Intestinal Protozoa
PARASITES
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Intestinal Protozoa
Intestinal Protozoa
Amoeba: Entamoeba histolytica
Diseases: Entamoeba histolytica causes amebic dysentery and liver abscess.
Important Properties: The life cycle has two stages:
the motile (trophozoite)
the nonmotile cyst
is found within the intestinal and found in nondiarrheal stools.
extraintestinal lesions and in diarrheal
stools.
These cysts are killed by boiling but not
by chlorination of water supplies. They
are removed by filtration of water.
The mature trophozoite has a single The cyst has four nuclei, an important
nucleus
with
lining
of
peripheral diagnostic criterion
chromatin and a central nucleolus
(karyosome).
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Intestinal Protozoa
Pathogenesis & Epidemiology:
1. The organism is acquired by ingestion of cysts that are transmitted by the fecal–
oral route in contaminated food and water. Anal–oral transmission, e.g., among male
homosexuals.
2. The ingested cysts differentiate into trophozoites in the ileum but tend to colonize
the cecum and colon.
3.The trophozoites invade the colonic epithelium and secrete enzymes that cause
localized necrosis. As the lesion reaches the muscularis layer, a typical "flaskshaped" ulcer forms.
4. Progression into the submucosa leads to invasion of the portal circulation by the
trophozoites. By far the most frequent site of systemic disease is the liver, where
abscesses containing trophozoites form.
Clinical Findings:
1. Acute amebiasis presents as dysentery (i.e., bloody, mucus-containing diarrhea)
accompanied by lower abdominal discomfort, flatulence, and tenesmus.
2. Chronic amebiasis: diarrhea, weight loss, and fatigue also occur. Roughly 90% of
those infected have asymptomatic infections, but they may be carriers, whose feces
contain cysts that can be transmitted to others. In some patients, a granulomatous
lesion called an ameboma may form in the cecal or rectosigmoid areas of the colon.
These lesions can resemble an adenocarcinoma of the colon.
3. Amebic abscess of the liver is characterized by right-upper-quadrant pain, weight
loss, fever, and a tender, enlarged liver. Right-lobe abscesses can penetrate the
diaphragm and cause lung disease.
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Intestinal Protozoa
Laboratory Diagnosis:
1. Intestinal amebiasis: finding either trophozoites in diarrheal stools or cysts in
formed stools. Diarrheal stools should be examined within 1 hour of collection.
Trophozoites contain ingested red blood cells. Because cysts are passed intermittently,
at least three specimens should be examined.
-E. histolytica can be distinguished by two criteria. (1) The nature of the nucleus of
the trophozoite (has a small central nucleolus and fine chromatin granules along the
border of the nuclear membrane). (2) The second is cyst size and number of its
nuclei.
2. A complete examination for cysts includes a wet mount in saline, an iodine-stained
wet mount, and a fixed, trichrome-stained preparation. These preparations are also
helpful in distinguishing amebic from bacillary dysentery.
3. Serologic testing ex.indirect hemagglutination test.
4. Detects nucleic acids of the organism in a PCR-based assay.
Treatment:
1. The treatment of choice for symptomatic intestinal amebiasis or hepatic abscesses is
metronidazole (Flagyl) or tinidazole.
2. Asymptomatic cyst carriers should be treated with iodoquinol or paromomycin.
Prevention:
1. avoiding fecal contamination of food and water. 2. good personal hygiene such as
hand washing.
3. Purification of water supplies. 4. In areas of endemic infection, vegetables should be
cooked.
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Intestinal Protozoa
Flagellates: Giardia lamblia causes giardiasis.
Important Properties:
The life cycle consists of two stages:
the trophozoite
the cyst
The trophozoite is pear-shaped with two The oval cyst is thick-walled with four
nuclei, four pairs of flagella, and a nuclei and several internal fibers. Each
suction disk with which it attaches to the cyst gives rise to two trophozoites
intestinal wall
during excystation in the intestinal tract.
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Intestinal Protozoa
Pathogenesis & Epidemiology:
1.The organism is found worldwide. In addition to being endemic, giardiasis
occurs in outbreaks related to contaminated water supplies. Chlorination does not
kill the cysts, but filtration removes them.
2.Many species of mammals as well as humans act as the reservoirs. They pass
cysts in the stool, which then contaminates water sources. Giardiasis is common in
male homosexuals as a result of oral-anal contact.
3.Transmission occurs by ingestion of the cyst in fecally contaminated food and
water.
4.Excystation takes place in the duodenum, where the trophozoite attaches to the
gut wall but does not invade. The trophozoite causes inflammation leading to
malabsorption of protein and fat.
Clinical Findings:
Watery (nonbloody), foul-smelling diarrhea is accompanied by nausea,
anorexia, flatulence, and abdominal cramps persisting for weeks or months. There
is no fever.
Laboratory Diagnosis:
-Finding trophozoites or cysts or both in diarrheal stools.
-In formed stools, e.g., in asymptomatic carriers, only cysts are seen.
-An ELISA test that detects a Giardia cyst wall antigen in the stool
-If microscopic examination of the stool is negative, the string test.
Treatment:
The treatment of choice is metronidazole (Flagyl) or quinacrine hydrochloride.
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Intestinal Protozoa
Prevention:
Prevention involves drinking boiled, filtered, or iodine-treated water in endemic
areas.
Chilomastix mesnili
A non-pathogen - must be differentiated from Giardia. Found in cecum and colon.
Transmission occurs by ingestion of mature cysts.
Morphology
 Trophozoite - 4 flagella (3 anterior, 1 associated with the cytostome; one
nucleus, always located anteriorly.
 Cyst - lemon shape; 1 nucleus; cytostome may be seen.
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Intestinal Protozoa
Balantidium coli (ciliates)
Balantidium coli, the cause of balantidiasis or balantidial dysentery, is the largest
intestinal protozoan of humans.
Morphology & Identification:
The trophozoite is a ciliated, oval organism. The cell wall is lined with spiral rows
of cilia. The cytoplasm surrounds two contractile vacuoles, food particles and
vacuoles, and two nuclei—a large, kidney-shaped macronucleus and a much
smaller, spherical genetic micronucleus. The macronucleus, contractile vacuoles,
and portions of the ciliated cell wall may be visible in the cyst.
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Intestinal Protozoa
Pathogenesis, Pathology, & Clinical Findings:
1.When cysts are ingested by the new host, the cyst walls dissolve and the released
trophozoites descend to the colon, and form cysts that pass in the feces.
2.However, rarely, the trophozoites invade the mucosa and submucosa of the large
bowel and terminal ileum. As they multiply, abscesses and irregular ulcerations
are formed.
3.Chronic recurrent diarrhea, is the most common clinical manifestation, but there
may be bloody mucoid stools, tenesmus, and colic.
Diagnostic Laboratory Tests:
1.laboratory detection of trophozoites in liquid stools or cysts in formed stools.
2.Sigmoidoscopy may be useful for obtaining material directly from ulcerations for
examination.
Treatment:
A course of oxytetracycline may be followed by iodoquinol or metronidazole if
necessary.
Epidemiology:
-B coli is found in humans throughout the world, particularly in the tropics.
- Pig farmers and slaughterhouse workers are particularly at risk, though poor
sanitation and crowding in jails, mental institutions are associated with infection.
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