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  Indian J Med Microbiol
 

Figure 1: Evolution of nontuberculous mycobacteriosis incidence. (a) For most of the 20th century, the interaction between environmental bacteria and the human host rarely resulted in a mycobacteriosis, as a consequence of mycobacteria localized in environmental niches and the general resistance of the human host. (b) From the last quarter of the century to present, human manipulation of the environment favored the multiplication and dissemination of mycobacteria, increasing the infection dose of individuals more frequently immunocompromised. The interaction between environments that favor nontuberculous mycobacteria, including behavioral changes such as the widespread use of showers, and immunocompromised hosts, induced by factors such as the current use of immunosuppressive therapies, has resulted in a remarkable rise in mycobacteriosis incidence. (c) Frequent exposure of mycobacteria to immunocompromised hosts may facilitate the development of mycobacteriosis. (1) Immunocompromised hosts offer a new favorable environment that allows mycobacterial mutators to adapt and increase its virulence (darker bacilli). In contrast, immunocompetent hosts exposed to expelled mycobacteria are able to resist the infection and the transmission chain is curtailed. (2) After several cycles of exposure to immunocompromised hosts, the mycobacteria pathogenicity may increase to such degree that they become true pathogens. In this circumstance, resistant individuals to environmental mycobacteria may be unable to prevent the survival and multiplication of the new pathogen, which becomes transmissible. Under this situation, nontuberculous mycobacteriosis incidence may overcome that of Mycobacterium tuberculosis

Figure 1: Evolution of nontuberculous mycobacteriosis incidence. (a) For most of the 20<sup>th</sup> century, the interaction between environmental bacteria and the human host rarely resulted in a mycobacteriosis, as a consequence of mycobacteria localized in environmental niches and the general resistance of the human host. (b) From the last quarter of the century to present, human manipulation of the environment favored the multiplication and dissemination of mycobacteria, increasing the infection dose of individuals more frequently immunocompromised. The interaction between environments that favor nontuberculous mycobacteria, including behavioral changes such as the widespread use of showers, and immunocompromised hosts, induced by factors such as the current use of immunosuppressive therapies, has resulted in a remarkable rise in mycobacteriosis incidence. (c) Frequent exposure of mycobacteria to immunocompromised hosts may facilitate the development of mycobacteriosis. (1) Immunocompromised hosts offer a new favorable environment that allows mycobacterial mutators to adapt and increase its virulence (darker bacilli). In contrast, immunocompetent hosts exposed to expelled mycobacteria are able to resist the infection and the transmission chain is curtailed. (2) After several cycles of exposure to immunocompromised hosts, the mycobacteria pathogenicity may increase to such degree that they become true pathogens. In this circumstance, resistant individuals to environmental mycobacteria may be unable to prevent the survival and multiplication of the new pathogen, which becomes transmissible. Under this situation, nontuberculous mycobacteriosis incidence may overcome that of <i>Mycobacterium tuberculosis</i>