Dientamoeba fragilis

D. fragilis
Phase contrast x 400

D. fragilis is a flagellate, formerly considered an amoeba. Usual range in size is 9-12 mm.

It has no evident flagella and exists in the trophozoite stage only (shown on the right).

It contains one or two nuclei which can be seen in both stained or unstained preparations.

One nucleus is seen in 40% of the organism and the karyosome usually is fragmented into 4-8 segments, as shown on the left.

Uninucleate trophozoites are more difficult to identified than the binucleate form (shown below) because they can be easily confused with other small nonpathogenic Entamoeba like Endolimax nana.

D. fragilis
Trichrome Stain x 1000

There are no peripheral chromatin on the nuclear membrane, and a horizontal line connecting both nuclei is usually quite evident.

The cytoplasm may be finely to heavily granular and may be vacuolated.

One of the difficulties in diagnosing Dientamoeba infection is the fact that it often stain pale so that it blends in well with the background fecal material.

Unless the reader continually uses the fine adjustment these organism can easily be missed.