THE CHAIN OF DISEASE TRANSMISSION
Each case or carrier of a communicable disease potentially represents a step in a series
of events, which may lead to the development of a new case.
a. The Steps in the Chain. Each step in this series is dependent on the
successful completion of the preceding step to form a link in the chain of the spread of
disease. The three links in this chain are:
(1) The source, or reservoir, of disease
(2) The means of transmission (the vector or vehicle)
(3) The individual susceptible to the disease (see Figure 1-1)
b. A Host. Any person, animal, or arthropod, which harbors a disease agent at
any link in the chain, is referred to as a host. An intermediate host is one that acts as a
vehicle in transmitting a disease, while a definitive host is a susceptible that provides
the site in which the agent produces the infection.
COMMUNICABLE DISEASE CONTROL
Disease control measures may be viewed as means of breaking the links in the chain of
disease transmission (see Figure 1-2). If any one of the links in the chain is broken,
disease will not occur.
a. The Weak Link in the Chain. The infection chain for each specific disease
usually has one link that is more vulnerable or easily broken than the others. While the
chain may be attacked at several points on all three links, the major effort usually is
made against the weakest link.
b. Personal Hygiene. The one disease control measure that is applicable to all
three links is personal hygiene.
Personal hygiene is defined as the application, by the individual, of the
principles of healthful living.
It embraces more than mere personal cleanliness.
Achieving a high level of personal hygiene requires the individual to
practice health rules to safeguard his health and health of others.