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Entamoeb

Disease. amebiasis, amebic dysentery, amebic hepatitis

Geographic distribution. Worldwide in temperate and tropic zone.

Geographic distribution. Worldwide in temperate and tropic zone.

Geographic distribution. Worldwide in tropical and temperate zone

Infection rate. Less than 10% through out the world.

Infection rate. Not clear.

Infection rate. The actual incidence of amebiasis in the worldwide remains unknown. Survey indicate that the infection rates vary from 0.2 to 50%, being directly correlated with sanitary conditions.

Life cycle. Same as that of E. histolytica.

Life cycle. Human is the principal host and the source of infection. The infective cysts pass out through the feces, and are immediately infective. Cyst-contaminated food or water cause infections. Excystment takes place in the lower part of the small intestine. The immature amebas move downward to the large intestine, where they establish a site of infection. Reproduction occurs by binary fission.

Morphology. Trophozoite is measured 15 to 50 ㎛ in diameter and has a large karyosome, frequently with irregular shape and eccentric in nucleus. Cysts overlap the size range of E. histolytica, being 10 to 35 ㎛ in diameter. One to eight nuclei including the eccentric location of the karyosome are observed.

Morphology. Trophozoite is smaller than E. histolytica, ranged 5 to 12 ㎛ in diameter, and has a large karyosome, frequently irregular nucleus. Cysts overlap the size range of E. hartmanni, being 8 to 9 ㎛ in diameter. One to four nuclei including the large karyosome are observed.

Morphology. The majority of trophozoites measure from 15 to 30 ㎛. The hyaline ectoplasm, sharply separated from the endoplasm, constitutes about one-third of the entire trophozoite. The thin, fingerlike ectoplasmic pseudopodia are extended rapidly. Hematoxylin staining reveals a nuclear membrane, the inner surface of which is lined with uniform chromatin. The small, deeply staining karyosome is centrally located. The round or oval cysts measure 10 to 20 ㎛ in diameter, and contain one to four nuclei and sausage-shaped chromatoid bodies.

Pathology and clinical symptoms. Non-pathogenic.

Pathology and clinical symptoms. Non-pathogenic amoeba.

Pathology and clinical symptoms. The lesions produced by E. histolytica are primarily intestinal, and secondarily extraintestinal. The intestinal lesions are confined to the large intestine, frequently cecal and sigmoidorectal regions. The typical flask-like primary ulcers to large necrotic areas are produced. In acute amebiasis, there is severe dysentery with numerous small stools containing blood, mucus and necrotic mucosa accompanied by acute abdominal pain, tenderness and fever. Chronic amebiasis is characterized by recurrent attacks of dysentery with gastrointestinal disturbance. In extraintestinal amebiasis, the liver is invaded chiefly, resulting amebic hepatitis or liver abscess. It is characterized by an enlarged, tender liver, with pain in the upper right hypochondrium. Less frequently, lung abscess, splenic abscess, brain abscess or cutaneous amebic lesions are seen.

Diagnosis. Detection of cysts in the stool.

Diagnosis. Detection of cysts in the stool.

Diagnosis. Diagnosis may be made by the microscopic identification of cysts in solid feces or trophozoites in diarrheic stool. The parasite may be detected in aspirated material of liver abscess. Serologic tests, such as IFA, ELISA, for specific antibodies to E. histolytica are very helpful in diagnosis of invasive amebiasis.

Prevention. Environmental sanitation is necessary to prevent water and food contamination. Boiling or filtration of drinking water is a safe and effective way of prevention, and avoidance of consuming contaminated food is essential.

Comments. This amoeba must be differentiated from E. histolytica.

Ho-Joon Shin

Comments. This amoeba must be distinguished from E. histolytica.

Ho-Joon Shin

Comments. There is a non-pathogenic E. dispar, having a same morphology with E. histolytica. It can be distinguished by molecular biological techniques such as PCR.

Tai Soon Yong


Cyst of Entamoeba histolytica, 5-20 ㎛ in size. Chromatoid bodies are often present with thick rodlike masses. The number of nuclei is 1-4.

Tai Soon Yong


Cyst of Entamoeba histolytica showing a large nucleus with centrally located small karyosome (I-H stain, 1000 x).

DY Min/MH Ahn/JS Ryu


Cyst of Entamoeba coli showing 7 nuclei (Iodine stain, 1000x).
B. Cyst of Entamoeba coli showing 7 nuclei (I-H stain, 1000x).

DY Min/MH Ahn/JS Ryu


Cyst of Endolimax nana showing 2 nuclei with large karyosome (I-H stain, 1000x).

DY Min/MH Ahn/JS Ryu


Cyst of Iodamoeba butschlii showing a large glycogen vacuole (I-H stain, 1000x).

DY Min/MH Ahn/JS Ryu


Trophozoite stage from culture of Entamoeba histolytica. The living trophozoites vary in size from about 10 to 60 um in diameter, depending on their degree of activity and various other conditions. The nucleus is spherical, with a diameter about one-fifth or one-sixth
that of the entire ameba. It contains a small, distinct central karyosome surrounded by an unstained "halo". Iron-Hematoxylin stain x400

Hae-Seon Nam


Live trophozoites of Entamoeba histolytica. Note the extending pseudopodia from the ectoplasm.

Tai Soon Yong


Cultured Entamoeba histolytica trophozoite.

Tai Soon Yong


Trophozoite of Entamoeba histolytica. The nucleus is characterized by the presence of a small, compact, centrally located karyosome (I-H stain, 1000 x). B. Cultured trophozoite shows pseudopodia.

DY Min/MH Ahn/JS Ryu


Amebic appendicitis in human. H&E, X400.

Duk-Young Min


Amebic liver abscess in human. H&E, X100.

Duk-Young Min


Amebic liver abscess in human. Trophozoites of Entamoeba histolytica are well observed. H&E, X400.

Duk-Young Min


Amebic colon abscess in human. H&E, X40.

Duk-Young Min


Amebic colon abscess in human. H&E, X100.

Duk-Young Min


Amebic colon abscess in human. Trophozoites of Entamoeba histolytica can be distinguished from necrotic tissues. H&E, X400.

Duk-Young Min


Amebic lung abscess in human. H&E, X100.

Duk-Young Min


Amebic lung abscess in human. Trophozoites of Entamoeba histolytica are well observed in necrotic tissues. H&E, X400.

Duk-Young Min


Experimental liver abscess formation following intraperitoneal injection of Korean strain (YS-27) of Entamoeba histolytica in a Mongolian gerbil.
(A) A liver abscess showing an area of necrosis,
(B) An magnified view of necrotic region. Note the presence of Entamoeba histolytica trophozoites.

Tai Soon Yong


Entamoeba histolytica in intestine, Trichrome stain(A).

DY Min/MH Ahn/JS Ryu


Trophozoite of Entamoeba histolytica in intestine. Nuclei with typical central karyosome are visible (H&E, 1000x).

DY Min/MH Ahn/JS Ryu