Tuberculosis is a contagious disease caused by Koch's bacillus (Mycobacterium tuberculosis). This infectious agent is transmitted by air, via droplets contaminated with the bacteria suspended in the air from patients. Inhaling a small number of contaminated droplets is enough to infect an individual.

How is tuberculosis transmitted?

The infection is made by inhalation of virulent bacilli which will lodge in the pulmonary alveolus where they are phagocytosed by the alveolar macrophages. This is the stage of primary infection.

The lesions caused by the primary infection heal but constitute possible foci of subsequent reaction. The majority of primary infections are in childhood, they remain silent or cause only minimal symptoms.