Parasitology
Faculty: AGUAZIM SAMUEL M.D.
Lange chapter 51
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Intestinal and Urogenital
Protozoa
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Parasites occur in two distinct forms:
• Single-cell called protozoa
• Multicellular metazoa called helminths
or worms.
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Protozoa can be subdivided into four
groups:
•
•
•
•
Sarcodina (amebas),
Sporozoa (sporozoans),
Mastigophora (flagellates),
Ciliata (ciliates)
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Metazoa are subdivided into two phyla:
•Platyhelminthes
(flatworms)
•Nemathelminthes(roundworms,
nematodes).
•Platyhelminthes
contains two medically
important classes:
•Cestoda
(tapeworms) (swimming in a cespool
of tapeworms)
•Trematoda
(flukes). (It is a fluke that you won a
million dollars and you are trembling with
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excitement)
Intestinal Protozoa
•
Within the intestinal tract, three organisms:
- The ameba (Entamoeba histolytica)
- The flagellate (Giardia lamblia)
- The sporozoan (Cryptosporidium parvum)
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Urogenital Protozoa
•
In the urogenital tract, one organism:
- The flagellate (Trichomonas vaginalis).
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CASE
• 33 year old man, presenting with right
upper quadrant pain and fever of 4 days
duration; slight yellowing of skin.
• 1 week before, he had bloody stools,
about 3 or 4 times per day, but it resolved
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Case: 5 cm hypoechoic liver
mass
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CASE
• Metronidazole
• Significant improvement after 7 days
• Repeat UTZ: smaller mass
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CASE
• Impression: Amebic liver abscess,
secondary to Entamoeba histolytica
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Intestinal Protozoa
Entamoeba histolytica
• Diseases:Amebic dysentery and liver
abscess.
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Entamoeba histolytica
Characteristics: Intestinal protozoan. The life
cycle consists of two stages:
(1) Motile ameba (trophozoite) consists of
one ingested red blood cell and one nucleus
(2) Non-motile cysts with four nuclei with no
internal fiber.
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Trophozoite: one ingested red blood cell and one nucleus
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Cysts: four nuclei with no internal fiber
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Entamoeba histolytica trophozoites in section of intestine (H&E)
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Entamoeba histolytica cyst and trophozoite, haematoxylin stained
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Entamoeba histolytica
• Life cycle: Humans ingest cysts, which form excystation in
small intestine, which form trophozoites. Trophozoites pass to
the colon and multiply. Cyst form in the colon.
• Transmission and Epidemiology: Fecal-oral transmission of
cysts via water, fresh fruit and vegetables. Human reservoir.
Occurs worldwide, especially in tropics.
• Also: ano-genital or oro-anal sexual contact
•
Pathogenesis:
Trophozoites invade colon epithelium and produce “teardrop”
ulcer. Can spread to liver and lungs and cause abscess.
Excystation: the action of an encysted organism in escaping from its19
envelope
Life cycle of Entamoeba histolytica
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Histopathology of a typical flask-shaped ulcer of intestinal amebiasis. CDC
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Amebic dysentery
 Acute amebiasis
frequent dysenteric stools of pus and
blood ; without feces
systemic toxicity: fever, dehydration,
electrolyte abnormalities
Tenesmus , abdominal tenderness
 Chronic amebiasis
recurrent episodes of dysentery
intervening GIT disturbances, constipation
 Invasive disease: liver, lung and brain
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AMEBOMA
• proliferative
granulomatous
response at an ulcer
site
• infectious
pseudotumor
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Ameboma
leading point of an
intussusception
or may cause intestinal
obstruction
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Amebic liver abscess
• Most common extraintestinal form
• metastasis from intestinal infection
• Symptomatic intestinal infection need not be
present
• right upper quadrant pain
• right shoulder pain
• presses on the common bile duct : jaundice
• Lung atelectasis, consolidation, pleural effusion
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Gross pathology of liver containing amebic abscessGross. CDC
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RUPTURED AMEBIC LIVER ABSCESS WITH
“ANCHOVY PASTE”
Gross pathology of amebic abscess of liver. Tube of "chocolate" pus from
abscess.
CDC
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Amebiasis cutis
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Brain abscess
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Entamoeba histolytica
Laboratory Diagnosis:
1. Trophozoites or cysts visible in stool.
2. Serologic testing (indirect hemagglutination test
positive with invasive disease).
Treatment:
- Metronidazole plus iodoquinol.
GET BAC on the Metro (Giardia, Entamoeba, Trichomonas,
Bacterial vaginitis, amoebic infection, C. difficile)
Prevention:
1- Proper disposal of human waste.
2- Water purification.
3- Hand washing.
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Giardia lamblia
Most prevalence enteric parasite in the us
Leading in infectious agent in water borne
outbreaking diarrhea
Disease: Giardiasis, especially diarrhea
-Characteristics: Intestinal protozoan.
The life cycle consists of two stages:
(1) Trophozoite, Pear-shaped with two nuclei and four pairs of
flagella.
(2) The oval cyst with four nuclei and several internal fibers34.
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Trophozoite: Pear-shaped with two nuclei and four pairs of flagella
Oval cyst: four nuclei and several internal fibers.
