Medscape is available in 5 Language Editions – Choose your Edition here.


Dientamoeba Fragilis Infection

  • Author: David R Mack, MD, FRCPC; Chief Editor: Russell W Steele, MD  more...
Updated: Aug 18, 2015


Dientamoeba fragilis is a nonflagellate trichomonad parasite and is one of the smaller parasites that can live in the human large intestine. Unlike most other intestinal protozoa, its life cycle has no cyst stage; thus, infection between humans occurs during the trophozoite stage. Organisms move most actively in fresh feces but quickly round up when left standing, are sensitive to an aerobic environment, and die and dissociate when placed in saline, tap water, or distilled water. D fragilis has been detected in untreated sewage.[1]

The mode of transmission is not well understood, and conflicting evidence has been published.[2] Surveys of various mammals and birds have only identified nonhuman primates as natural hosts and never in domestic pets; however, recently a high prevalence of infection has been reported in pigs.[3] Thus, there is a possible zoonotic transmission of this parasite, although most infections are believed to be through direct fecal-oral spread and, possibly, through co-infection of eggs of Enterobius vermicularis (ie, pinworm).



Organisms infect mucosal crypts of the large intestine that are located close to the mucosal epithelium, from the cecum to the rectum; however, the cecum and proximal colon are usually affected. This parasite is not known to be invasive and does not cause cellular damage. It may invoke an eosinophilic inflammatory response in the colonic mucosa; thus, symptoms are related to the superficial colonic mucosal irritation. Similar to some other parasites (eg, Cyclospora cayetanensis, Giardia lamblia, Cryptosporidium parvum), the parasite D fragilis has been demonstrated to cause disease in humans regardless of their immune status.

The life cycle of D fragilis is shown in the image below.

This is an illustration of the assumed life cycle This is an illustration of the assumed life cycle of Dientamoeba fragilis, the cause of a protozoan parasitic infection.




Estimated prevalence in the general population in the United States and in other developed countries is most commonly 2-5%. However, much higher prevalence rates (19-69%) have been reported in specific populations, such as individuals living in crowded conditions (eg, institutions, communal living), individuals living in conditions with poor hygiene, and those traveling to developing countries.


Colonization may occur without development of disease, and, in adults, asymptomatic colonization was once thought to be present in 75-85% of individuals infected by the parasite. More recently, it is not believed that asymptomatic carriage is as prevalent as once thought and in children symptomatic disease develops in as many as 90% of those colonized. In 2014, new research was presented at the 24th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) that questioned the pathogenicity of the parasite.[4]

No specific mortality is associated with this enteropathogen. Morbidity related to acute infection occurs in the first 1-2 weeks of the disease, with symptomatology predominated by diarrhea and abdominal pain. Chronic infection occurs after 1-2 months of illness and is manifested by abdominal pain.


Infection may occur at any age. The most common age at which infection has been reported in children is 5-10 years. Interestingly, E vermicularis (pinworm) infection can also occur in the same age group.

Contributor Information and Disclosures

David R Mack, MD, FRCPC Professor, Department of Pediatrics, University of Ottawa Faculty of Medicine; Head, Division of Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Children's Hospital of Eastern Ontario, Canada

David R Mack, MD, FRCPC is a member of the following medical societies: Canadian Paediatric Society, Canadian Association of Gastroenterology, American Gastroenterological Association, North American Society for Pediatric Gastroenterology, Hepatology and Nutrition

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Martin Weisse, MD Program Director, Associate Professor, Department of Pediatrics, West Virginia University

Martin Weisse, MD is a member of the following medical societies: Academic Pediatric Association, American Academy of Pediatrics, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD Clinical Professor, Tulane University School of Medicine; Staff Physician, Ochsner Clinic Foundation

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, Southern Medical Association

Disclosure: Nothing to disclose.

Additional Contributors

Michael D Nissen, MBBS FRACP, FRCPA, Associate Professor in Biomolecular, Biomedical Science & Health, Griffith University; Director of Infectious Diseases and Unit Head of Queensland Paediatric Infectious Laboratory, Sir Albert Sakzewski Viral Research Centre, Royal Children's Hospital

Michael D Nissen, MBBS is a member of the following medical societies: American Academy of Pediatrics, Royal College of Pathologists of Australasia, Royal Australasian College of Physicians, American Society for Microbiology, Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

  1. Stark D, Roberts T, Marriott D, Harkness J, Ellis JT. Detection and transmission of Dientamoeba fragilis from environmental and household samples. Am J Trop Med Hyg. 2012 Feb. 86(2):233-6. [Medline]. [Full Text].

  2. Clark CG, Röser D, Stensvold CR. Transmission of Dientamoeba fragilis: pinworm or cysts?. Trends Parasitol. 2014 Mar. 30(3):136-40. [Medline].

