- Peter F Weller, MD, MACP
Peter F Weller, MD, MACP
- Editor-in-Chief — Infectious Diseases
- Section Editor — Tropical Medicine
- William Bosworth Castle Professor of Medicine
- Harvard Medical School
- Professor of Immunology and Infectious Diseases
- Harvard T. H. Chan School of Public Health
- Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
- Section Editor — Travel Medicine
- Head of Infectious Diseases Unit
- Monash University, Australia
Dientamoeba fragilis is an anaerobic intestinal protozoan parasite. Historically, this organism was among a group of enteric protozoan parasites beginning with Giardia duodenalis (previously G. lamblia) that were initially believed to be commensals and not capable of causing symptomatic illness. As more information became available and antimicrobial agents were developed with activity against these parasites, it became clear that D. fragilis can cause an active infection, although it does not always result in symptomatic disease. (See "Epidemiology, clinical manifestations, and diagnosis of giardiasis" and "Blastocystis species" and "Nonpathogenic enteric protozoa".)
While the capacity of D. fragilis to cause symptomatic intestinal illness is increasingly recognized, there are a number of uncertainties surrounding D. fragilis [1,2]. How uniformly infection with this parasite causes symptoms is not known: in a Danish study, D. fragilis was detected in a greater proportion of fecal samples from the asymptomatic background population in Denmark than from subjects with symptoms . Moreover, the means by which this parasite is transmitted has not been fully defined. Finally, the diagnostic recognition of this parasite in fecal examinations requires specific processing and expertise; thus, it is possible that many infections with D. fragilis may go undiagnosed.
Ultrastructural, immunologic, and genetic analyses place D. fragilis in the family of protozoan flagellates, which includes Trichomonas [2,4]. Unlike other intestinal protozoan organisms that have both trophozoite and hardy cyst stages, for a long time D. fragilis was recognized to exist only as trophozoites. Trophozoites measure 7 to 12 micrometers in diameter, contain one or two nuclei, lack flagellae, and are minimally motile. However, cyst forms of D. fragilis have been identified in experimental mouse infections and in human fecal samples , suggesting that cystic forms are the transmissible infectious form of this organism.
There is genetic evidence for at least two variants of D. fragilis. However, it is unknown if these two differ in their pathogenicity .
Infections with D. fragilis are acquired by the fecal-oral route, but how fragile trophozoites survive outside of the body and do not succumb to stomach acid following ingestion are not fully understood (figure 1). Some investigators suggested that trophozoites might survive within and be ingested with the eggs of the pinworm Enterobius vermicularis. While this might explain coinfection in some children, it does not likely explain most D. fragilis infections. In addition, some studies have specifically failed to find a correlation between D. fragilis and E. vermicularis infections . The recognition of cyst forms of the parasite may be important for understanding transmission . In addition, sheep, pigs, and nonhuman primates have been identified as natural hosts of the genotypes found in humans, suggesting zoonotic potential for human transmission . (See "Enterobiasis (pinworm) and trichuriasis (whipworm)".)
- Weiss LM, Keohane EM. The uncommon gastrointestinal Protozoa: Microsporidia, Blastocystis, Isospora, Dientamoeba, and Balantidium. Curr Clin Top Infect Dis 1997; 17:147.
- Johnson EH, Windsor JJ, Clark CG. Emerging from obscurity: biological, clinical, and diagnostic aspects of Dientamoeba fragilis. Clin Microbiol Rev 2004; 17:553.
- Krogsgaard LR, Engsbro AL, Stensvold CR, et al. The prevalence of intestinal parasites is not greater among individuals with irritable bowel syndrome: a population-based case-control study. Clin Gastroenterol Hepatol 2015; 13:507.
- Silberman JD, Clark CG, Sogin ML. Dientamoeba fragilis shares a recent common evolutionary history with the trichomonads. Mol Biochem Parasitol 1996; 76:311.
- Stark D, Garcia LS, Barratt JL, et al. Description of Dientamoeba fragilis cyst and precystic forms from human samples. J Clin Microbiol 2014; 52:2680.
- Johnson JA, Clark CG. Cryptic genetic diversity in Dientamoeba fragilis. J Clin Microbiol 2000; 38:4653.
