Dientamoebiasis

name: Dientamoebiasis
creation_date: '2026-02-12T23:17:11Z'
updated_date: '2026-02-17T21:53:14Z'
synonyms:
- Dientamoeba fragilis infection
- D. fragilis infection
category: Infectious Disease
description: >-
  Dientamoebiasis is a parasitic infection of the large intestine caused by the
  protozoan Dientamoeba fragilis. It is commonly reported worldwide in association
  with gastrointestinal symptoms including diarrhea, abdominal pain, and flatulence,
  though its pathogenicity remains debated. Transmission is thought to occur via the
  fecal-oral route, possibly facilitated by helminth eggs such as those of
  Enterobius vermicularis (pinworm). Clinical outcomes range from asymptomatic
  carriage to chronic gastrointestinal illness.
disease_term:
  term:
    id: MONDO:0024608
    label: dientamoebiasis
  preferred_term: Dientamoebiasis
parents:
- Protozoal infection
- Gastrointestinal infection
infectious_agent:
- name: Dientamoeba fragilis
  infectious_agent_term:
    preferred_term: Dientamoeba fragilis
    term:
      id: NCBITaxon:43352
      label: Dientamoeba fragilis
  description: >-
    A trichomonad protozoan parasite that inhabits the human large intestine.
    Despite its name suggesting an amoeboid nature, it is classified as a flagellate
    closely related to Histomonas and Trichomonas. It exists predominantly in a
    trophozoite form. A cyst stage with a double-layered wall has been
    characterized by transmission electron microscopy in experimentally infected
    rodents, but has not been confirmed in human stool. Trophozoites are
    vulnerable to highly acidic conditions, suggesting they cannot survive
    gastric transit without encystment or a protective vehicle.
  evidence:
  - reference: PMID:27170141
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dientamoeba fragilis is a protozoan parasite of the human bowel, commonly
      reported throughout the world in association with gastrointestinal symptoms.
    explanation: >-
      This comprehensive review identifies D. fragilis as a protozoan parasite
      of the human bowel with worldwide distribution.
  - reference: PMID:10795375
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Although originally described as an amoeboid organism, it has been
      reclassified as a flagellate, on the basis of a number of electron microscopic
      and immunological findings. Except for its lack of a flagellum, D. fragilis
      closely resembles Histomonas and Trichomonas.
    explanation: >-
      Confirms the taxonomic reclassification of D. fragilis from amoeba to
      flagellate and its phylogenetic relationship to Histomonas and Trichomonas.
  - reference: PMID:38250789
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These studies of cysts showed a clear cyst wall surrounding an encysted
      parasite. The cyst wall was double layered with an outer fibrillar layer and
      an inner layer enclosing the parasite. Hydrogenosomes, endoplasmic reticulum
      and nuclei were present in the cysts. Pelta-axostyle structures, costa and
      axonemes were identifiable and internal flagellar axonemes were present.
    explanation: >-
      Transmission electron microscopy of D. fragilis cysts obtained from mice
      and rats reveals detailed ultrastructure including a double-layered cyst wall
      and preserved organelles, providing evidence for the cyst life cycle stage.
transmission:
- name: Co-transmission via Enterobius vermicularis eggs
  description: >-
    A co-transmission hypothesis proposes that D. fragilis is carried within the
    eggs of the pinworm Enterobius vermicularis. D. fragilis DNA has been detected
    inside surface-sterilized E. vermicularis eggs from co-infected patients,
    and the higher-than-expected coincidence of D. fragilis and pinworm infections
    supports this mechanism. Because trophozoites are vulnerable to gastric acid
    and a human cyst stage has not been demonstrated, helminth egg vectoring
    provides a plausible route for surviving transit through the upper GI tract.
  evidence:
  - reference: PMID:23893951
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we detected D. fragilis DNA in 18 (85%) of 21 samples of E. vermicularis
      eggs collected from patients harbouring D. fragilis in faeces. This finding
      supports the hypothesis that E. vermicularis may have an important role in
      the transmission of D. fragilis.
    explanation: >-
      Detection of D. fragilis DNA within the majority of E. vermicularis eggs
      from co-infected patients supports the pinworm co-transmission hypothesis.
  - reference: PMID:10795375
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a resistant cyst stage has not been demonstrated and it is unlikely that
      its trophozoites can survive successfully outside the human host. As a
      consequence of its higher than anticipated coincidence of infection with
      Enterobius vermicularis, transmission may occur via ova of this pinworm.
    explanation: >-
      Notes that the lack of a demonstrated cyst stage makes pinworm
      co-transmission a plausible explanation for D. fragilis spread.