  3. Cacciò SM, Sannella AR, Manuali E, Tosini F, Sensi M, Crotti D, et al. Pigs as natural hosts of Dientamoeba fragilis genotypes found in humans. Emerg Infect Dis. 2012 May. 18(5):838-41. [Medline]. [Full Text].

  4. New Research Questions Pathogenicity of Parasite D fragilis. Medscape. Available at Accessed: 9/9/14.

  5. Stark D, Barratt J, Roberts T, Marriott D, Harkness J, Ellis J. A review of the clinical presentation of dientamoebiasis. Am J Trop Med Hyg. 2010 Apr. 82(4):614-9. [Medline]. [Full Text].

  6. Cuffari C, Oligny L, Seidman EG. Dientamoeba fragilis masquerading as allergic colitis. J Pediatr Gastroenterol Nutr. 1998 Jan. 26(1):16-20. [Medline].

  7. Johnson EH, Windsor JJ, Clark CG. Emerging from obscurity: biological, clinical, and diagnostic aspects of Dientamoeba fragilis. Clin Microbiol Rev. 2004 Jul. 17(3):553-70, table of contents. [Medline].

  8. Verweij JJ, Mulder B, Poell B, van Middelkoop D, Brienen EA, van Lieshout L. Real-time PCR for the detection of Dientamoeba fragilis in fecal samples. Mol Cell Probes. 2007 Oct-Dec. 21(5-6):400-4. [Medline].

  9. Röser D, Simonsen J, Stensvold CR, Olsen KE, Bytzer P, Nielsen HV, 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 Jun. 58(12):1692-9. [Medline].

  10. Röser D, Simonsen J, Nielsen HV, Stensvold CR, Mølbak K. History of antimicrobial use and the risk of Dientamoeba fragilis infection. Eur J Clin Microbiol Infect Dis. 2015 Jun. 34 (6):1145-51. [Medline].

  11. Butler WP. Dientamoeba fragilis. An unusual intestinal pathogen. Dig Dis Sci. 1996 Sep. 41(9):1811-3. [Medline].

  12. Frenkel LM. Dientamoeba fragilis infection. Textbook of Pediatric Infectious Diseases. 4th ed. Elsevier Health Sciences; 1998. Vol 2: 2403-6.

  13. Grendon JH, DiGiacomo RF, Frost FJ. Descriptive features of Dientamoeba fragilis infections. J Trop Med Hyg. 1995 Oct. 98(5):309-15. [Medline].

  14. Keystone JS, Yang J, Grisdale D, et al. Intestinal parasites in metropolitan Toronto day-care centres. Can Med Assoc J. 1984 Oct 1. 131(7):733-5. [Medline].

  15. Kurt O, Girginkardesler N, Balcioglu IC, Ozbilgin A, Ok UZ. A comparison of metronidazole and single-dose ornidazole for the treatment of dientamoebiasis. Clin Microbiol Infect. 2008 Jun. 14(6):601-4. [Medline].

  16. Medical Letter on Drugs and Therapeutics. Drugs for parasitic infections. Med Lett Drugs Ther. 1992 Mar 6. 34(865):17-26. [Medline].

  17. Norberg A, Nord CE, Evengard B. Dientamoeba fragilis--a protozoal infection which may cause severe bowel distress. Clin Microbiol Infect. 2003 Jan. 9(1):65-8. [Medline].

  18. 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(1):27-34. [Medline].

  19. Shein R, Gelb A. Colitis due to Dientamoeba fragilis. Am J Gastroenterol. 1983 Oct. 78(10):634-6. [Medline].

  20. Spencer MJ, Garcia LS, Chapin MR. Dientamoeba fragilis. An intestinal pathogen in children?. Am J Dis Child. 1979 Apr. 133(4):390-3. [Medline].

  21. Stark DJ, Beebe N, Marriott D, et al. Dientamoebiasis: clinical importance and recent advances. Trends Parasitol. 2006 Feb. 22(2):92-6. [Medline].

  22. Vandenberg O, Peek R, Souayah H, Dediste A, Buset M, Scheen R. Clinical and microbiological features of dientamoebiasis in patients suspected of suffering from a parasitic gastrointestinal illness: a comparison of Dientamoeba fragilis and Giardia lamblia infections. Int J Infect Dis. 2006 May. 10(3):255-61. [Medline].

  23. Vandenberg O, Souayah H, Mouchet F, Dediste A, van Gool T. Treatment of Dientamoeba fragilis infection with paromomycin. Pediatr Infect Dis J. 2007 Jan. 26(1):88-90. [Medline].

This is an illustration of the assumed life cycle of Dientamoeba fragilis, the cause of a protozoan parasitic infection.
All material on this website is protected by copyright, Copyright © 1994-2016 by WebMD LLC. This website also contains material copyrighted by 3rd parties.