- Stark D, Beebe N, Marriott D, et al. Prospective study of the prevalence, genotyping, and clinical relevance of Dientamoeba fragilis infections in an Australian population. J Clin Microbiol 2005; 43:2718.
- Cacciò SM, Sannella AR, Manuali E, et al. Pigs as natural hosts of Dientamoeba fragilis genotypes found in humans. Emerg Infect Dis 2012; 18:838.
- Kappus KD, Lundgren RG Jr, Juranek DD, et al. Intestinal parasitism in the United States: update on a continuing problem. Am J Trop Med Hyg 1994; 50:705.
- Girginkardeşler N, Coşkun S, Cüneyt Balcioğlu I, et al. Dientamoeba fragilis, a neglected cause of diarrhea, successfully treated with secnidazole. Clin Microbiol Infect 2003; 9:110.
- Grendon JH, Digiacomo RF, Frost FJ. Dientamoeba fragilis detection methods and prevalence: a survey of state public health laboratories. Public Health Rep 1991; 106:322.
- Windsor JJ, Rafay AM, Shenoy AK, Johnson EH. Incidence of Dientamoeba fragilis in faecal samples submitted for routine microbiological analysis. Br J Biomed Sci 1998; 55:172.
- van Gool T, Dankert J. [3 emerging protozoal infections in The Netherlands: Cyclospora, Dientamoeba, and Microspora infections]. Ned Tijdschr Geneeskd 1996; 140:155.
- Oyofo BA, Peruski LF, Ismail TF, et al. Enteropathogens associated with diarrhea among military personnel during Operation Bright Star 96, in Alexandria, Egypt. Mil Med 1997; 162:396.
- McQuay RM. Parasitologic studies in a group of furloughed missionaries. I. Intestinal protozoa. Am J Trop Med Hyg 1967; 16:154.
- Millet VE, Spencer MJ, Chapin MR, et al. Intestinal protozoan infection in a semicommunal group. Am J Trop Med Hyg 1983; 32:54.
- Stark D, Beebe N, Marriott D, et al. Dientamoeba fragilis as a cause of travelers' diarrhea: report of seven cases. J Travel Med 2007; 14:72.
- Stark D, Barratt J, Roberts T, et al. A review of the clinical presentation of dientamoebiasis. Am J Trop Med Hyg 2010; 82:614.
- Chan F, Stewart N, Guan M, et al. Prevalence of Dientamoeba fragilis antibodies in children and recognition of a 39 kDa immunodominant protein antigen of the organism. Eur J Clin Microbiol Infect Dis 1996; 15:950.
- Grendon JH, DiGiacomo RF, Frost FJ. Descriptive features of Dientamoeba fragilis infections. J Trop Med Hyg 1995; 98:309.
- Norberg A, Nord CE, Evengård B. Dientamoeba fragilis--a protozoal infection which may cause severe bowel distress. Clin Microbiol Infect 2003; 9:65.
- Lagacé-Wiens PR, VanCaeseele PG, Koschik C. Dientamoeba fragilis: an emerging role in intestinal disease. CMAJ 2006; 175:468.
- Cuffari C, Oligny L, Seidman EG. Dientamoeba fragilis masquerading as allergic colitis. J Pediatr Gastroenterol Nutr 1998; 26:16.
- Preiss U, Ockert G, Broemme S, Otto A. On the clinical importance of Dientamoeba fragilis infections in childhood. J Hyg Epidemiol Microbiol Immunol 1991; 35:27.
- Yakoob J, Jafri W, Beg MA, et al. Blastocystis hominis and Dientamoeba fragilis in patients fulfilling irritable bowel syndrome criteria. Parasitol Res 2010; 107:679.
- Crotti D, D'Annibale ML, Fonzo G, et al. Dientamoeba fragilis is more prevalent than Giardia duodenalis in children and adults attending a day care centre in Central Italy. Parasite 2005; 12:165.
- Preiss U, Ockert G, Brömme S, Otto A. Dientamoeba fragilis infection, a cause of gastrointestinal symptoms in childhood. Klin Padiatr 1990; 202:120.
- Banik GR, Barratt JL, Marriott D, et al. A case-controlled study of Dientamoeba fragilis infections in children. Parasitology 2011; 138:819.
- de Jong MJ, Korterink JJ, Benninga MA, et al. Dientamoeba fragilis and chronic abdominal pain in children: a case-control study. Arch Dis Child 2014; 99:1109.
