entamoeba histolytica - national university
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Entamoeba histolytica
Protozology (MLS- PROT- 225)
Batch: 10
Hz. Hussien Sharif Siddig
TEL .0912559164
Entamoeba histolytica
• Disease
– Amoebiasis, amoebic dysentery.
• Geographical distribution
– Cosmopolitan, mainly in tropical and subtropical
areas.
• Morphology 1- Trophozoite:
– It is 10-20μm, commensal in large intestine.
– Ectoplasm: well defined hyaline layer.
– Endoplasm: granular cytoplasm
– Nucleus: 3.7μm, spherical
– Containing RBCs.
Trophozoite acts as active motile feeding reproducing stage.
2- Precyst: Trophozoite withdraws its pseudopodia and
becomes rounded and devoid of food inclusions.
3- Cyst: 10-18 μm, nucleus divides twice by mitotic division
to form 4 nucleated cyst (infective stage).
- Habitat: The parasite lives in the large intestinal lumen
mainly caecum and may invade other tissues, reaching the
circulation leading to extra-intestinal lesions.
- Infective stage: 4 nucleated cyst in contaminated food.
- Mode of infection: Ingestion of infective stage.
Life cycle
• Pathology
1. Intestinal amoebiasis:-
• Invasion of the intestinal wall leads to formation
of several flask-shaped ulcers in the colon as
primary lesions.
2. Extraintestinal amoebiasis:
• The lesions are secondary to the primary large
intestinal lesions and may result in hepatic,
pulmonary or cerebral, renal....ect amoebic
abscess.
flask-shaped ulcers
• Clinical manifestations
1) Intestinal:
a) Asymptomatic (cyst passers about 75%)
b) Non dysenteric amoebiasis (chronic
amoebiasis): There is diarrhea, abdominal cramps,
flatulence, nausea, anorexia but no visible blood in the
stool. the diarrhea is alternating with constipation. If
not treated, it may pass to frank dysentery.
c) Dysenteric amoebiasis (Acute amoebiasis): This is found in 5% of infected cases. The number of
stools increases (up to 10 to 20/day), little fecal
material is present, but blood, mucus, and nits of
necrotic tissue. As progresses, there is fever, colic,
vomiting and abdominal tenderness.
1. Extraintestinal amoebiasis:
• The lesions are secondary to the primary
large intestinal lesions and may result in
hepatic, pulmonary or cerebral, renal....ect
amoebic abscess.
• Diagnosis
1) Diagnosis of intestinal amoebiasis:
a) Stool examination: cyst is found in formed stool,
trophozoite in diarrheic stool. Both forms may be found in
soft stools. Examination must be carried out promptly
because most trophozoites die in less than 30 minutes.
b) Culture: Culture on specific media may be used to
increases the number of predicted positive cases.
c) Sigmoidoscopy and biopsy: In mild cases there are
usually no findings. However, characteristic amoebic
lesions may be found in severe cases.
d) Serology: Many tests are available, but their use for
diagnosis of intestinal amoebiasis is limited because
antibody develops only after a significant degree of tissue
invasion. Asymptomatic cysts carriers have negative
serologic tests, unless tests are positive from previous
invasive amoebiasis.
2) Diagnosis of extra-intestinal amoebiasis:
a) Serology: More than 90% of patients have positive
serologic titers.
b) Radiology: May be suggestive specially in hepatic amoebic
abscess.
c) Detecting the parasite: Aspiration of the lesion in selected
cases may be of help.
• Control
1) Food sanitation, sanitary waste disposal & safe water
supply.
2) Treatment of infected cases..
3) Flies control.
4) Food handlers examination.
5) Health education.
Non-pathogenic Amebae
We will examine 3 species in laboratory:
Entamoeba coli
Habitat:
Hosts:
Pathology:
Distribution:
Prevalence in U.S. is estimated at 36 %; prevalence in tropics may be up to 100%
Entamoeba coli life cycle stages
1. TROPHOZOITE - 20 to 30 m in diameter
- granular endoplasm is coarser than E. histolytica
- one nucleus
- lives in large intestine and feeds on bacteria does not invade tissue
Entamoeba coli life cycle stages
2. CYST - encystment is similar to that of E. histolytica
- immature cysts are rare in fecal
smears
- mature cyst is large, 10 to 33 m, has 8 nuclei
- cyst is released in the feces into the external environment
- importance of human infection?
Entamoeba coli life cycle