e. Fungi. Fungi are nongreen plants that do not produce their own food. They
are parasites; that is, they take their nourishment from other plants or animals on which
or in which they live. Disease-producing fungi include molds and yeasts. Diseases
include dermatophytosis (ringworm such as "athlete's foot") and several forms of
f. Parasitic Worms. Parasitic worms are multicellar animal organisms that live
within the body. They destroy body tissue and can cause disorders such as dysentery.
A major danger is parasitic worms in the blood. These worms can "clog up" a blood
vessel. The tissue supplied by the blood vessel may not be able to obtain a sufficient
supply of oxygen and nutriments. If this is the case, the tissue will die.
The reservoir is the person or animal in or on which the causative agent lives.
The reservoir can be any member of the animal kingdom (human, dog, pig, snail, bird,
flea, and so forth.). When a person is the reservoir, he is usually classified either as
being "ill" or being a "carrier."
a. Ill. A person who is ill is having signs and symptoms caused by the disease.
For example, a person who is sneezing, blowing his nose, running a temperature, and
not feeling well may be showing signs and symptoms of the common cold.
b. Carrier. A person who has a disease, but shows no signs or symptoms of
the disease is called a carrier. This person can spread the disease just like the person
who is ill. The carrier is actually the more dangerous of the two. Since he shows no
signs of being ill, he does not seek medical treatment for the disease nor does he take
any special precautions to keep from spreading the disease to others. A famous carrier
was "Typhoid Mary." She was a food handler who was a carrier of the disease typhoid.
Many people were infected by her until health authorities finally discovered that she was
a carrier of the disease.
MODE OF ESCAPE
As long as the disease-producing organism (causative agent) remains within the
reservoir (diseased person or animal), it cannot infect another human or animal. The
manner in which the organism leaves the reservoir is called the mode of escape.
Disease-causing organisms can escape through various routes including the respiratory
tract (sneezing, coughing, breathing, talking, and so forth.), gastrointestinal tract (fecal
discharges from the bowels), and breaks in the skin (wound drainage, skin lesions, and
so forth.). The destruction of the reservoir can also trigger the escape. For example,
when meat containing parasitic worms is not properly cooked, the worms may escape
from the reservoir (animal flesh) while the meat is being digested.