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''Dientamoeba fragilis'' is a species of single-celled excavates found in the gastrointestinal tract of some humans, pigs and gorillas. It causes gastrointestinal upset in some people, but not in others. It is an important cause of travellers diarrhoea, chronic diarrhoea, fatigue and, in children,
failure to thrive Failure to thrive (FTT), also known as weight faltering or faltering growth, indicates insufficient weight gain or absence of appropriate physical growth in children. FTT is usually defined in terms of weight, and can be evaluated either by a low ...
. Despite this, its role as a "commensal, pathobiont, or pathogen" is still debated. ''D. fragilis'' is one of the smaller parasites that are able to live in the human intestine. ''Dientamoeba fragilis'' cells are able to survive and move in fresh feces but are sensitive to aerobic environments. They dissociate when in contact or placed in saline, tap water or distilled water.


Etymology

* Di refers to the two nuclei in the trophozoites (feeding stage of the organism). * Ent refers to the enteric environment in which the organism is found. * The species name ''fragilis'' 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. It was first described in 1918.


Dientamoebiasis

There is a continuous debate whether ''D. fragilis'' is considered to be a harmless organism or a pathogenic parasite. Infection with ''D. fragilis'', called
dientamoebiasis Dientamoebiasis is a medical condition caused by infection with ''Dientamoeba fragilis'', a single-cell parasite that infects the lower gastrointestinal tract of humans. It is an important cause of traveler's diarrhea, chronic abdominal pain, chron ...
, is associated variously with symptoms of abdominal pain, diarrhea, weight loss, nausea, fatigue and fever. In one study, ''D. fragilis'' was identified in 0.9% of patients observed. Its coincidence with
enterobiasis Pinworm infection (threadworm infection in the UK), also known as enterobiasis, is a human parasitic disease caused by the pinworm. The most common symptom is itching in the anal area. The period of time from swallowing eggs to the appearance ...
, caused by pinworm (''Enterobius vermicularis''), has been reported. In another study, eosinophilia was present in half of the infected children participating in the case. ''D. fragilis'' does not penetrate the host tissue directly; therefore, some of these symptoms may be caused from irritation which then leads to colonic motility. Infection can occur at any age; however, the most common ages that have been reported are children 5–10 years old.


Diagnosis

In order to diagnose the parasite, patients are required to provide (multiple) fresh stool samples that have been preserved for parasite examination. The multiple samples are required because of parasite detection being difficult, therefore, a sample might be obtained each day to help increase the sensitivity. Patients can also be tested for ''E. vermicularis'' since the two parasites are known to coincide.


Treatment

Once diagnosed, ''E. vermicularis'' is also searched for throughout the body. The age and clinical status of the patient will determine the treatment given. If the patient is a child, a temporary treatment would be offered to test if symptoms can be alleviated, otherwise, another diagnosis and treatment are required. If the child is asymptomatic, then treatment is not necessary.
Iodoquinol The quinoline derivative diiodohydroxyquinoline (INN), or iodoquinol (USAN), can be used in the treatment of amoebiasis. It is poorly absorbed from the gastrointestinal tract and is used as a luminal amebicide. It acts by chelation of ferrous io ...
is the primary drug treatment for dientamoebiasis, unfortunately there are side effects such as abdominal cramping, nausea, and rash. There are other medications that treat dientamoebiasis, including paromomycin and metronidazole. Tetracycline and doxycycline have also been used as a form of treatment. Drugs such as secnidazole and ornidazole have been used as well, but are not available in the United States.


Epidemiology

''Dientamoeba fragilis'' has an estimated prevalence throughout the United States. Unlike majority of parasitic infections, ''D. fragilis'' is more prevalent in well-developed countries as opposed to disadvantaged and resource poor nations. The parasite is also endemic in crowded communities (i.e institutions), populations with unsatisfactory sanitation conditions, and individuals who travel to underprivileged countries. Globally, the prevalence of ''D. fragilis'' ranges from 0.3% to 90%, occurring in multiple countries including many urbanized cities such as Los Angeles, California and Sydney, Australia. Recently, ''D. fragilis'' was considered to be more prevalent than ''Giardia'', thus leading to better diagnostics.


Phylogenetics

''Dientamoeba fragilis'' is a type of
trichomonad Trichomonadida is an order of anaerobic protists, included with the parabasalids. Members of this order are referred to as trichomonads. Some organisms in this order include: *'' Trichomonas vaginalis'', an organism living inside the vagina of ...
. Trichomonads are flagellated organisms but ''D. fragilis'' lacks flagella, having secondarily lost them over evolutionary time. Thus, it is an amoeba of flagellate ancestry. In point of ultrastructural and antigenic view, Dientamoeba is reclassified as a flagellate. The lifecycle of this parasite has not yet been completely determined, but some assumptions have been made based on clinical data. A cyst stage has been reported, although it is yet to be independently confirmed (). If true, ''D. fragilis'' is probably transmitted by the fecal-oral route. Prior to the report of this cyst stage in the lifecycle of ''Dientamoeba'', transmission was postulated to occur by
helminth Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schi ...
eggs (e.g., ''Ascaris'', ''Enterobius'' spp.). The rationale for this suggestion was that ''D. fragilis'' is closely related to the turkey parasite ''Histomonas'', which is known to be transmitted by the eggs of the helminth ''Heterakis''. Since ''D. fragilis'' is known to frequently coinfect with ''E. vermicularis'', this leads to the assumption that ''E. vermicularis'' is a possible vector and mode of transmission. When inside the host, the parasite infects the mucosal crypts of the large intestine. They primarily affect the cecum and proximal colon. It is assumed that when ''D. fragilis'' is inside the colon, it reproduces asexually by binary fission. From there, the trophozoites are in the lumen of the colon, and are excreted as wastes. ''D. fragilis'' is not considered to be invasive nor cause cell or tissue damage.


Build

''D. fragilis'' replicates by binary fission, moves by pseudopodia, and feeds by phagocytosis. The cytoplasm typically contains numerous food
vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
s 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 binucleated form 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. A complex Golgi apparatus is seen; 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.


See also

*
List of parasites (human) Endoparasites Protozoan organisms Helminths (worms) Helminth organisms (also called helminths or intestinal worms) include: Tapeworms Flukes Roundworms Other organisms Ectoparasites References {{Portal bar, Bio ...


References


External links

{{DEFAULTSORT:Dientamoeba Fragilis Metamonads Parasitic excavates Parasites of humans Bacteria described in 1918