Tuberculosis is an acute or chronic lung infections characterized by pulmonary infiltrates and the formation of granulomas with caseation, fibrosis, and cavitation.
Multiplication of the bacillus Mycobacterium tuberculosis causes an inflammatory process where deposited. A cell-mediated immune response follows, usually containing the infection within 4 to 6 weeks. The T-cell response results in the formation of granulomas around the bacilli, making them dormant. This confers immunity to subsequent infection. Bacilli within granulomas may remain viable for many years, resulting in a positive purified protein derivative or other skin test for TB. Active disease develops in 5% to 15% of those infected. Transmission occurs when an infected person coughs or sneezes.