(4) Systemic ("deep") mycoses infect the internal organs and may spread
throughout the host
c. Those fungi infecting the outer layers of the skin are rarely severe and are
usually transmitted by contact with infected animals or humans. The agents of
subcutaneous and systemic mycoses, however, are normally saprophytic fungi growing
in the soil. Humans generally acquire these mycoses only when the spores of these
organisms are either inhaled or introduced into the body through a break in the skin.
d. Some fungi incapable of causing infectious diseases produce toxic
substances that poison the person who ingests them. These substances are
collectively called mycotoxins. The most commonly known mycotoxin poisoning is from
certain mushrooms; however, mycotoxins may be produced by fungi growing on grain,
nuts, and other agricultural products.
Section V. PROTOZOA
Protozoa are minute, unicellular organisms belonging to the Animal Kingdom
Protista. They range in size from nearly submicroscopic 100u; however, the vast
majority of them are microscopic. Thousands of species have been identified, but
relatively few are pathogenic to man.
a. Morphology. Protozoa vary widely in structure. Some have organelles of
locomotion--flagella, cilia, or pseudopods. Some have definite openings to absorb food.
All consist of one or more nuclei and cytoplasm. Many have various inclusion bodies.
(1) Nutrition. Most protozoa absorb fluid directly through the cell
membrane. Many can take in solid food and digest it by enzymes produced by their own
(2) Reproduction. Protozoa multiply species, and by sexual reproduction in
others. of sexual and asexual reproduction.
(3) Locomotion. Nearly all protozoa possess some means of locomotion.
Some have flagella (figure 2-6); others have cilia (delicate, hair-like organelles); and some
have pseudopods (false feet), which are protoplasmic processes that flow forward in a
manner similar to the action of a balloon partially filled with liquid, pulling the cell along
(4) Cyst formation. Many protozoa have the ability to form cysts
when subjected to an unfavorable environment. This process is similar to spore
formation in bacteria. Since protozoan cysts are much more resistant to unfavorable