  - reference: PMID:38250789
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We provide evidence that trophozoites of D. fragilis are vulnerable to
      highly acidic conditions.
    explanation: >-
      Demonstrates that trophozoites cannot withstand gastric pH, supporting
      the need for a protective vehicle such as helminth eggs for successful
      oral transmission.
- name: Direct fecal-oral transmission via cysts
  description: >-
    Direct person-to-person fecal-oral transmission has been proposed as an
    alternative to the pinworm co-transmission hypothesis. The identification
    of a cyst stage of D. fragilis in rodents infected with a human isolate
    implies a life cycle similar to most other intestinal protistan parasites,
    where environmentally resistant cysts are shed in feces and ingested by a
    new host. The cyst wall may protect the organism during gastric transit,
    though this stage has not yet been confirmed in human infections.
  notes: >-
    As of 2024, cysts of D. fragilis have been identified only in
    experimentally infected mice and rats. No cyst stage has been confirmed
    in human stool samples. This limits the evidence for direct fecal-oral
    transmission in humans, though it remains a plausible mechanism given
    the ultrastructural characterization of a resistant cyst wall in rodent
    models.
  evidence:
  - reference: PMID:24492020
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Detection of D. fragilis DNA inside Enterobius vermicularis eggs agrees
      with the prediction of Dobell in 1940 that the eggs of a nematode act as a
      vector for transmission. However, the identification of a cyst stage of D.
      fragilis in the stool of rodents infected with a human isolate has also been
      reported, and this implies a life cycle similar to those of most other
      intestinal protistan parasites.
    explanation: >-
      Discusses the cyst stage identified in rodent models as an alternative
      transmission mechanism to helminth egg vectoring.
  - reference: PMID:38250789
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These studies of cysts showed a clear cyst wall surrounding an encysted
      parasite. The cyst wall was double layered with an outer fibrillar layer and
      an inner layer enclosing the parasite.
    explanation: >-
      Characterization of a double-layered cyst wall in rodent-derived cysts
      supports the existence of an environmentally resistant stage that could
      facilitate direct fecal-oral transmission.
  - reference: PMID:21349214
    supports: NO_EVIDENCE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dientamoeba fragilis is an inhabitant of the human bowel and is associated
      with gastrointestinal illness. Despite its discovery over a century ago, the
      details of Dientamoeba's life cycle are unclear and its mode of transmission
      is unknown.
    explanation: >-
      Reviews the unresolved nature of D. fragilis transmission, including the
      possibility of direct fecal-oral spread.
pathophysiology:
- name: Trophozoite colonization of colonic mucosa
  description: >-
    Dientamoeba fragilis trophozoites establish residence in the lumen and on
    the mucosal surface of the large intestine. The organism lacks a well-established
    cyst stage in humans, so trophozoites represent the primary parasitic form
    in the colon. Colonization may be facilitated by ingestion of contaminated
    pinworm eggs harboring viable D. fragilis organisms.
  cell_types:
  - preferred_term: Epithelial cell of large intestine
    term:
      id: CL:0002253
      label: epithelial cell of large intestine
  locations:
  - preferred_term: Large intestine
    term:
      id: UBERON:0000059
      label: large intestine
  evidence:
  - reference: PMID:27170141
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dientamoeba fragilis is a protozoan parasite of the human bowel, commonly
      reported throughout the world in association with gastrointestinal symptoms.
    explanation: >-
      Confirms D. fragilis colonizes the human bowel.
  downstream:
  - target: Mucosal inflammatory response
    description: >-
      Trophozoite colonization of the colonic mucosa triggers local host
      inflammatory and immune responses.
- name: Mucosal inflammatory response
  description: >-
    Colonization by D. fragilis trophozoites elicits a host immune response
    involving mucosal inflammation. Although the precise virulence factors are
    poorly characterized, symptomatic infection is associated with colonic
    mucosal irritation. Peripheral eosinophilia has been observed in some
    patients, suggesting a Th2-skewed or allergic-type immune component.
  cell_types:
  - preferred_term: Epithelial cell of large intestine
    term:
      id: CL:0002253
      label: epithelial cell of large intestine
  - preferred_term: Mature eosinophil
    term:
      id: CL:0000041
      label: mature eosinophil
  biological_processes:
  - preferred_term: Inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  - preferred_term: Defense response to protozoan
    modifier: INCREASED
    term:
      id: GO:0042832
      label: defense response to protozoan
  locations:
  - preferred_term: Large intestine
    term:
      id: UBERON:0000059
      label: large intestine
  evidence:
  - reference: PMID:21637013
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Usually, carriage of Dientamoeba is associated with symptoms such as
      abdominal pain and diarrhea. Moreover, antimicrobial therapy followed by
      resolution of symptoms coincides with the eradication of Dientamoeba.
    explanation: >-
      Supports the pathogenic role of D. fragilis by linking carriage to symptoms
      and symptom resolution to eradication after treatment.
