[Last Modified: ]
[Entamoeba histolytica]

Entamoeba histolytica/Entamoeba dispar trophozoites have a single nucleus, which have a centrally placed karyosome and uniformly distributed peripheral chromatin.  This typical appearance of the nucleus is not always observed as some trophozoites can have nuclei with an eccentric karyosome and unevenly distributed peripheral chromatin.  The cytoplasm has a granular or "ground-glass" appearance.  E. histolytica/E. dispar trophozoites usually measure 15 to 20 µm (range 10 to 60 µm), tending to be more elongated in diarrheal stool.

Erythrophagocytosis (ingestion of red blood cells by the parasite) is the only morphologic characteristic that can be used to differentiate E. histolytica from the nonpathogenic E. dispar.  However, erthrophagocytosis is not typically observed on stained smears of E. histolytica.

A	B

A, B: Trophozoites of E. histolytica/E. dispar stained with trichrome.

C	D

C, D: Trophozoites of E. histolytica.  The specimen was preserved in poly-vinyl alcohol (PVA) and stained with trichrome.  The vacuolated cytoplasm seen in image D may be the result of less than optimal preservation.  PCR was performed on this specimen to differentiate between E. histolytica and E. dispar.

E

E: Trophozoite of E. histolytica/E. dispar, measuring approximately 16.7 µm, stained with trichrome.  The image was taken at 1000× magnification and contributed by the Kansas Department of Health and Environment.