Page 435 - Review of Medical Microbiology and Immunology ( PDFDrive )

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51
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Intestinal &

Urogenital—Protozoa

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CHAPTER C ONTENT S

Introduction
INTESTINAL PROTOZOA
Trichomonas
Self-Assessment Questions
Entamoeba
Summaries of Organisms
Giardia
Cryptosporidium
Practice Questions: USMLE & Course Examinations
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INTRODUCTION
important opportunistic lung pathogen Pneumocystis will
In this book, the major protozoan pathogens are grouped
be discussed in this group, although there is molecular evi-
according to the location in the body where they most fre-
dence that it should be classified as a fungus.
quently cause disease. The intestinal and urogenital proto-
The major and minor pathogenic protozoa are listed in
zoa are described in this chapter, and the blood and tissue
Table 51–1.
protozoa are described in Chapter 52.
Although immigrants and Americans returning from
(1) Within the intestinal tract, three organisms—the ameba
abroad can present to physicians in the United States with
Entamoeba histolytica, the flagellate Giardia lamblia, and the
any parasitic disease, certain parasites are much more likely
sporozoan Cryptosporidium hominis—are the most important.
to occur outside the United States. The features of the
(2) In the urogenital tract, the flagellate Trichomonas
medically important protozoa, including their occurrence
vaginalis is the important pathogen.
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(3) The blood and tissue protozoa are a varied group
The medically important stages in the life cycle of the
consisting of the flagellates Trypanosoma and Leishmania
intestinal protozoa are described in Table 51–3.
INTESTINAL PROTOZOA
ENTAMOEBA
in nondiarrheal stools. These cysts are not highly resistant
and are readily killed by boiling but not by chlorination of
Diseases
water supplies. They are removed by filtration of water.
The cyst has four nuclei, an important diagnostic crite-
Entamoeba histolytica causes amebic dysentery and liver
rion. Upon excystation in the intestinal tract, an ameba
abscess.
with four nuclei emerges and then divides to form eight
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trophozoites. The mature trophozoite has a single nucleus
Important Properties
with an even lining of peripheral chromatin and a promi-
nent central nucleolus (karyosome).
The life cycle of E. histolytica is shown in Figure 51–1. The
Antibodies are formed against trophozoite antigens in
life cycle has two stages: the motile ameba (trophozoite) and
the nonmotile cyst (Figures 51–2A and B, 51–3, and 51–4).
The trophozoite is found within the intestinal and extraint-
infection does not prevent reinfection. The antibodies are
estinal lesions and in diarrheal stools. The cyst predominates
useful, however, for serologic diagnosis.
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