  - reference: PMID:23759351
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report a familial cluster of D. fragilis associated with marked
      peripheral eosinophilia and gastrointestinal symptoms. Dientamoeba fragilis
      infection should be considered in the setting of unexplained eosinophilia.
    explanation: >-
      Reports marked eosinophilia in D. fragilis infection, suggesting an
      eosinophilic inflammatory component to the host response.
  - reference: PMID:40153748
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The proportion of individuals with D fragilis and a parasite load less
      than 1 trophozoite per field was higher in asymptomatic individuals (controls)
      than in symptomatic cases (47.7% vs 3.1%, respectively) (P < .001). Parasite
      load is associated with the presence of gastrointestinal symptoms, supporting
      the pathogenicity of D fragilis.
    explanation: >-
      Case-control study demonstrating a dose-dependent relationship between
      parasite load and gastrointestinal symptoms, supporting a pathogenic role
      for D. fragilis mediated through mucosal inflammatory mechanisms.
  - reference: PMID:39052010
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      no significant difference was observed in the frequency of clinical signs
      between the 36 patients who tested positive for Dientamoeba fragilis PCR in
      their stools and the 72 control patients who were PCR negative for this
      protozoan.
    explanation: >-
      Case-control study found no evidence of pathogenicity, with no significant
      clinical differences between D. fragilis carriers and controls, suggesting
      D. fragilis may be a commensal of the digestive tract.
  - reference: PMID:39540993
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No difference in decline in IBS-SS was seen comparing the treatment and
      non-treatment groups at T1 (p = 0.403) or T2 (p = 1.00).
    explanation: >-
      Despite achieving parasitological clearance with treatment, no correlation
      between parasitological cure and clinical symptom improvement was
      established, challenging the causal role of D. fragilis in symptom generation.
  downstream:
  - target: Altered intestinal motility and secretion
    description: >-
      Mucosal inflammation leads to disrupted colonic motility and
      increased secretory activity producing gastrointestinal symptoms.
  - target: Systemic immune activation
    description: >-
      In some patients the inflammatory response extends beyond the gut,
      producing peripheral eosinophilia and cutaneous manifestations.
  notes: >-
    The pathogenicity of D. fragilis remains debated. Some case-control studies
    find no significant difference in clinical signs between D. fragilis-positive
    and -negative patients regardless of parasite load, suggesting it may be a
    commensal of the digestive tract. Others demonstrate a dose-dependent
    association between parasite load and symptoms. Context-dependent factors
    such as co-infections (especially Blastocystis sp.), host immunity, and
    microbiome composition may determine clinical outcomes.
- name: Altered intestinal motility and secretion
  description: >-
    Colonic mucosal inflammation caused by D. fragilis leads to altered
    intestinal motility and increased secretory activity. This manifests
    clinically as diarrhea, abdominal pain, flatulence, and nausea. The
    mechanisms likely involve local release of inflammatory mediators that
    affect smooth muscle contractility and epithelial ion transport.
  biological_processes:
  - preferred_term: Inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  locations:
  - preferred_term: Large intestine
    term:
      id: UBERON:0000059
      label: large intestine
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common clinical symptoms include abdominal pain, persistent
      diarrhoea, loss of appetite, weight loss and flatulence.
    explanation: >-
      Lists the gastrointestinal symptoms resulting from intestinal
      dysfunction in D. fragilis infection.
- name: Systemic immune activation
  description: >-
    In a subset of patients, the immune response to D. fragilis extends
    beyond the intestinal mucosa, resulting in peripheral eosinophilia and
    occasionally cutaneous manifestations such as urticaria and pruritus.
    This may reflect a systemic Th2-type response or IgE-mediated
    hypersensitivity to parasite antigens.
  cell_types:
  - preferred_term: Mature eosinophil
    term:
      id: CL:0000041
      label: mature eosinophil
  biological_processes:
  - preferred_term: Innate immune response
    modifier: DYSREGULATED
    term:
      id: GO:0045087
      label: innate immune response
  evidence:
  - reference: PMID:23759351
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report a familial cluster of D. fragilis associated with marked
      peripheral eosinophilia and gastrointestinal symptoms. Dientamoeba fragilis
      infection should be considered in the setting of unexplained eosinophilia.
    explanation: >-
      Demonstrates systemic immune activation with marked eosinophilia
      extending beyond the intestinal mucosa.
