Dientamoeba fragilis
Encyclopedia
Dientamoeba fragilis is a single celled parasite found in the gastrointestinal tract of some humans, pigs and gorillas. In some people it causes gastrointestinal upset while in others it does not. It is an important cause of travellers diarhoea, chronic diarhoea, fatigue and in children, failure to thrive.
Etymology of the name Dientamoeba fragilis:
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.
and is associated variously with symptoms of abdominal pain, diarrhea, weight loss, and fever.
In one study, Dientamoeba fragilis was identified in 0.9% of patients observed.
. Trichomonads are flagellated organisms but D. fragilis lacks flagella, having secondarily 'lost' them over evolutionary time. Thus, it is an amoeba of flagellate ancestry.
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.
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 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 hydrogenosome
s, which are also a characteristic of other trichomonads.
Etymology of the name Dientamoeba fragilis:
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
Infection with Dientamoeba fragilis is called DientamoebiasisDientamoebiasis
Dientamoebiasis is a medical condition caused by infection with Dientamoeba fragilis. Dientamoeba fragilis is a single celled parasite that infects the lower gastrointestinal tract of humans...
and is associated variously with symptoms of abdominal pain, diarrhea, weight loss, and fever.
In one study, Dientamoeba fragilis was identified in 0.9% of patients observed.
Phylogenetics
Dientamoeba fragilis is a type of trichomonadTrichomonad
The trichomonads are an order of anaerobic protists, included with the parabasalids. Most are either parasites or other endosymbionts of animals. They typically have four to six flagella at the cell's apical pole, one of which is recurrent - that is, it runs along a surface wave, giving the...
. 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 cycleBiological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
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
Fecal-oral route
The fecal-oral route, or alternatively, the oral-fecal route or orofecal route is a route of transmission of diseases, in which they are passed when pathogens in fecal particles from one host are introduced into the oral cavity of another potential host.There are usually intermediate steps,...
. 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.
Build
Dientamoeba fragilis replicates by binary fission and moves by pseudopodia. D. fragilis feeds by phagocytosis. The cytoplasm typically contains numerous food vacuoleVacuole
A vacuole is a membrane-bound organelle which is present in all 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 molecules including enzymes in solution, though in certain...
s that contain ingested debris, including bacteria. Waste materials are eliminated from the cell through digestive vacuoles by exocytosis
Exocytosis
Exocytosis , also known as 'The peni-cytosis', is the durable process by which a cell directs the contents of secretory vesicles out of the cell membrane...
. 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
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
; 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 hydrogenosome
Hydrogenosome
A hydrogenosome is a membrane-enclosed organelle of some anaerobic ciliates, trichomonads and fungi. The hydrogenosomes of trichomonads produce molecular hydrogen, acetate, carbon dioxide and ATP by the combined actions of pyruvate:ferredoxin oxido-reductase, hydrogenase, acetate:succinate CoA...
s, which are also a characteristic of other trichomonads.
External links
- http://www.dpd.cdc.gov/dpdx/HTML/Dientamoeba.htm
- http://www.emedicine.com/ped/topic563.htm