This document summarizes four intestinal parasites: Entamoeba histolytica, Balantidium coli, Trichomonas vaginalis, and Giardia lamblia. It describes their classification, transmission, sites of infection, clinical manifestations, and laboratory diagnosis. Entamoeba histolytica can cause intestinal or extra-intestinal amoebiasis by forming ulcers in the intestine or other organs. Balantidium coli causes colitis and other infections of the large intestine. Trichomonas vaginalis causes vaginitis or urethritis through sexual contact. Giardia lamblia causes giardiasis through a fecal-oral route and leads to diarrhea and malabsorption.

1. Entamoeba, Balantidium,
Trichomonas & Gardia
Aman Ullah
B.Sc. MLT
M. Phil Microbiology
Master in Health Research
Certificate in Health Professional Education

2. Entamoeba histolytica
Classification: Protozoan-Rhizopod-Amoeba
Host: Homo sapiens
Transmission: Faecal-oral (alimentary)
Infective stage: Mature cyst
Localisation: Large intestine
Pathogenicity:
1) Intestinal amoebiasis (Amebic dysentery): formation of ulcerus of the wall of the
intestine, acute or chronic diarrhoea, stool containing blood and mucus; may be
asymptomatic infection.
2) Extra- intestinal amoebiasis: abscess of liver, lung, brain, skin.
Laboratory diagnosis: Fresh stools are examined under the microscope. E. histolytica
(cysts with 4 nuclei) can be demonstrated in the stools.

3. Life cycle
Cyst: infective
stage
Inters mouth through
contaminated food, drink,
fly, or through using human
stool as fertilizer
To L.I. lumen and change
into trophozoite
(pathogenic stage)
Produce lytic enzymes
(capable of doing lysis
and produce ulcer)Flask shape
ulcer
Can do
erosion
through B.V.
to liver and
other organs

4. Balantidium coli
Classification: Protozoan-Ciliate
Disease: Balantidiasis
Geographical distribution: Cosmopolitan.
Hosts: Man, domestic pig
Transmission: Faecal-oral (alimentary)
Localisation: Large intestine
Clinical Manifestations: Colitis, ulcers and abscesses of colon,
diarrhoea, blood and mucus in the stool.
Laboratory diagnosis: Microscopic examination of the faeces.

5. Trichomonas vaginalis
Classification: Protozoan-flagellates-urogenital
Disease: Urogenital trichomoniasis
Geographical distribution: cosmopolitan
Host: man
Transmission: by sexual contact; otherwise (through contact with toilet seats and
towels, for example)
Localisation: vagina, urethra, prostate
Clinical Manifestations: vaginitis in women, more commonly asymptomatic in men,
but may lead to prostatitis or urethritis. The main symptoms are dysuria, pruritis,
yellow and frothy discharge
Laboratory diagnosis: microscopic examination of the vaginal fluid, scrapings, or
washing

6. Giardia
Disease: Giardia lamblia causes giardiasis.
Important Properties: Life cycle consists of two stages: the trophozoite and
the cyst
Transmission: Fecal-oral route
Distribution: Cosmopolitan
Pathogenesis: Excystation takes place in the duodenum, where the
trophozoite attaches to the gut wall but does not invade the mucosa and does
not enter the blood stream. The trophozoite causes inflammation of the
duodenal mucosa, leading to malabsorption of protein and fat.
Approximately half of those infected are asymptomatic carriers who continue
to excrete the cysts for years.

7. Giardia
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: Diagnosis is made by finding
trophozoites or cysts or both in diarrheal stools. An
ELISA test that detects a Giardia cyst wall antigen in
the stool is also very useful

8. Questions/Suggestions
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