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Occasionally, eosinophilia, urticaria and pruritus have been described.
    explanation: >-
      Documents extra-intestinal manifestations including eosinophilia,
      urticaria, and pruritus consistent with systemic immune activation.
phenotypes:
- name: Abdominal pain
  category: Gastrointestinal
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Abdominal pain
    term:
      id: HP:0002027
      label: Abdominal pain
    located_in:
      preferred_term: Large intestine
      term:
        id: UBERON:0000059
        label: large intestine
  evidence:
  - reference: PMID:33137500
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent symptoms were abdominal pain 28.2%, anal itching 27.1%,
      watery diarrhoea 18.8%, meteorism 16.5% and nausea/lack of appetite 14.1%.
    explanation: >-
      Abdominal pain was the most prevalent symptom among D. fragilis-positive
      patients in this Italian cohort.
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common clinical symptoms include abdominal pain, persistent
      diarrhoea, loss of appetite, weight loss and flatulence.
    explanation: >-
      Review identifies abdominal pain as one of the most common symptoms.
- name: Diarrhea
  category: Gastrointestinal
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  evidence:
  - reference: PMID:29404747
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Data from seven studies of specific populations reported that 22% had D.
      fragilis in stools of which only 23% had diarrhea. Eleven studies of stool
      samples submitted to laboratories reported that 4.3% of individuals had D.
      fragilis of which 54% had diarrhea.
    explanation: >-
      Diarrhea is frequently reported in D. fragilis carriers presenting to
      laboratories, though prevalence varies by study setting. Evidence that
      D. fragilis causes diarrhea is inconclusive.
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common clinical symptoms include abdominal pain, persistent
      diarrhoea, loss of appetite, weight loss and flatulence.
    explanation: >-
      Review identifies persistent diarrhea as one of the most common symptoms
      associated with D. fragilis infection.
- name: Flatulence
  category: Gastrointestinal
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Flatulence
    term:
      id: HP:0033589
      label: Flatulence
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common clinical symptoms include abdominal pain, persistent
      diarrhoea, loss of appetite, weight loss and flatulence.
    explanation: >-
      Flatulence is listed among the most common clinical symptoms.
  - reference: PMID:33137500
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent symptoms were abdominal pain 28.2%, anal itching 27.1%,
      watery diarrhoea 18.8%, meteorism 16.5% and nausea/lack of appetite 14.1%.
    explanation: >-
      Meteorism (abdominal bloating/flatulence) was reported at 16.5% in this cohort.
- name: Nausea
  category: Gastrointestinal
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Nausea
    term:
      id: HP:0002018
      label: Nausea
  evidence:
  - reference: PMID:33137500
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent symptoms were abdominal pain 28.2%, anal itching 27.1%,
      watery diarrhoea 18.8%, meteorism 16.5% and nausea/lack of appetite 14.1%.
    explanation: >-
      Nausea and lack of appetite were reported at 14.1% of D. fragilis-positive patients.
- name: Anorexia
  category: Constitutional
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Anorexia
    term:
      id: HP:0002039
      label: Anorexia
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common clinical symptoms include abdominal pain, persistent
      diarrhoea, loss of appetite, weight loss and flatulence.
    explanation: >-
      Loss of appetite is identified as a common clinical symptom.
- name: Weight loss
  category: Constitutional
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Weight loss
    term:
      id: HP:0001824
      label: Weight loss
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common clinical symptoms include abdominal pain, persistent
      diarrhoea, loss of appetite, weight loss and flatulence.
    explanation: >-
      Weight loss is listed among the common clinical symptoms of D. fragilis infection.
- name: Peripheral eosinophilia
  category: Hematologic
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Eosinophilia
    term:
      id: HP:0001880
      label: Increased total eosinophil count
  evidence:
  - reference: PMID:23759351
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report a familial cluster of D. fragilis associated with marked
      peripheral eosinophilia and gastrointestinal symptoms. Dientamoeba fragilis
      infection should be considered in the setting of unexplained eosinophilia.
    explanation: >-
      Case report of a family cluster showing marked peripheral eosinophilia
      associated with D. fragilis infection.
  - reference: PMID:10795375
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Occasionally, eosinophilia, urticaria and pruritus have been described.
    explanation: >-
      Review notes occasional eosinophilia in D. fragilis infection.
