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