AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

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 with the trophozoite stage. Organisms move most actively in fresh feces, but they 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. The mode of transmission is believed to be through direct fecal-oral spread and possibly through coinfection of eggs of Enterobius vermicularis (ie, pinworm).

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 usually are 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.

Frequency

International

Estimated prevalence in the general population in the United States and in other developed countries is most commonly 2-4%. However, much higher prevalence rates (19-69%) have been reported in specific populations, such as individuals living in crowded conditions (eg, institutions, communal living), living in conditions with poor hygiene, and traveling to developing countries.

Mortality/Morbidity

• Colonization may occur without development of disease. In adults, asymptomatic colonization is present in 75-85% of individuals affected by the parasite. In children, the opposite is true; disease develops in as many as 90% of those colonized.
• No specific mortality is associated with this enteropathogen. Morbidity related to acute infection is in the first 1-2 weeks of the disease, with symptomatology predominated by diarrhea. Chronic infection occurs after 1-2 months of illness and is manifested by abdominal pain.

Age

• 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.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

• Abdominal pain and diarrhea
• • The most common complaints, abdominal pain and diarrhea commonly are associated with each other following infection with D fragilis.
  • In acute infection, duration of symptoms is 1-2 weeks.
    • Diarrhea predominates in acute infection.
    • Diarrheal history may be variable, with either consistently frequent stools (1-4 stools per d) or episodic occurrence of diarrhea.
    • Stools are greenish brown, and their consistency varies from watery to sticky.
    • Occasionally, mucus is noted in the stools, but hematochezia is unusual.
• In chronic infection, duration of symptoms is greater than 1-2 months.
  • Abdominal pain is the more common complaint.
  • In children, pain is variable with regards to location, duration, and character.
• Other GI complaints
• • Anorexia
  • Weight loss
  • Nausea
  • Vomiting
  • Bloating
  • Flatulence
  • Alternating constipation and diarrhea
• Nonintestinal complaints
• • Headache
  • Fever
  • Malaise
  • Fatigue
  • Irritability
  • Weakness
  • Pruritus
  • Urticaria

Physical

• No specific findings are present on physical examination.
• General abdominal tenderness may be noted in some children.

Causes

• The mode of transmission is believed to be through direct fecal-oral spread and, possibly in the eggs of E vermicularis (pinworm).

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Allergic gastroenteritis
Eosinophilic gastroenteritis
Celiac disease

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Blood tests
• • Blood tests are usually normal.
  • However, a complete blood count with a differential may reveal eosinophilia in as many as 50% of children infected with the parasite.
• Stool evaluation
• • 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, but experimental, techniques include immunofluorescence and real-time PCR techniques. Culture is not routinely available.
  • Preferred stool preparation involves a fresh sample that is preserved immediately with polyvinyl alcohol fixative, sodium acetate-acetic acid-formalin fixative, or Schaudinn fixative.
  • Immediate preservation is necessary because in unpreserved feces, the morphologic characteristics of the trophozoites do not persist, and they round up and become granular within 15 minutes at room temperature.
  • A single sample is diagnostic only 50-60% of the time.
  • Three separate samples increase the yield to 70-85%, and 6 separate samples increase the yield to 90-95%.
  • Ensure that stool samples are collected on alternate days since D fragilis can be excreted in a cyclic pattern similar to G lamblia.
  • The final portion of the stool evacuation may contain the most concentrated numbers of trophozoites.
  • Collect stool specimens before radiologic procedures that employ barium because barium interferes with trophozoite detection and may do so for several weeks.
  • Other medications that can interfere with parasite detection are antibiotics, antiprotozoan medication, antimalarials, mineral oil, bismuth-containing preparations, and nonabsorbable diarrheal medications.
  • Process stool specimens in the laboratory with the formalin-ether sedimentation concentration technique and stain with either iron hematoxylin, trichrome, or celestin B.
• Diagnostic characteristics
• • Diagnostic characteristics are a pleomorphic trophozoite ranging in diameter from 5-15 mm (range, 4-30 mm) that contains 1-4 nuclei.
  • The most common form is binucleated. However, approximately 20-30% are uninucleated. Multinucleated forms also can be present.
  • The nuclei are distinctive, with several (4-8) chromatin granules clumped in the center of each nucleus.
  • The cytoplasm frequently contains numerous food vacuoles.

Imaging Studies

• Radiologic tests are usually normal.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

The goal of therapy is eradication of the parasite (see Medication).

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

The goal of therapy is eradication of the parasite. The drugs used are considered investigational by the Food and Drug Administration because of a lack of clinical trials. Response rates for a single course of therapy are 70-90% in the limited data published.

Drug Category: Anthelmintics

Parasite biochemical pathways are different from the human host; thus, toxicity is directed to the parasite, egg, or larvae. Mechanism of action varies within the drug class. Antiparasitic actions may include the following:

1. Inhibition of microtubules, causing irreversible block of glucose uptake
2. Tubulin polymerization inhibition
3. Depolarizing neuromuscular blockade
4. Cholinesterase inhibition
5. Increased cell membrane permeability, resulting in intracellular calcium loss
6. Vacuolization of the schistosome tegument
7. Increased cell membrane permeability to chloride ions via chloride channels alteration

