Dientamoeba fragilis Infection
Despite its name, Dientamoeba fragilis is not an ameba but a flagellate. This protozoan parasite produces trophozoites; cysts have not been identified. Infection may be either symptomatic or asymptomatic.
The complete life cycle of Dientamoeba fragilis has not yet been determined, and assumptions were made based on clinical data. Historically, this species was known only from the trophozoite stage in stools of infected individuals. In 2014, cyst and precyst stages were described for the first time in clinical human specimens. These data are still considered preliminary and further testing should be done to validate the existence of this stage in the human host.
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 it 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).
Reference: Stark D, Garcia LS, Barratt JLN, Phillips O, Roberts T, Marriot D, Harkness J, Ellis JT. Description of Dientamoeba fragilis cyst and precystic forms from human samples. Journ Clin Micro. 2014; 52: 2680-2683.
Symptoms that have been associated with infection include diarrhea, abdominal pain, anorexia, nausea, vomiting, fatigue, and weight loss.
Dientamoeba fragilis binucleate trophozoites stained with trichrome
Dientamoeba fragilis uninucleate trophozoites stained with trichrome.
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.
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