Dientamoeba Fragilis Infection

Updated: Oct 02, 2023
  • Author: Maria A Garcia Fernandez, MD; Chief Editor: Russell W Steele, MD  more...
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Overview

Practice Essentials

Dientamoeba fragilis is a nonflagellate trichomonad parasite 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. [1]  D fragilis has been detected in untreated sewage. [2]

The mode of transmission is not well understood, and conflicting evidence has been published. [3]  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. [4]  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).

Educate patients and caregivers about the importance of effective handwashing techniques.

Signs and symptoms

Abdominal pain and diarrhea are the most common symptoms in patients with D fragilis infection.

See Presentation for more detail.

Diagnosis

Blood test results are usually normal in patients with D fragilis infection. However, a complete blood cell (CBC) count with differential may reveal eosinophilia in up to 50% of children infected with the parasite.

The usual method for confirming the diagnosis is examination of a permanently stained smear of fresh feces, preserved immediately, for the morphologic characteristics of D fragilis trophozoites. Newer methods include immunofluorescence and real-time polymerase chain reaction (PCR) techniques.

See Workup for more detail.

Management

The goal of therapy is eradication of the parasite D fragilis. The drugs used are considered investigational by the US Food and Drug Administration because of a lack of clinical trials.

See Treatment and Medication for more detail.

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Pathophysiology

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.

Etiology

The mode of transmission is believed to be through direct fecal-oral spread and, possibly, through the eggs of E vermicularis (pinworm). Pigs have been identified as a natural host for D fragilis, [4] raising the possibility of transmission from porcine waste, and the parasite has also been identified in untreated wastewater. [2]

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Epidemiology

International statistics

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.

A prospective study from Spain that included 44 D fragilis patients and their 97 household contacts reported that 50.5% of household contacts had a positive PCR for D fragilis. The study also reported that patients with children were more associated with coinfection. [5]

A study conducted in Italy by Calderaro et al found an overall prevalence of 3.7% for D fragilis infection, as well as an increasing trend in prevalence from 2.8% in 2011-2015 to 4.8% in 2016-2020. The researchers suggest that the more frequent use of diagnostic molecular techniques may have contributed to the rise in prevalence. [6]

A retrospective study in Finland reported that Dientamoeba was the most commonly detected pathogenic enteroparasite. [7]

Age-related demographics

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.

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Prognosis

Morbidity/mortality

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. [8]

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.

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