Dientamoeba fragilis

Dientamoeba fragilis
Scientific classification
Domain: Eukaryota (unranked) Excavata Phylum: Metamonada Class: Parabasalia Order: Trichomonadida Genus: Dientamoeba Species: D. fragilis
Binomial name
Dientamoeba fragilis

This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Dientamoebiasis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Dientamoeba fragilis is a single celled parasite that infects the gastrointestinal tract of humans. Trophozoites of D. fragilis characteristically have two nuclei, hence the 'DI' prefix to the genus name. However, the rest of the genus name indicates that it is an ENTeric AMOEBA and not that it is related to intestinal parasites of the genus Entamoeba. The species name refers to the fact that the trophozoite stages are fragile - they do not survive long in the stool after leaving the body of the human host.

Dientamoebiasis

Infection with Dientamoeba fragilis is called Dientamoebiasis and is associated variously with symptoms of abdominal pain, diarrhea, weight loss, and fever.

Phylogenetics

Dientamoeba fragilis is a type of trichomonad. Trichomonads are flagellated organisms but D. fragilis lacks flagella, having secondarily 'lost' them over evolutionary time. Thus, it is an amoeba of flagellate ancestry.

Life Cycle

The life cycle of this parasite has not yet been completely determined, but some assumptions have been made based on clinical data. To date, a cyst stage has not been identified in D. fragilis, and the trophozoite is the only stage found in stools of infected individuals. Like other intestinal parasites, D. fragilis is probably transmitted by the fecal-oral route. In the absence of a cyst form, transmission via helminth eggs (e.g., Ascaris, Enterobius spp.) has been postulated. The rationale for this suggestion is that D. fragilis is closely related to the turkey parasite Histomonas, which is known to be transmitted via the eggs of the helminth Heterakis.

Microbiology

Dientamoeba fragilis replicates by binary fission and moves by pseudopodia. D. fragilis feeds by phagocytosis. The cytoplasm typically contains numerous food vacuoles that contain ingested debris, including bacteria. Waste materials are eliminated from the cell through digestive vacuoles by exocytosis. D. fragilis possesses some flagellate characteristics. In the 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 apparatus; the nuclear structure of D. fragilis is more similar to that of flagellated trichomonads than to that of Entamoeba. Also notable is the presence of hydrogenosomes, which are also a characteristic of other trichomonads.

Treatment

Antimicrobial Regimen

• Dientamoeba fragilis infection

• Preferred regimen: Iodoquinol 650 mg PO tid for 20 days
• Alternative regimen (1): Tetracycline 500 mg PO qid for 10 days
• Alternative regimen (2): Metronidazole 500–750 mg PO three times daily for 10 days
• Alternative regimen (3): Paromomycin 25–35 mg/kg/day PO in three divided doses for 7 days

• 1.1 Treatment in pregnancy

• Iodoquinol use in pregnancy is limited, and risk to the embryo-fetus is unknown, should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
• Metronidazole is in pregnancy category B. Data on the use of this drug in pregnant women are conflicting. The available evidence suggests use during pregnancy has a low risk of congenital anomalies. May be used during pregnancy in those patients who will clearly benefit from the drug, although its use in the first trimester is generally not advised.
• Oral dose of Paromomycin generally is poorly absorbed from the gastrointestinal tract, with minimal, if any, systemic availability.

• 1.2 Treatment during lactation

• Iodoquinol should be used with caution in breastfeeding women.
• Metronidazole should be used during lactation only if the potential benefit of therapy to the mother justifies the potential risk to the infant.
• Oral dose of Paromomycin is unlikely to be excreted in breast milk, and the drug generally is poorly absorbed from the gastrointestinal tract.

• 1.3 Treatment in pediatric patients

• Iodoquinol 30–40 mg/kg/day (maximum 2 g) PO in 3 doses for 􏰄20 days. The safety of iodoquinol in children has not been established.
• Tetracycline 40 mg/kg/day (maximum 2 g) PO in 4 doses for􏰄 10 days
• Metronidazole 35–50 mg/kg/day PO in 3 doses for􏰄 10 days. The safety in children has not been established, is listed as an antiamebic and antigiardiasis medicine on the WHO Model List of Essential Medicines for Children, intended for the use of children up to 12 years of age.
• Paromomycin 25–35 mg/kg/day PO in 3 doses􏰄 for 7 days. The safety of oral dose in children has not been formally evaluated. However, the safety profiles likely are comparable in children and adults.