- name: Pruritus
  category: Dermatologic
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Pruritus
    term:
      id: HP:0000989
      label: Pruritus
    located_in:
      preferred_term: Skin of body
      term:
        id: UBERON:0002097
        label: skin of body
  notes: >-
    Anal itching (pruritus ani) has been reported as a surprisingly prevalent
    symptom in some studies, potentially related to co-infection with Enterobius
    vermicularis.
  evidence:
  - reference: PMID:33137500
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most prevalent symptoms were abdominal pain 28.2%, anal itching 27.1%,
      watery diarrhoea 18.8%, meteorism 16.5% and nausea/lack of appetite 14.1%.
    explanation: >-
      Anal itching was the second most prevalent symptom at 27.1%, which was
      described as unexpectedly common.
  - reference: PMID:10795375
    supports: NO_EVIDENCE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Occasionally, eosinophilia, urticaria and pruritus have been described.
    explanation: >-
      Pruritus is noted as an occasional feature of D. fragilis infection.
- name: Urticaria
  category: Dermatologic
  frequency: VERY_RARE
  phenotype_term:
    preferred_term: Urticaria
    term:
      id: HP:0001025
      label: Urticaria
    located_in:
      preferred_term: Skin of body
      term:
        id: UBERON:0002097
        label: skin of body
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Occasionally, eosinophilia, urticaria and pruritus have been described.
    explanation: >-
      Urticaria is reported as an occasional feature of D. fragilis infection.
- name: Fatigue
  category: Constitutional
  frequency: OCCASIONAL
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
  evidence:
  - reference: PMID:8794799
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Primarily characterized by diarrhea and abdominal pain, other symptoms
      such as flatulence, nausea, vomiting, fatigue, malaise, and weight loss
      occur.
    explanation: >-
      Case report listing fatigue among the symptoms of D. fragilis infection.
  - reference: PMID:31050625
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dientamoebiasis is globally distributed and detected in a large number of
      subjects with diarrhea, abdominal discomfort, flatulence, fatigue and loss
      of appetite.
    explanation: >-
      Review identifies fatigue as one of the symptoms associated with
      dientamoebiasis globally.
prevalence:
- population: Global
  percentage: 0.3-82.9
  notes: >-
    Reported prevalence of D. fragilis varies enormously worldwide, from 0.3%
    to 82.9% depending on the population studied and diagnostic methods used.
    The introduction of PCR has substantially increased detection rates.
  evidence:
  - reference: PMID:33137500
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The reported prevalence of D. fragilis varies worldwide in different
      populations between 0.3% and 82.9%, and its role as a pathogen is still
      unclear.
    explanation: >-
      Provides the range of global prevalence estimates.
- population: Israeli pediatric population
  percentage: 32.5
  notes: >-
    In a large cohort study of 36,008 children under 18 who underwent multiplex
    PCR testing, 32.5% were positive for D. fragilis. Despite this high
    prevalence, children positive for D. fragilis did not exhibit higher odds
    for pre- or post-test composite clinical outcomes compared to those with
    negative PCR results, suggesting a low positive predictive value for
    clinically significant disease.
  evidence:
  - reference: PMID:39481610
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of 36,008 eligible children, 32.5% were positive for DF and 7.9% for Bs.
    explanation: >-
      Large-scale pediatric cohort study reporting high prevalence of
      D. fragilis in Israeli children detected by multiplex PCR.
treatments:
- name: Paromomycin therapy
  description: >-
    Paromomycin is an aminoglycoside antibiotic with luminal antiprotozoal activity.
    It has shown high eradication rates for D. fragilis and is recommended as
    first-line therapy in several clinical guidelines due to its narrow spectrum
    of activity and minimal systemic absorption.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: paromomycin
      term:
        id: CHEBI:7934
        label: paromomycin
  evidence:
  - reference: PMID:33137500
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our study showed paromomycin had a high efficacy for treatment of D. fragilis
      infections 100.0% (45/45), while caution must be used when using metronidazole
      53.3% (24/40). We recommend paromomycin for empirical treatment, given its
      great effectiveness in our population.
    explanation: >-
      Paromomycin achieved 100% eradication rate compared to 53.3% for
      metronidazole in this Italian cohort.
  - reference: PMID:32155096
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Paromomycin or clioquinol are antibiotics of choice based on their small
      spectrum of activity, fewer side effects, and better eradication rates than
      metronidazole.
    explanation: >-
      Systematic review recommends paromomycin over metronidazole for D. fragilis
      treatment in children based on better eradication and fewer side effects.
- name: Metronidazole therapy
  description: >-
    Metronidazole is an antiprotozoal agent commonly used for D. fragilis infection.
    However, eradication rates are variable and often suboptimal compared to
    other agents.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: metronidazole
      term:
        id: CHEBI:6909
        label: metronidazole
  evidence:
  - reference: PMID:33137500
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our study showed paromomycin had a high efficacy for treatment of D. fragilis
      infections 100.0% (45/45), while caution must be used when using metronidazole
      53.3% (24/40).
    explanation: >-
      Metronidazole showed a lower eradication rate of 53.3% compared to
      paromomycin at 100%, suggesting suboptimal efficacy.
