Entamoeba histolytica Schaudinn, 1903 (Emended Walker, 1911)

Morphological Characters in vivo:
Trophozoites ranging in size from 20 to 40 µm in diameter. Locomotion rapid, gliding, by means of a single well defined pseudopodium, often extended explosively, without conspicuous differentiation between ecto- and endoplasm. Cytoplasm with a single nucleus, rarely up to four; often with ingested red blood cells, sometimes with leukocytes, or bacteria; rich in glycogen; with ribosomes arranged in helices which aggregate to form characteristically shaped elongate bars with rounded ends (=chromatoid bodies). Without classical mitochondria, rough endoplasmic reticulum, or golgi apparatus. Nucleus vesicular, spherical, measuring 4 to 7 µm in diameter, consisting of a delicate achromatic membrane lined usually by a single layer of small chromatin granules, uniform in size, in contact or very close to each other. With a small spherical karyosome (0.5 µm in diameter), often centrally located, surrounded by an achromatic capsule-like structure.

Cysts spherical, measuring 10 to 16 µm in diameter; with four nuclei when mature, rarely up to eight; with glycogen in a distinct vacuole in the immature cyst, becoming more diffuse as the cyst matures; often with chromatoid bodies in the immature cyst, disappearing as the cyst matures. Nuclei with morphology similar to those of trophozoites.

Geographic Distribution:
Worldwide

Hosts:
Humans, several nonhuman primates, cats, dogs and rats are well documented hosts. Reports of infection in other mammals must be viewed with caution unless evidence of tissue invasion has been provided, and/or the parasite has been isolated and subjected to isoenzyme or other discriminatory analysis.

Phylogeny:
The relationships of E. histolytica to other species of Entamoeba and to other eukaryotes are shown here.

This description is taken from:

Diamond, L.S. & Clark, C.G. (1993) A redescription of Entamoeba histolytica Schaudinn, 1903 (Emended Walker, 1911) separating it from Entamoeba dispar Brumpt, 1925. J. Euk. Microbiol. 40: 340-344.

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