1-7.
FUNGI
a. Characteristics. Yeasts and molds are classified under the category of
fungi. Fungi range in size from around 3 microns to 20 microns. Fungi are often visible
as colonies with the unaided eye. Typically, fungi cause infections on the skin. These
infections are not usually serious (for example, life-threatening); however, if a fungal
infection becomes systemic, it becomes very difficult for the patient to recover.
b. Fungi and Disease. A very common fungal ailment is "athlete's foot", which
is caused by Trichophyton mentagrophytes or Epidermophyton floccosum. Ringworm
(a fungal infection, not really a worm infestation) can affect both the scalp area and the
general body surface. Ringworm is caused by Microsporum canis or Microsporum
gypseum. Thrush (also called sprue); a fungal disease characterized by white patches
in the mouth and throat is caused by Candida albicans. This condition is common in
people who are on chronic antibiotic therapy. Candida infections can also occur in the
vagina and urinary tract.
1-8.
PROTOZOA
a. Characteristics. The protozoa are the smallest animals and the largest
microorganisms. You have probably observed some protozoa using a microscope in
biology class. These organisms are plentiful in streams and lakes. While most
protozoa are harmless to humans, some of these organisms can cause disease.
b. Protozoa and Disease. Several protozoa are of key military medical
significance.
(1) Trichomonas vaginalis. Trichomonas vaginalis is a small, one-celled
protozoan that has several ship-like flagella for locomotion. This organism causes
inflammation and a purulent (pus-like) discharge from the vaginal tract in women. It can
also cause a urinary tract infection in males. Occasionally, the organism is found in the
mouth (leading to gingivitis, inflammation of the gums) and in the intestine (leading to
diarrhea). This organism can be transmitted by sexual contact, but it can also be
carried on moist clothing or towels. These particular organisms can be killed by drying.
(2) Entamoeba histolytica. Entamoeba histolytica is an organism that
causes amebiasis. Amebiasis is primarily restricted to the large intestine. In this
disease, the patient experiences inflammation of the colon with diarrhea and watery
stools that contain blood, mucus, and pus. This stage of the condition is frequently
called amoebic dysentery. Should the intestine become perforated (that is, develop a
hole), there will be excessive internal bleeding and infection of the soft tissues of the
body (such as the lungs, spleen, liver, and brain). The organism usually enters the host
in a cyst form (that is, thick-walled form resistant to environmental changes). Once
inside the host, it has the ability to emerge from the cyst (infective stage). The spreading
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