  - reference: PMID:39540993
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treated patients(n = 64) more often tested PCR negative at T1 (64.1% vs.
      16.4%, p < 0.001) and T2 (67.3% vs. 5.3%, p < 0.001) compared to untreated
      patients.
    explanation: >-
      Prospective study showing metronidazole (and clioquinol) achieve
      parasitological clearance, but without a corresponding improvement in
      clinical symptom scores (IBS-SS).
- name: Iodoquinol therapy
  description: >-
    Iodoquinol is a luminal antiprotozoal agent that has been used for D. fragilis
    infections. It is an alternative to paromomycin and metronidazole.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: iodoquinol
      term:
        id: CHEBI:5950
        label: iodoquinol
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment is recommended in symptomatic cases, and iodoquinol, tetracycline
      and metronidazole have been used successfully.
    explanation: >-
      Iodoquinol is listed as one of the agents used successfully for treatment.
- name: Tetracycline therapy
  description: >-
    Tetracycline has been reported as an effective treatment for D. fragilis
    infection in older literature. However, it is generally not recommended
    for children under 8 years of age due to the risk of dental staining,
    limiting its use in the pediatric population where D. fragilis prevalence
    is highest.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    therapeutic_agent:
    - preferred_term: tetracycline
      term:
        id: CHEBI:27902
        label: tetracycline
  evidence:
  - reference: PMID:10795375
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment is recommended in symptomatic cases, and iodoquinol, tetracycline
      and metronidazole have been used successfully.
    explanation: >-
      Tetracycline is listed among agents used successfully for D. fragilis
      treatment, though it has been largely superseded by paromomycin and
      metronidazole in current practice.
diagnosis:
- name: Stool microscopy with permanent staining
  description: >-
    Microscopic examination of permanently stained stool smears (e.g., trichrome
    or iron-hematoxylin stain) to identify the characteristic binucleate
    trophozoites of D. fragilis. Unstained preparations are insufficient for
    definitive diagnosis.
  evidence:
  - reference: PMID:10795375
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Demonstration of the characteristic nuclear structure of D. fragilis, needed
      for a definitive diagnosis, cannot be achieved in unstained faecal material;
      therefore, permanently stained smears are essential.
    explanation: >-
      Permanently stained smears are required to visualize the diagnostic
      nuclear morphology of D. fragilis trophozoites.
- name: Real-time PCR detection
  description: >-
    Molecular detection of D. fragilis DNA in stool samples using real-time PCR
    is a sensitive and specific diagnostic approach. PCR has increasingly replaced
    microscopy in some clinical settings.
  evidence:
  - reference: PMID:30165915
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The introduction of polymerase chain reaction (PCR) is a versatile and
      sensitive diagnostic technique for the detection of intestinal parasites,
      and in some Western world countries PCR has almost completely replaced
      microscopic diagnostics.
    explanation: >-
      PCR has become the dominant diagnostic method for D. fragilis in some
      Western countries due to its sensitivity.
  - reference: PMID:32155096
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both microscopic and Real Time-PCR methods (or a combination of the two)
      can be used for diagnosis.
    explanation: >-
      Both microscopy and RT-PCR are validated diagnostic approaches.
differential_diagnoses:
- name: Irritable bowel syndrome
  description: >-
    IBS presents with chronic or recurrent abdominal pain, bloating, and altered
    bowel habits, closely overlapping with dientamoebiasis symptoms. D. fragilis
    is known to cause IBS-like symptoms and may be misdiagnosed as IBS when
    stool parasitology is not performed. A meta-analysis found no significant
    association between D. fragilis and IBS (OR 1.13, 95% CI 0.22-5.72),
    suggesting the two are distinct conditions with overlapping presentations.
  disease_term:
    preferred_term: Irritable bowel syndrome
    term:
      id: MONDO:0005052
      label: irritable bowel syndrome
  distinguishing_features:
  - IBS is a diagnosis of exclusion with no identifiable infectious agent
  - IBS typically has a relapsing-remitting course unrelated to antimicrobial
    therapy
  - D. fragilis symptoms resolve with targeted antiprotozoal treatment
  - Stool microscopy or PCR can identify D. fragilis trophozoites
  evidence:
  - reference: PMID:17070814
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dientamoeba fragilis is known to cause IBS-like symptoms and has a propensity
      to cause chronic infections but its diagnosis relies on microscopy of stained
      smears, which many laboratories do not perform, thereby leading to the
      misdiagnosis of dientamoebiasis as IBS.
    explanation: >-
      Demonstrates that D. fragilis can mimic IBS and may be misdiagnosed when
      parasitological testing is not performed.
