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Protozoal Microorganisms as Intestinal Parasites 43

symptoms of abdominal pain, diarrhea, weight loss, and
MICROSCOPIC DIAGNOSTIC fever that require treatment other than metronidazole. It

FEATURE was found that by treating the organism as a pathogen,
symptoms concurrently subsided. Only a few symptoms
may occur in some who are infected and only a small
General percentage of these show any overt symptoms or signs.
Classification Amoeba

Organism Dientamoeba fragilis TRICHOMONAS VAGINALIS
Specimen Required Stool specimen
T. vaginalis is a protozoan with flagella that is capable of
Stage Trophozoite only
surviving in an anaerobic (without oxygen) environment.
Size 5–12 μm
It is the most common pathogenic protozoan infection
Shape Irregular and of humans in industrialized countries and infection rates
amoeboid
between men and women are the same. Women often
Motility Nondirectional; con- show symptoms, whereas men do not. The World Health
tains what is thought
to be vestiges of Organization (WHO) estimates that there is a worldwide
flagella and related infection rate of 180 million new cases annually.
to the Trichomonas The organism T. vaginalis is one of the most fre-
organism quently sexually transmitted organisms with many mil-
Nucleus(i) 2 (Approximately lions of cases reported each year. In most states and in
50–80% of organisms many countries, it is required that physicians and other
have 2 nuclei); no health care practitioners report sexually transmitted dis-
peripheral chroma- eases (STDs) but this is not always the case. Therefore,
tin; and nuclei com- the rate may be much higher than that reported and there
posed of 5–8 discrete are significant numbers of cases that go undiagnosed.
granules
This organism is found in the urogenital tracts of both
Cytoplasm Indistinct appearance males and females, and humans are the only hosts at this
in stained specimen
time (Figure 3-6). This infection is also concurrent with
Other Features Organism may be the presence of other sexually transmitted diseases, most
found in eggs of
Enterobius vermicu- often with gonorrhea. As listed previously, this organism
laris; does not survive has no cyst stage and is vulnerable to drying out and not
for long following surviving to be transmitted to others when found in body
excretion fluids outside the body, but a few cases have been known
to be transmitted by nonsexual means.
Dientamoeba fragilis
Trophozoite stage Morphology

In females, the diagnosis is generally made by finding the
trophozoite in either the urine or in vaginal discharge.
Men may also produce the trophozoites in urine speci-
mens and in prostatic secretions. The organisms have four
anterior flagella and the cell membrane undulates in those
Delmar/Cengage Learning that are highly motile. Dead or dying trophozoites are

more problematic for visual diagnosis and may be identi-
fied as white blood cells. Therefore, the specimen should
be read microscopically as quickly as possible upon col-
lection of the specimen, as the vitality of the organism
diminishes rapidly in the open air and light. A stained