Dientamoeba fragilis
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Dientamoeba fragilis is a type of amoeboid that has been known to cause symptoms in some of the people who have this parasite. In 1970 H. Steinitz, a gastroenterologist in Israel, did a study trying to find out why the symptoms from this amoeba recurred even after treatment. He determined that the amoeba had truly never left. In order to ascertain that it has truly been eliminated from the body completely, a stool culture must be done only after a purgative such as MgSO4 is administered or better yet a rectoscopy is completed.
The complete life cycle of this parasite has not yet been determined, but assumptions were made based on clinical data. To date, the cyst stage has not been identified in D. fragilis life cycle, and the trophozoite is the only stage found in stools of infected individuals . D. fragilis is probably transmitted by fecal-oral route and transmission via helminth eggs (e.g., Ascaris, Enterobius spp.) has been postulated . Trophozoites of D. fragilis have characteristically one or two nuclei (, ), and is found in children complaining of intestinal (e.g., intermittent diarrhea, abdominal pain) and other symptoms (e.g., nausea, anorexia, fatigue, malaise, poor weight gain).
Dientamoeba fragilis is described as a trichomonad that replicates by binary fission, and moves by pseudopodia. The cytoplasm typically contains numerous vacuoles, which at times may contain ingested debris, including bacteria. D. fragilis possesses similar flagellate characteristics. In a binucleate form there is a spindle structure located between the nuclei, which stems from certain polar configurations adjacent to a nucleus—these configurations appear to be homologous to hypermastigotes’ atractophores. There is a complex Golgi system; the nuclear envelope has two membranes, and the nuclear structure of D. fragilis is more similar to that of flagellated trichomonads than to that of Entamoeba. Also noted, is the presence of round inclusions that eventually were determined to be hydrogenosomes. D. fragilis mode of feeding is phagocytosis. Waste materials are eliminated from the cell through digestive vacuoles by exocytosis.
[edit] Clinical Features
Symptoms that have been associated with infection include diarrhea, abdominal pain, anorexia, nausea, vomiting, fatigue, and weight loss.
[edit] Laboratory Diagnosis
Infection is diagnosed through detection of trophozoites in permanently stained fecal smears (e.g., trichrome). This parasite is not detectable by stool concentration methods. Dientamoeba fragilis trophozoites can be easily overlooked because they are pale-staining and their nuclei may resemble those of Endolimax nana or Entamoeba hartmanni.
Diagnostic findings
- Microscopy
- Morphologic comparison with other intestinal parasites
Treatment: Safe and effective drugs are available. The drug of choice is iodoquinol. Paromomycin*, tetracycline*, (contraindicated in children under age 8, pregnant and lactating women) or metronidazole can also be used.
