Laboratory Studies

Blood tests

Blood test results are usually normal in patients with Dientamoeba fragilis infection. However, a CBC count with 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 polymerase chain reaction (PCR) techniques.^[10]Culture is not routinely available.

Preferred stool preparation involves a fresh sample that is immediately preserved 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 because 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 use barium because barium interferes with trophozoite detection and may do so for several weeks.

Other medications that can interfere with parasite detection include 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 test findings are usually normal.

Treatment & Management

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Media Gallery

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

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Author

Maria A Garcia Fernandez, MD Physician, Department of Infectious Diseases, St Jude Children’s Research Hospital

Disclosure: Nothing to disclose.

Coauthor(s)

Maria A Carrillo-Marquez, MD Assistant Professor, Department of Pediatrics, Division of Infectious Diseases, Le Bonheur Children's Hospital, University of Tennessee Health Science Center College of Medicine

Maria A Carrillo-Marquez, MD is a member of the following medical societies: American Academy of Pediatrics, Infectious Diseases Society of America, Pediatric Infectious Diseases Society

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.

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

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.

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.