Page 198 - fourth year book

COMMUNICABLE DISEASES (T.B)

d. Health system issues: delayed diagnosis and treatment increase
the duration in which active cases are infectious, thereby
sustaining TB transmission

Risk factors for Tuberculosis infection and disease

Pathogenesis and progress of TB disease
 When infection occurs after inhaling droplet nuclei containing
tubercle bacilli that reach the alveoli of the lungs.

 Through innate immune mechanisms these tubercle bacilli are
ingested by alveolar macrophages and destroyed or inhibited. A small
number of them may multiply intracellularly and are released when
the macrophages die. If alive, these bacilli may spread by way of
lymphatic channels or through the bloodstream to more distant
tissues and organs (lymph nodes, apex of the lung, kidneys, spine,
brain and bone). This process of dissemination primes the immune

system for a systemic response.

 Within 2 to 8 weeks, special immune cells called macrophages ingest
and surround the tubercle bacilli. The cells form a barrier shell
(granuloma) that keeps the bacilli contained and under control (LTBI)
in 95% of cases. The progress of early primary TB disease can be

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