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Pathogenesis of Tuberculosis: Mechanisms of Infection and Transmission

Introduction

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, remains a significant health concern globally. Understanding its pathogenesis is crucial for developing effective preventive and therapeutic strategies.

Transmission

Airborne Droplet Transmission

TB is primarily spread through airborne droplet nuclei, which are expelled when an infected person coughs, sneezes, or talks. These droplets can remain suspended in the air for several hours and can be inhaled by others, leading to infection.

Pathogenesis of Pulmonary TB

Initial Infection

When M. tuberculosis enters the lungs, it is ingested by alveolar macrophages. The bacilli can reside within macrophages or escape into the extracellular space.

Formation of Granulomas

In response to the infection, the immune system forms granulomas, which are collections of macrophages, lymphocytes, and other immune cells. Granulomas contain the infection but can also provide a reservoir for persistent bacteria.

Pathogenesis of Extrapulmonary TB

M. tuberculosis can also spread through the bloodstream (hematogenous spread) to other organs, leading to extrapulmonary TB. This occurs most often during the initial primary infection.

Terminology

It's important to note that the term “tuberculosis” refers specifically to disease caused by M. tuberculosis, while infections caused by other members of the Mycobacterium tuberculosis complex are termed “non-tuberculous mycobacterial (NTM) infections.”