Emerging from Obscurity: Biological, Clinical, and Diagnostic Aspects of Dientamoeba fragilis

Abstract

Ever since its first description in 1918, Dientamoeba fragilis has struggled to gain recognition as a significant pathogen. There is little justification for this neglect, however, since there exists a growing body of case reports from numerous countries around the world that have linked this protozoal parasite to clinical manifestations such as diarrhea, abdominal pain, flatulence, and anorexia. A number of studies have even incriminated D. fragilis as a cause of irritable bowel syndrome, allergic colitis, and diarrhea in human immunodeficiency virus patients. Although D. fragilis is most commonly identified using permanently stained fecal smears, recent advances in culturing techniques are simplifying as well as improving the ability of investigators to detect this organism. However, there are limitations in the use of cultures since they cannot be performed on fecal samples that have been fixed. Significant progress has been made in the biological classification of this organism, which originally was described as an ameba. Analyses of small-subunit rRNA gene sequences have clearly demonstrated its close relationship to Histomonas, and it is now known to be a trichomonad. How the organism is transmitted remains a mystery, although there is some evidence that D. fragilis might be transmitted via the ova of the pinworm, Enterobius vermicularis. Also, it remains to be answered whether the two distinct genotypes of D. fragilis recently identified represent organisms with differing virulence

Dientamoeba fragilis: an emerging role in intestinal disease

“…1 Early studies pointed toward the pinworm, Enterobius vermicularis, as a potential vector: coinfection with D. fragilis and E. vermicularis initially appeared to be far more common than expected; amoeboid bodies resembling D. fragilis have been described in the eggs of E. vermicularis; and the parasitologist Ockert (again, in the tradition of self-experimentation) successfully infected himself and 2 other adult volunteers by ingesting E. vermicularis eggs taken from a child coinfected with D. fragilis.…”

“…F irst described in 1918 by Jepps and Dobell, Dientamoeba fragilis is a binucleated, unflagellated protozoan related to the trichomonads, 1 readily identified in stool specimens by means of routine iron-hematoxylin stains. First observed in 7 patients, of whom 6 had diarrhea or dysentery, the parasite was dubiously classified as a nonpathogen based on its source of nutrition: its voracious appetite is for the commensal bacteria of the gut rather than the tissues of its host.…”

“…1,8 This regimen was studied in a small case series of 21 people with IBS-like symptoms and concomitant infection with D. fragilis who were treated with iodoquinol and doxycycline: the symptoms resolved in 14 of the patients (67%), in whom the organism was eradicated. In a more recent study of secnidazole treatment, 9 a single dose eradicated the parasite in 34 of 35 patients (97%, 95% CI 92%-100%) and resolved clinical symptoms in 27 cases (77%, 95% CI 63%-91%).…”

İrrite Bağırsak Sendromunda Dientamoeba fragilis ve Blastocystis spp.'nin Rolü

“…fragilis bilimsel literatürde ilk defa 1907 yılında Wenyon tarafından bulunmuş, daha sonra 1918 yılında Jepps ve Dobell tarafından tanımlanmış amibe benzeyen, sadece trofozoit formu bulunan, insan çekum ve kalın barsağının lümeninde yaşayan bir protozoondur (5). Keşfedileli 90 yıl gibi bir süre olmasına rağmen, bu protozoonla ilgili bilgiler diğer protozoonlarla karşılaştırıldı-ğında çok azdır.…”

“…Avustralya'da yapılan bu çalışmada, İBS şikayeti olan 21 hastada D. fragilis enfeksiyonu varlığı gösterilmiş ve iyodokuinoldoksisiklin tedavisinden sonra D. fragilis eradikasyonu ve hastaların çoğunda klinik iyileşme görüldüğü bildirilmiştir. Dünyada prevalans %1.4 ile %52 arasında değişmektedir (5). Ülkemizde yapılan az sayıda çalışmada ise D. fragilis prevalansı İzmir, Van, Malatya ve Manisa bölgesinde sırasıyla %0,2; %0,4; %0,4 ve %1,02 olarak bildirilmiştir (7)(8)(9)(10).…”