these last decades. Current therapy aims principally at three objectives: increasing the defensive powers of the organism, combating Koch’s bacillus, and circumscribing and reducing by every means, including surgery, the lesions already produced, so as to prevent the spread of the disease and bring about the formation of a permanent scar. Important, therefore, were the discoveries of certain drugs possessing bacteriostatic and bactericidal power against Koch’s bacillus, such as “soifone,” “streptomycin,” “para-aminosalicylic acid,” and “isonicotinic acid hydrazide.” These have made it possible to alter favorably the prognosis of certain tuberculous forms once considered to have a constantly unfavorable outcome, such as miliary tuberculosis and tuberculous meningitis. Equally satisfactory results have not been obtained with these drugs in pulmonary cavitary forms, in which every chemotherapeutic treatment must be combined with collapse therapy. This therapy, initiated by Forlanini, is based essentially on the principle of placing the diseased part of the lung at rest so as to permit the tuberculous lesion to heal readily. The essential method is therefore pneumothorax (pnx), by which air is introduced into the pleural cavity in an amount sufficient to neutralize the negative pressure normally present there. With time, this method has been increasingly perfected and has also undergone modifications, so that today one distinguishes not only between a hypertensive and a hypotensive pnx, an ipsilateral, a contralateral, and a bilateral one, but also performs extrapleural pnx when the presence of excessive adhesions between the parietal and visceral pleura prevents the introduction of air into the pleural cavity. There are also today numerous other methods of collapse therapy belonging properly to the surgical field, but not without beneficial effect in certain circumstances (pleurisy, intrapleural procedures, phrenicectomy, partial or total removal of the diseased lung, etc.). According to the majority of modern authors, tuberculosis therapy in pulmonary forms must always be based on collapse therapy; nevertheless, the beneficial effect of antituberculous drugs cannot be denied, especially from the social standpoint, given their capacity to render tuberculous patients no longer contagious. As is known, such patients transmit the disease in their surroundings through microscopic droplets of saliva projected by coughing and containing Koch’s bacilli.
A final reference must be made to the medico-moral problems connected with tuberculosis. These concern particularly the hospitalization of the sick, the imposition of an examination to establish whether or not the disease is present, marriage, and pregnancy. In all these cases, the inevitable conflict is evident that coercive legislation, which places the interest of the community in the foreground, may have with regard to the rights of the human person. Finally, it should be recalled that until a few years ago tuberculosis constituted one of the most abortion (v.). At present, however, the majority of physiologists and gynecologists hold that, although on the one hand it may be advisable in certain severe forms to avoid pregnancy, on the other hand therapeutic abortion must be proscribed because of the serious harm inevitably entailed by the interruption of pregnancy; all the more so because in the most severe forms spontaneous abortion occurs readily and is less traumatic and dangerous than induced abortion.
maine, in Minerva medica, 41 (1950), p. 23 sgg.; M. Bufano, Tratt. di patol. speciale med. e terapia, 2ª ed., Milano 1949; G. Motta, Aborto terapeutico e the polmonare, in Gazzetta sanitaria, 22 (1951), nn. 8-9; G. de Ninn, Quest. medico-morali, 4ª ed., Roma 1951. Alessandro Marolla