Figure 1.

The human tuberculosis (TB) life cycle.

A patient with pulmonary TB generates an aerosol by coughing, which is inhaled into the lower part of the lungs. Initial proliferation occurs, often leading to a Ghon focus visible on the chest X-ray (circle). In the absence of an efficacious immune response, disseminated miliary TB develops, with mycobacterial proliferation in many organs, but this is a dead end for the pathogen. Once the adaptive immune response activates, Mycobacterium tuberculosis (Mtb) proliferation is controlled, and a period of latency typically occurs. Infection can reactivate in other organs, such as lymph nodes, but again this does not typically transmit. In ~6% of individuals, typically those aged 20–25 with a robust immune response, Mtb drives extensive lung inflammation, leading to lung matrix destruction, cavitation, and transmission to new hosts. However, even extensive lesions can regress, with approximately one-third of ‘consumptives’ spontaneously healing during the pre-antibiotic era. Part of figure created with BioRender (www.BioRender.com').