Page 195 - fourth year book

COMMUNICABLE DISEASES (T.B)

Pulmonary TB chain of infection
Causative agent

 TB disease is caused by a bacterium known as Mycobacterium
tuberculosis which are also called tubercle bacilli.

 It is an acid-fast bacterium, aerobic, nonmotile and rod-shaped
bacillus which doesn't form spores.

Reservoir of infection

 Humans are the only known reservoir for M. tuberculosis infection.

Portal of Exit

 TB portal of exit is via the mouth and nose. Infectious droplet nuclei
are generated when persons who have pulmonary or laryngeal TB

disease cough, sneeze, shout, or sing. Depending on the environment,
these tiny particles can remain suspended in the air for several hours.

Mode of Transmission

 M. tuberculosis is transmitted through the air, not by surface contact.
Transmission occurs when person inhales droplet nuclei containing
M. tuberculosis of 1-5 microns in diameter.

Portal of Entry

 TB portal of entry is also its portal of exit--the human respiratory
system. When a person breathes in droplet nuclei, TB bacteria traverse
the mouth or nasal passages, upper respiratory tract, and bronchi to

reach the alveoli of the lungs where it is settled to grow (pulmonary
TB). From there, they can move through the blood to other parts of
the body, such as the kidney, spine, and brain (extrapulmonary TB).

Susceptible Host

 It mostly affects adults in their most productive years however all age
groups are at risk. A person with HIV or AIDS has higher risk to TB
infection.

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