  - reference: PMID:28668983
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      this association was not observed for D. fragilis infection (OR, 1.13; 95%
      CI, 0.22-5.72).
    explanation: >-
      Meta-analysis found no significant association between D. fragilis and IBS,
      supporting the view that they are distinct conditions with overlapping symptoms.
  - reference: PMID:39540993
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A clear and significant correlation between parasitological cure and decline
      of clinical complaints as reported by the participants could not be
      established.
    explanation: >-
      Prospective study showing that eradicating D. fragilis did not improve
      IBS-severity scores, reinforcing the distinction between dientamoebiasis
      and IBS and suggesting clinical overlap without causal relationship.
  - reference: PMID:39481610
    supports: NO_EVIDENCE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Children positive for DF or Bs did not exhibit higher odds for pre- or
      post-test composite outcomes compared to those with all-negative PCR results,
      except for increased rates of abdominal pain and referrals for anti-TTG
      testing among DF-positive children.
    explanation: >-
      Large pediatric cohort found limited clinical significance of D. fragilis,
      with increased anti-TTG referrals among positive children suggesting
      clinicians may consider celiac disease (and by extension IBS) in the
      differential workup.
- name: Giardiasis
  description: >-
    Giardia intestinalis infection presents with diarrhea, abdominal cramps,
    bloating, and flatulence, symptoms largely indistinguishable from
    dientamoebiasis on clinical grounds alone. Both are protozoal infections
    of the intestinal tract transmitted via the fecal-oral route.
  disease_term:
    preferred_term: Giardiasis
    term:
      id: MONDO:0001103
      label: giardiasis
  distinguishing_features:
  - Giardia primarily affects the small intestine, D. fragilis the large
    intestine
  - Giardia has a well-characterized cyst-trophozoite cycle with environmentally
    resistant cysts
  - Giardia can cause steatorrhea and malabsorption, which are uncommon in
    dientamoebiasis
  - Specific stool antigen tests and PCR can differentiate the two organisms
  evidence:
  - reference: PMID:17070814
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Clinical manifestations of Giardia intestinalis infection also vary from
      asymptomatic carriage to acute and chronic diarrhoea with abdominal pain.
      These IBS-like symptoms can be continuous, intermittent, sporadic or
      recurrent, sometimes lasting years without correct diagnosis.
    explanation: >-
      Demonstrates that Giardia infection presents with symptoms overlapping
      with both IBS and D. fragilis, requiring parasitological differentiation.
- name: Blastocystis infection
  description: >-
    Blastocystis sp. is a common intestinal protozoan frequently co-detected
    with D. fragilis. Both cause nonspecific gastrointestinal symptoms and
    their pathogenic significance is debated. Co-infection is common, and
    distinguishing the causative agent requires species-level identification.
  disease_term:
    preferred_term: Blastocystis infectious disease
    term:
      id: MONDO:0005671
      label: Blastocystis infectious disease
  distinguishing_features:
  - Blastocystis has distinct morphological forms (vacuolar, granular, cyst)
    identifiable on microscopy
  - Blastocystis shows stronger epidemiological association with IBS than D.
    fragilis
  - Co-infection with both organisms is frequent and requires species-level
    identification
  evidence:
  - reference: PMID:28668983
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Individuals with Blastocystis infection were found to have a positive
      association with IBS (OR, 2.19; 95% CI, 1.54-3.13), while this association
      was not observed for D. fragilis infection (OR, 1.13; 95% CI, 0.22-5.72).
    explanation: >-
      Meta-analysis distinguishing the epidemiological profiles of Blastocystis
      and D. fragilis in relation to IBS.
  - reference: PMID:33137500
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      32 patients were co-infected with B. hominis (37.7%) and three with G.
      lamblia (3.5%).
    explanation: >-
      High rate of co-infection with Blastocystis hominis in D. fragilis-positive
      patients highlights the need to differentiate the causative agent.
  - reference: PMID:39052010
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Only the concomitant presence of Blastocystis sp. in stools was
      significantly more frequent in the D. fragilis group (uni- and multivariate
      analysis).
    explanation: >-
      Confirms a significant association between D. fragilis and Blastocystis
      co-infection, reinforcing the importance of distinguishing between these
      two organisms when evaluating gastrointestinal symptoms.
