John D. McKinney, Global Health Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), provides an overview of the natural history of TB infection and the global impact of TB on human health.
"Human population growth and urbanization have accelerated dramatically in recent centuries, providing unprecedented opportunities for microbes that use our bodies as vehicles for their own propagation and transmission. These conditions have led to the emergence of virulent new pathogens and the increased prevalence of "classic" scourges, such as Mycobacterium tuberculosis. This tenacious microbe is transmitted via infectious aerosols produced by individuals with pulmonary tuberculosis. Infection is lifelong and symptomatic tuberculosis may develop following a period of clinical latency lasting for months, years, or decades."