A 12 year old girl who recently emigrated from Nepal was seen in clinic to establish care. She was entirely asymptomatic. Stool ova and parasite exam was performed and on the permanent trichrome-stained section, the following parasites were identified.
The first image (A) is morphologically diagnostic for Dientamoeba fragilis trophozoites. They are approximately 10 microns in diameter and have 1-2 nuclei, which appear fractured. The next two images are diagnostic for Endolimax nana cysts (B) and trophozoites (C). The cysts are approximately 7 microns in diameter and most have 4 nuclei with blot-like karyosomes that are red on trichrome stain with clearing around the nuclei. The trophozoites are approximately 10 microns in diameter with a single large blot-like karyosome that is red on trichrome stain. The last two images are diagnostic for Entamoeba coli cysts (D) and trophozoites (E). The cysts are approximately 20 microns in diameter and have five to eight nuclei with karyosomes that are red on trichrome stain. The trophozoites are approximately 22 microns in diameter and have a single nucleus with a large kayosome that is darkly staining on trichrome stain. There is peripheral chromatin that is ring-like or clumped.
Dientamoeba fragilis, an ameboflagellate, is a potential pathogen that can be associated with diarrhea, vomiting, abdominal pain, and anorexia, particularly in children. Transmission is via ingestion of contaminated food and water. Some studies postulate co-transmission via helminth eggs, particularly with Enterobius vermicularis. Historically, this intestinal parasite is only known to have a trophozoite form. However, there are now case reports describing the presence of cysts and precysts in humans.1 Treatment is with metronidazole or paromomycin in patients who are symptomatic.
Endolimax nana and Entamoeba coli are protozoa that are considered non-pathogenic and therefore no treatment is necessary. However, when identified, they should be reported since their presence indicates exposure to contaminated food and water. Transmission is via ingestion of cysts. Once in the small bowel, they ex-cyst and migrate to the large bowel where they divide by binary fission and produce cysts. Both cysts and trophozoites are passed in stool.
- Stark D, Garcia LS, Barratt JLN, Phillips O, Roberts T, Marriot D, Harkness J, Ellis JT. Description ofDientamoeba fragilis cyst and precystic forms from human samples. Journ Clin Micro. 2014; 52: 2680-2683.
-Joanna Conant, MD is a 4th year anatomic and clinical pathology resident at the University of Vermont Medical Center.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.