Section II. COMMUNICABLE DISEASES
Not all of the diseases discussed in this subcourse are communicable; however, the
major emphasis is on communicable diseases.
a. Communicable Diseases Defined. Communicable diseases are those
illnesses that can be transmitted from human too human or from animal too human.
Each of these illnesses is caused by a specific infectious agent or its toxic products.
b. Etiologic Agents or Pathogens. Some of the relatively simple forms of life,
classified as viruses, rickettsiae, protozoa, bacteria, fungi, or helminths (worms), are
etiologic (causative) agents or pathogens. All of the disease agents considered in this
publication, with the exception of certain worms and the scabies mite are of microscopic
or submicroscopic size.
SPECTRUM OF INFECTION
a. Definition. Infection is the entry and multiplication of any infectious agent in
the body. The period between infection and onset of signs and symptoms of disease is
called the incubation period.
b. Carriers. However, infection does not always result in recognizable disease.
Frequently the body has enough resistance or immunity to prevent disease
development, in which event a carrier state results.
A carrier can transmit disease in the same way as can a case (a person
who is ill) with the same infection.
Since the carrier is infected but is not sick, the carrier often goes
undiscovered as a source of disease or else is discovered only through very thorough
clinical or laboratory procedures.
c. The Spectrum of Infection. When an infectious agent strikes a community
or military unit, its presence quite likely will be manifested variously in the affected
individuals by all grades of severity, from the inapparent carrier state through the mild
and typical disease states to the most severe and possibly fatal reactions.
For example, one individual with a meningocortical infection may suffer
no more than a sore throat, while another with the same infection may suffer fever,
delirium, and death.
This broad gradation of manifestations of the infectious process in a
group is called the spectrum of infection.