- name: Amoebiasis
  description: >-
    Entamoeba histolytica infection can cause symptoms ranging from mild
    diarrhea to severe dysenteric colitis. Non-dysenteric amoebic colitis
    may closely mimic dientamoebiasis with chronic diarrhea and abdominal
    pain.
  disease_term:
    preferred_term: Amoebiasis due to Entamoeba histolytica
    term:
      id: MONDO:0019028
      label: amoebiasis due to Entamoeba histolytica
  distinguishing_features:
  - E. histolytica can cause invasive disease with bloody dysentery and liver
    abscess
  - Trophozoites of E. histolytica contain ingested red blood cells on
    microscopy
  - D. fragilis trophozoites are characteristically binucleate
  - Specific antigen tests and PCR can distinguish the species
  evidence:
  - reference: PMID:17070814
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      clinical diagnosis of amebiasis is often difficult because symptoms of
      patients with IBS may closely mimic those patients with non-dysenteric
      amoebic colitis.
    explanation: >-
      Demonstrates diagnostic overlap between non-dysenteric amoebiasis
      and other causes of chronic GI symptoms including dientamoebiasis.
- name: Celiac disease
  description: >-
    Celiac disease can present with chronic diarrhea, abdominal pain, bloating,
    and fatigue, overlapping with dientamoebiasis. Clinical guidelines
    recommend excluding celiac disease before attributing symptoms to D. fragilis.
  disease_term:
    preferred_term: Celiac disease
    term:
      id: MONDO:0005130
      label: celiac disease
  distinguishing_features:
  - Celiac disease involves gluten-triggered autoimmune enteropathy with villous
    atrophy
  - Serological markers (anti-tTG, anti-EMA antibodies) are absent in
    dientamoebiasis
  - Celiac disease affects the small intestine, not the colon
  - Symptoms in celiac disease respond to gluten-free diet, not antiprotozoal
    therapy
  evidence:
  - reference: PMID:32155096
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment of D. fragilis should be withhold until other causes like celiac
      disease have been excluded.
    explanation: >-
      Clinical guideline recommends excluding celiac disease before attributing
      GI symptoms to D. fragilis and initiating treatment.
clinical_trials:
- name: NCT01314976
  phase: PHASE_IV
  status: COMPLETED
  description: >-
    Randomized, placebo-controlled, double-blinded clinical trial evaluating the
    clinical effect of metronidazole (40 mg/kg/day for 10 days) in D. fragilis-infected
    children with gastrointestinal complaints in Denmark. This was the first controlled
    trial of metronidazole versus placebo for dientamoebiasis.
  target_phenotypes:
  - preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  - preferred_term: Abdominal pain
    term:
      id: HP:0002027
      label: Abdominal pain
  evidence:
  - reference: clinicaltrials:NCT01314976
    supports: SUPPORT
    snippet: >-
      To determine the clinical effect of metronidazole in DF-infected children
      with gastrointestinal complaints, where no other aetiology is known and no
      other gastrointestinal pathogens could be shown.
    explanation: >-
      First placebo-controlled RCT specifically testing metronidazole for
      dientamoebiasis in children, addressing the critical evidence gap around
      treatment efficacy.
  - reference: PMID:24647023
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings do not provide evidence to support routine metronidazole
      treatment of D. fragilis positive children with chronic gastrointestinal
      symptoms.
    explanation: >-
      Published results of this trial (96 participants) showed metronidazole
      did not improve gastrointestinal symptom scores versus placebo despite
      achieving parasitological clearance, with eradication rates declining
      rapidly after treatment cessation.
- name: NCT06907498
  phase: NOT_APPLICABLE
  status: RECRUITING
  description: >-
    Superiority double-blind, randomized controlled trial (COMFORTER Trial)
    comparing paromomycin versus metronidazole for symptomatic D. fragilis
    infection in adults. Primary outcome is clinical improvement or resolution;
    secondary outcomes include microbiological eradication, quality of life, and
    adverse events. Plans to enroll 60 patients (30 per arm).
  target_phenotypes:
  - preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  - preferred_term: Abdominal pain
    term:
      id: HP:0002027
      label: Abdominal pain
  evidence:
  - reference: clinicaltrials:NCT06907498
    supports: SUPPORT
    snippet: >-
      we aim to perform a double blind, randomized controlled trial, evaluating
      the clinical and microbiological efficacy of paromomycin versus metronidazole
      for the treatment of symptomatic adults with PCR positive dientamoeba fragilis.
    explanation: >-
      Head-to-head RCT comparing the two most commonly used treatments for
      D. fragilis, directly relevant to resolving the treatment efficacy debate.
references:
- reference: DOI:10.1007/s12144-021-01700-z
  title: The effect of Blastocystis sp. and Dientamoeba fragilis on
    psychological symptom severity in a sample of clinically diverse males and
    females
  findings: []