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Giardiasis
 Early symptoms:
flatulence
abdominal distension
nausea
foul-smelling bulky, often watery, diarrhea
explosive!!!
 chronic stage
vitamin B12 malabsorption
disaccharidase deficiency
lactose intolerance
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Diagnosis
 Definitve tests:
Cysts in the stool
Trophozoites in the
duodenum
 (Enterotest®)- string test
 Endoscopy
 Treatment
Metronidazole
4-6 hours
Bile-stained
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Giardia lamblia
• Life cycle: Humans ingest cysts – form trophozoites in
duodenum which encyst and are passed in feces.
• Transmission and Epidemiology: Fecal-oral transmission of
cysts. Human and animal reservoir. Occurs worldwide.
• Pathogenesis: Trophozoites attach to wall with no invasion.
They interfere with absorption of fat and protein.
• Laboratory Diagnosis: Trophozoites or cysts visible in stool.
String test used if necessary.
• Treatment:
Quinacrine, with Metronidazole as an
acceptable alternative..
•
Prevention: Water purification. Handwashing.
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Cryptosporidium parvum
• Disease: Cryptosporidiosis, especially
diarrhea.
• Characteristics: Intestinal protozoan.
• Life cycle: Oocysts release sporozoites; they
form trophozoites. After schizonts and
merozoites form, microgametes and
macrogametes are produced; they unite to
form a zygote and then an oocyst.
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Cryptosporidium parvum
• Transmission and Epidemiology: Fecal-oral
transmission of cysts from undercook meat and
contaminated water. Human and animal reservoir.
Occurs worldwide.
• Pathogenesis: Trophozoites attach to wall of small
intestine but do not invade.
• Laboratory Diagnosis: (round) Oocysts visible in
stool with acid-fast stain.***
• Treatment and Prevention :
None.
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CASE
• 23 year old female, with pain during sexual
contact, copious, malodorous vaginal
discharge of 3 days duration.
• Mild hypogastric pain, no vaginal bleeding
• Regular periods
• Multiple sexual partners, uses OCP
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Case: Strawberry cervix, frothy
discharge,
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Case: vaginal smear
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Case: vaginal smear
• Impression: Trichomoniasis, secondary to
Trichomonas vaginalis
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Urogenital Protozoa
Trichomonas vaginalis
• Disease: Trichomoniasis.
• Characteristics:
Urogenital protozoan. Pear-shaped,with a central
nucleus and four anterior flagella. It exists only as a
trophozoites. No cysts or other forms.
Mot : trophozoites, sexual, formites
• Laboratory Diagnosis: motile Trophozoites visible in
vaginal and prostate secretions.
• Clinical Finding: A watery, foul-smelling, yellowgreenish vaginal discharge accompanied by itching
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and burning occurs.
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Trophozoites: pear-shaped, a central nucleus and four flagella.
Trichomonas - Stained vaginal secretion
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Trichomonas vaginalis
Trichomoniasis
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Trichomoniasis
• Men: asymptomatic
OR
urethritis, prostatitis
• Women: asymptomatic
OR
mild to severe vaginitis
copious yellowish, frothy discharge
strawberry cervix “colpitis macularis”
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Trichomoniasis
• Risk factors
– Infection with other STDs,
especially gonorrhea
– Four or more lifetime sex partners
– Sexual contact with an infected partner
– Not using barrier contraception
– Trading sex for money or drugs
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T. vaginalis - Vaginal discharge
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Trichomonas vaginalis
• Treatment: Metronidazole for both sexual
partners.
• Prevention: Condoms limit transmission
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Isospora belli
ISOSPORIASIS
Transient diarrhea in healthy pts and
severe in IC
Forms and transmission
Fecal oral ingestion of oocysts.
Pathogenesis: The oocysts excyst in the
upper small intestine and invade the
mucosa, causing destruction of the
brush border.
Dx: ACID FAST & ELLIPTICAL
OOCYSTS
RX: TMP-SMX OR
PYRIMETHAMINE/SULFADIAZINE
Note: causes malabsoption similar to
giardia
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CYCLOSPORA CAYETANENSIS
• MILD WATERY
DIARRHEA IN HEALTHY
AND SEVERE IN IC
• Member of
coccida(subtype of
sporozoa)
• TRANSMISSION: fecal
oral(via contaminated
water)
• Dx;spherical oocysts in
modified acid fast stain of a
stool sample
• Rx:trimethoprim
sulfamethoxazole.
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MICROSPORIDIA
• Characterized by obligate
intracellular replication and
spore formation
• Persistent diarrhea in AIDS
pts(Enterocytozoon bieneusi
and Septata intestinalis)
• Tx: fecal oral
• Dx: spores in stool
• Rx: albendazole
• Others: no proven treatment
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Balantidium coli
• only ciliated protozoan that
causes human disease, ie,
diarrhea.
• hosts: cows, pigs and horses
farm work, rural dwellers.
• MOT: ingestion of cysts
• similar to entamebiasis (extraintestinal
lesions do not occur)
• liver, lung and brain abscesses are not seen.
• Diagnosis is made by finding large ciliated
trophozoites or large cysts with a
characteristic V-shaped nucleus in the stool.
• The treatment of choice is tetracycline.
Prevention consists of avoiding
contamination of food and water by
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Simply keep a place
within you where it is
welcomed, and happiness
will come and abide with
you forever.!!!!!!!!!!!!!
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