- Gray TJ, Kwan YL, Phan T, et al. Dientamoeba fragilis: a family cluster of disease associated with marked peripheral eosinophilia. Clin Infect Dis 2013; 57:845.
- Windsor JJ, Macfarlane L. Irritable bowel syndrome: the need to exclude Dientamoeba fragilis. Am J Trop Med Hyg 2005; 72:501; author reply 501.
- Windsor JJ, Macfarlane L, Hughes-Thapa G, et al. Detection of Dientamoeba fragilis by culture. Br J Biomed Sci 2003; 60:79.
- Stark D, Beebe N, Marriott D, et al. Detection of Dientamoeba fragilis in fresh stool specimens using PCR. Int J Parasitol 2005; 35:57.
- Stark D, Beebe N, Marriott D, et al. Evaluation of three diagnostic methods, including real-time PCR, for detection of Dientamoeba fragilis in stool specimens. J Clin Microbiol 2006; 44:232.
- Stark D, Al-Qassab SE, Barratt JL, et al. Evaluation of multiplex tandem real-time PCR for detection of Cryptosporidium spp., Dientamoeba fragilis, Entamoeba histolytica, and Giardia intestinalis in clinical stool samples. J Clin Microbiol 2011; 49:257.
- Calderaro A, Gorrini C, Montecchini S, et al. Evaluation of a real-time polymerase chain reaction assay for the detection of Dientamoeba fragilis. Diagn Microbiol Infect Dis 2010; 67:239.
- Maas L, Dorigo-Zetsma JW, de Groot CJ, et al. Detection of intestinal protozoa in paediatric patients with gastrointestinal symptoms by multiplex real-time PCR. Clin Microbiol Infect 2014; 20:545.
- Stark D, Roberts T, Ellis JT, et al. Evaluation of the EasyScreen™ enteric parasite detection kit for the detection of Blastocystis spp., Cryptosporidium spp., Dientamoeba fragilis, Entamoeba complex, and Giardia intestinalis from clinical stool samples. Diagn Microbiol Infect Dis 2014; 78:149.
- Hiatt RA, Markell EK, Ng E. How many stool examinations are necessary to detect pathogenic intestinal protozoa? Am J Trop Med Hyg 1995; 53:36.
- Stark DJ, Beebe N, Marriott D, et al. Dientamoebiasis: clinical importance and recent advances. Trends Parasitol 2006; 22:92.
- Drugs for Parasitic Infections, 3rd Ed, The Medical Letter, New Rochelle, NY 2013.
- Nagata N, Marriott D, Harkness J, et al. Current treatment options for Dientamoeba fragilis infections. Int J Parasitol Drugs Drug Resist 2012; 2:204.
- Nagata N, Marriott D, Harkness J, et al. In vitro susceptibility testing of Dientamoeba fragilis. Antimicrob Agents Chemother 2012; 56:487.
- Stark D, Barratt JL, Roberts T, et al. Activity of benzimidazoles against Dientamoeba fragilis (Trichomonadida, Monocercomonadidae) in vitro and correlation of beta-tubulin sequences as an indicator of resistance. Parasite 2014; 21:41.
- Röser D, Simonsen J, Stensvold CR, et al. Metronidazole therapy for treating dientamoebiasis in children is not associated with better clinical outcomes: a randomized, double-blinded and placebo-controlled clinical trial. Clin Infect Dis 2014; 58:1692.
- Vandenberg O, Souayah H, Mouchet F, et al. Treatment of Dientamoeba fragilis infection with paromomycin. Pediatr Infect Dis J 2007; 26:88.
- van Hellemond JJ, Molhoek N, Koelewijn R, et al. Is paromomycin the drug of choice for eradication of Dientamoeba fragilis in adults? Int J Parasitol Drugs Drug Resist 2012; 2:162.
- Kurt O, Girginkardeşler N, Balcioğlu IC, et al. A comparison of metronidazole and single-dose ornidazole for the treatment of dientamoebiasis. Clin Microbiol Infect 2008; 14:601.
- Stark D, Roberts T, Marriott D, et al. Detection and transmission of Dientamoeba fragilis from environmental and household samples. Am J Trop Med Hyg 2012; 86:233.