How TB Spreads and Becomes Active

Tuberculosis, or TB, is a bacterial infectious disease caused by Mycobacterium tuberculosis. It usually affects the lungs, which is called pulmonary tuberculosis, but it can also spread to other organs. That wider spread is called extrapulmonary tuberculosis.

TB starts when a person inhales dropl...

The pathophysiology of tuberculosis begins when a susceptible host inhales aerosolized droplets containing Mycobacterium tuberculosis.

The droplets reach the lungs' alveoli, where the bacteria multiply and encounter alveolar macrophages, which engulf them.

However, instead of destroying the bacteria, the macrophages allow them to s...