k. Incubation Period. The incubation period is the time interval between the
entrance of an infectious agent into a host and the appearance of symptoms.
l. Spectrum of Infection. The spectrum of infection is the broad gradation of
disease infection from no apparent symptoms (such as the carrier state) through severe
illness and death.
m. Endemic. Endemic refers to the usual level of occurrence of a disease within
a given geographical area.
n. Epidemic. Epidemic is the occurrence of a disease clearly in excess of the
normal expectancy within a given geographical area.
o. Pandemic. Pandemic is the occurrence of disease over a wide geographical
area and affecting an exceptionally high percentage of the population.
p. Epidemiology. Epidemiology is the study of the determinants and
distribution of disease and injury in a given population.
q. Vehicle. A vehicle is an inanimate object that facilitates the transmission of a
Although not all diseases of military importance are communicable, this lesson
will focus upon the communicable diseases-those that can be transmitted from person
to person or from an animal to a person. These diseases may be classified into five
groups, based upon the manner in which they are spread, the area of the body that they
affect, and the type of control needed to prevent their spread.
a. Intestinal Diseases. These diseases are usually transmitted by food or
water that has become contaminated with feces from an infected human or animal.
Examples are typhoid and paratyphoid fevers, dysentery, and cholera.
b. Respiratory Diseases. These diseases are usually transmitted from person
to person by discharges from the nose, mouth, throat, or lungs of an infected person.
Examples are the common cold, influenza, pneumonia, streptococcal sore throat, and
c. Sexually Transmitted Diseases. These diseases are transmitted from
person to person by sexual intercourse. Examples are syphilis, gonorrhea, herpes,
hepatitis B, and chancroid.
d. Arthropod-Borne Diseases. These diseases are transmitted from person to
person or from animal to person by insects or other arthropods. Examples are malaria,
typhus, and yellow fever.
e. Miscellaneous Diseases. This group includes those communicable
diseases that do not fall into any of the above groups. Examples are rabies
(hydrophobia), tetanus (lockjaw), and dermatophytosis (athlete's foot).