Читать книгу Tuberculosis and War - Группа авторов - Страница 49

Host-dependent factors are important conditions that weaken the immune defense system of the body. The defense mechanisms against M. tuberculosis are complex, a variety of factors are involved, from innate and adaptive cellular to humoral immune responses. If these are impaired, it increases TB morbidity, chiefly through increased progression from already present latent infection to active disease with accompanying mortality. Impaired immune defenses are an increasing cause of TB disease and death in developed as well as in underdeveloped countries.

While the risk of becoming infected with M. tuberculosis is largely exogenous in nature as described above, the risk subsequent to acquisition of latent infection with M. tuberculosis is largely endogenous [17]. Thus, crowded congregate settings are conducive to increase the probability of successful transmission of tubercle bacilli. While infection with M. tuberculosis is the necessary or initiating cause, some reduction in the body’s resistance, probably decreased cellular immunity, is undoubtedly the sufficient or promoting cause [18]. What we refer to here as host-dependent factors broadly circumscribes a multitude of factors that increase the risk of progression from latent infection with M. tuberculosis to overt clinical disease by putatively undermining cellular immune defenses [19]. Many of these factors are well established, leaving little doubt about their causal role in increasing the risk of progression to TB (such as diabetes mellitus, silicosis, immunosuppressive therapy with certain drug classes, etc.), while the relationship is causally less certain in others (such as gastrectomy, certain blood groups). One factor of major global implication because of its shear population magnitude is malnutrition or, more precisely, protein energy malnutrition.

Fig. 4. Tuberculosis mortality comparatively shown for Denmark and The Netherlands, 1913–1922, with the time indicated for an abrupt change in nutrition for the Danish population as a result of policy change imposed by the warring countries, data from [28].