Dientamoebiasis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: : Kalsang Dolma, M.B.B.S.[2]

Dientamoebiasis is a medical condition caused by infection with Dientamoeba fragilis. Dientamoeba fragilis is a single-cell parasite that infects the lower gastrointestinal tract of humans. It is an important cause of travelers diarrhea, chronic abdominal pain, chronic fatigue and failure to thrive in children.

Early microbiologists reported that the organism was not pathogenic, even though six of the seven individuals from whom they isolated it were experiencing symptoms of dysentery. Their report, published in 1918, concluded the organism was not pathogenic because it consumed bacteria in culture, but did not appear to engulf red blood cells as was seen in the most well known disease causing amoeba of the time, Entamoeba histolytica. This initial report may still be contributing to the reluctance of physicians to diagnose the infection.

A study of Dientamoeba fragilis isolates from 60 individuals with symptomatic infection in Sydney Australia found that all were infected with the same genotype.

Although Dientamoeba fragilis has been described as an infection that is “emerging from obscurity,” it has become one of the most prevalent gastrointestinal infections in industrialized countries, especially among children and young adults. A Canadian study reported a prevalence of approximately 10% in boys and girls aged 11-15 years, a prevalence of 11.5% in individuals aged 16-20, and over 20 had a lower incidence of 0.3%-1.9%.

Anyone can become infected with this parasite. However, the risk for infection might be higher for people who have weak immune systems and those who live in or travel to settings with poor sanitary conditions.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: : Kalsang Dolma, M.B.B.S.[2]

Early microbiologists reported that the organism was not pathogenic, even though six of the seven individuals from whom they isolated it were experiencing symptoms of dysentery. Their report, published in 1918, concluded the organism was not pathogenic because it consumed bacteria in culture, but did not appear to engulf red blood cells as was seen in the most well known disease causing amoeba of the time, Entamoeba histolytica. This initial report may still be contributing to the reluctance of physicians to diagnose the infection.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: : Kalsang Dolma, M.B.B.S.[2]

Organisms similar to Dientamoeba fragilis are known to produce a cyst stage that is able to survive outside of the host and facilitate infection of new hosts. However, the exact manner in which Dientamoeba fragilis is transmitted is not yet known, as scientists have reported that the organism is unable to survive outside its human host for more than a few hours after excretion, and no cyst stage has been found.^[1]

Early theories of transmission suggested that Dientamoeba fragilis was unable to produce a cyst stage in infected humans, but some animal existed that in which it did produce a cyst stage, and this animal was responsible for spreading it. However, no such animal has ever been discovered. A later theory suggested the organism was transmitted by pinworms, which provided protection for the parasite outside of the host. Experimental ingestion of pinworm eggs established infection in two investigators. Numerous studies reported high rates of co-infection with helminths [3] However recent study has failed to show any association between Dientamoeba fragilis infection and pinworm infection. Parasites similar to Dientamoeba fragilis are transmitted by consuming water or food contaminated with feces.^[1] The high rate (40%) of concomitant infection with other protazoa reported by at St. Vincent’s Hospital, Sydney, Australia. supports the oral fecal route of transmission.

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  Illustration of the assumed life cycle of Dientamoeba fragilis, the cause of a protozoan parasitic infection. From Public Health Image Library (PHIL). ^[2]

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For patient information click here Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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.

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

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.

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.

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.

• 
  Iron-hematoxylin stained photomicrograph depicts a binucleated amoebic trophozoite of a Dientamoeba fragilis parasite. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph reveals the presence of a trichrome-stained, Dientamoeba fragilis parasitic trophozoites in this specimen. From Public Health Image Library (PHIL). ^[1]
• 
  Photomicrograph reveals the presence of a trichrome-stained, Dientamoeba fragilis parasitic trophozoites in this specimen. From Public Health Image Library (PHIL). ^[1]
• 
  Trichrome-stained photomicrograph reveals the presence of a parasitic Dientamoeba fragilis trophozoite (1150x mag). From Public Health Image Library (PHIL). ^[1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: : Kalsang Dolma, M.B.B.S.[2]

Although Dientamoeba fragilis has been described as an infection that is “emerging from obscurity,” it has become one of the most prevalent gastrointestinal infections in industrialized countries, especially among children and young adults. A Canadian study reported a prevalence of approximately 10% in boys and girls aged 11-15 years, a prevalence of 11.5% in individuals aged 16-20, and over 20 had a lower incidence of 0.3%-1.9%.

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Please help WikiDoc by adding more content here. It’s easy! Click here to learn about editing.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: : Kalsang Dolma, M.B.B.S.[2]

Anyone can become infected with this parasite. However, the risk for infection might be higher for people who have weak immune systems and those who live in or travel to settings with poor sanitary conditions.

Template:Protozoal diseases Template:Gastroenterology

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Please help WikiDoc by adding content here. It’s easy! Click here to learn about editing.

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