Drug Name	Tetracycline (Sumycin)
Description	Inhibits bacterial protein synthesis by binding with 30S and, possibly, 50S ribosomal subunits.
Adult Dose	500 mg PO qid for 10 d
Pediatric Dose	40 mg/kg/d PO divided qid for 10 d; not to exceed 2 g/d
Contraindications	Documented hypersensitivity; severe hepatic dysfunction
Interactions	Bioavailability decreases with antacids containing aluminum, calcium, magnesium, iron, or bismuth subsalicylate; can decrease effects of oral contraceptives, causing breakthrough bleeding and increased risk of pregnancy; can increase hypoprothrombinemic effects of anticoagulants
Pregnancy	D - Unsafe in pregnancy
Precautions	Photosensitivity may occur with prolonged exposure to sunlight or tanning equipment; reduce dose in renal impairment; consider drug serum level determinations in prolonged therapy; use during tooth development (last one half of pregnancy through age 8 y) can cause permanent discoloration of teeth; Fanconilike syndrome may occur with outdated tetracyclines

Drug Name	Iodoquinol (Vytone, Yodoxin)
Description	Amebicide used in treatment of D fragilis.
Adult Dose	650 mg PO tid for 20 d
Pediatric Dose	30-40 mg/kg/d PO divided tid for 20 d; not to exceed 2 g/d
Contraindications	Documented hypersensitivity; hepatic damage
Interactions	None reported
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Avoid long-term use because optic neuritis, optic atrophy, and peripheral neuropathy have been reported; use caution in patients with thyroid disease

Drug Name	Paromomycin (Humatin)
Description	Amebicidal and antibacterial aminoglycoside obtained from strain of Streptomyces rimosus; active in intestinal amebiasis.
Adult Dose	25-35 mg/kg/d PO divided tid for 7 d
Pediatric Dose	Administer as in adults
Contraindications	Documented hypersensitivity; intestinal obstruction
Interactions	Nephrotoxic potential may increase with concurrent administration of other aminoglycosides, penicillins, cephalosporins, amphotericin B, and loop diuretics
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Because of narrow therapeutic index and toxic hazards associated with extended administration, do not use for long-term therapy; caution in renal failure, hypocalcemia, myasthenia gravis, and conditions that depress neuromuscular transmission; adjust dose in renal impairment

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Outpatient Care

• Ova and parasite testing
• • Consider examination of stool specimens 3-4 weeks after therapy to determine if the parasite was eliminated.
  • Examine fecal specimens from all family members (particularly siblings) of the index case for D fragilis and other parasites. In addition, examine for E vermicularis.
  • Take the expense of ova and parasite (O&P) testing into account when considering follow-up and family member testing.
  • A single stool sample for O&P testing costs approximately US$80 in many US laboratories.

Deterrence/Prevention

• Control measures to limit spread of parasites
• • Disinfect surfaces and equipment handled by children infected by the parasite.
  • Disinfect diapering areas.
  • Separate diapering areas from food preparation sites.
  • Educate about handwashing techniques.
  • Improve personal hygiene.
  • Separate symptomatic individuals.

Patient Education

• Educate patient and caregivers about the importance of effective handwashing techniques.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to diagnose is the major potential legal pitfall. This is particularly true in the rare occurrence that failure to thrive ensues.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• Butler WP. Dientamoeba fragilis. An unusual intestinal pathogen. Dig Dis Sci. Sep 1996;41(9):1811-3. [Medline].
• Cuffari C, Oligny L, Seidman EG. Dientamoeba fragilis masquerading as allergic colitis. J Pediatr Gastroenterol Nutr. Jan 1998;26(1):16-20. [Medline].
• Frenkel LM. Dientamoeba fragilis infection. In: Textbook of Pediatric Infectious Diseases. Vol 2. 4th ed. Elsevier Health Sciences;1998:2403-2406.
• Grendon JH, DiGiacomo RF, Frost FJ. Descriptive features of Dientamoeba fragilis infections. J Trop Med Hyg. Oct 1995;98(5):309-15. [Medline].
• Johnson EH, Windsor JJ, Clark CG. Emerging from obscurity: biological, clinical, and diagnostic aspects of Dientamoebafragilis. Clin Microbiol Rev. Jul 2004;17(3):553-70, table of contents. [Medline].
• Keystone JS, Yang J, Grisdale D, et al. Intestinal parasites in metropolitan Toronto day-care centres. Can Med Assoc J. Oct 1 1984;131(7):733-5. [Medline].
• Medical Letter on Drugs and Therapeutics. Drugs for parasitic infections. Med Lett Drugs Ther. Mar 6 1992;34(865):17-26. [Medline].
• Norberg A, Nord CE, Evengard B. Dientamoeba fragilis--a protozoal infection which may cause severe bowel distress. Clin Microbiol Infect. Jan 2003;9(1):65-8. [Medline].
• 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].
• Shein R, Gelb A. Colitis due to Dientamoeba fragilis. Am J Gastroenterol. Oct 1983;78(10):634-6. [Medline].
• Spencer MJ, Garcia LS, Chapin MR. Dientamoeba fragilis. An intestinal pathogen in children?. Am J Dis Child. Apr 1979;133(4):390-3. [Medline].
• Spencer MJ, Millet VE, Garcia LS, et al. Parasitic infections in a pediatric population. Pediatr Infect Dis. Mar-Apr 1983;2(2):110-3. [Medline].
• Stark DJ, Beebe N, Marriott D, et al. Dientamoebiasis: clinical importance and recent advances. Trends Parasitol. Feb 2006;22(2):92-6. [Medline].
• Turner JA. Giardiasis and infections with Dientamoeba fragilis. Pediatr Clin North Am. Aug 1985;32(4):865-80. [Medline].

Article Last Updated: Mar 31, 2006