Clinical Pathology: Microbiology

784) A 4-year-old girl presented to her pediatrician with a 1-week history of abdominal pain and increased bowel movements producing greenish-brown, watery diarrhea. Several children attending her day care center were experiencing similar symptoms. Which one of the following is the etiologic agent shown in the figure?

• The life cycle of Dientamoeba fragilis does not include a cyst stage. The morphology of D. fragilis can be differentiated from that of Giardia intestinalis, as described in the table.

• The mode of transmission is through fecal-oral spread and sometimes through coinfected eggs of Enterobius vermicularis (pinworm).

• Disease is more common in children; adults are typically asymptomatically colonized.

• Examination of a single stool sample has a sensitivity of 50%; multiple samples (up to 6) are necessary to optimize detection.

• Common treatment strategies for D. fragilis infection include metronidazole, iodoquinol, and paromomycin.

Helminth Characteristics
Giardia intestinalis Dientamoeba fragilis
Shape Pear shaped Ameboid
Size 10-20 μm long,
5-15 μm wide
5-15 μm
Nuclei (#) 2 1-2
Peripheral chromatin Yes No
Median bodies (#) Yes (2) No
Flagella (#) Yes (4 pair) No
Sucking disc Yes No

* = Required 
* Note Title
* Note