18th June 2024

Background

Tuberculosis (TB) is caused by the Mycobacterium tuberculosis complex, a group of “mycobacteria”; slow-growing obligate aerobic bacteria, so-called for the unique properties of their cell wall. TB ranks as a leading infectious cause of morbidity and mortality worldwide, with approximately one third of the world’s population estimated to be infected and 10 million cases of active disease being estimated in 2020, causing over 1.4 million deaths.

TB is spread mainly via inhalation of aerosolised particles of those with pulmonary tuberculosis, though it may affect any organ system. Inhaled bacilli undergo phagocytosis by tissue macrophages, forming a microscopic structure called a granuloma, mediated chiefly by IFN-γ. Latent TB reactivates (causing “secondary” or “reactivation” TB) in 5-10% of patients on average, with risk factors for reactivation including malnutrition, alcohol excess, diabetes mellitus, immunomodulatory drugs (most notably IFN-γ-targeting monoclonal antibodies) and immunocompromised states (i.e.  HIV infection).