Home

About Medical Parasitology

New Infections

Ova & Parasite (O&P) Exams

CPT Codes

Quizzes, General

Quizzes, Histology

Quizzes, Blood

Review Tests

FAQ

Information Tables

Organism Index (A-Z)


Back To Home Page ->
Untitled Document

Presentation of Quiz #23

A 6-year old boy was brought into the clinic after complaining of diarrhea over a two week period. His other symptoms were unremarkable and he had no relevant travel history.

Complete stool examinations were performed (O&P exam: direct wet mount, concentration, and permanent stained slide).

Laboratory results revealed the following:

These images were photographed from permanent stained smears stained with trichrome. Both organisms measure approximately 9 by 12 microns.

Please identify the organisms.

Scroll Down for Answer and Discussion

 

 

 

 

 

 

Answer and Discussion of Quiz #23

The images presented in Diagnostic Quiz #23 are the following:

  1. The image on the left contains an Endolimax nana trophozoite; this trophozoite measured approximately 9 by 12 microns.
  2. The image on the right is a Dientamoeba fragilis trophozoite and also measures approximately 9 by 12 microns. E. nana is considered a non-pathogen, but can mimic the morphology of D. fragilis.

Comment: D. fragilis was first seen in 1909 and described in 1918. On the basis of electron microscopy studies, it has been reclassified as an ameba-flagellate rather than an ameba and is closely related to Histomonas and Trichomonas spp. It has a cosmopolitan distribution, and past surveys provide incidence rates of from 1.4 to 19%. Much higher incidence figures have been reported for mental institution inmates, missionaries, and Indians in Arizona. D. fragilis tends to be common in some pediatric populations, and in some studies, incidence figures are higher for patients under 20 years of age. A cyst form has been confirmed; however, there are rarely more than 1% cysts in any clinical specimen, and they are difficult to identify.

D. fragilis has been associated with a wide range of symptoms. Case reports of children infected with D. fragilis reveal a number of symptoms, including intermittent diarrhea, abdominal pain, nausea, anorexia, malaise, fatigue, poor weight gain, and unexplained eosinophilia. The most common symptoms in patients infected with this parasite appear to be intermittent diarrhea and fatigue. In some patients, both the organism and the symptoms may persist or reappear until appropriate treatment is initiated.

Diagnosis of D. fragilis infections depends on proper collection and processing techniques (a minimum of three fecal specimens). Although survival time for this parasite has been reported as 24 to 48 h, the survival time in terms of morphology is limited, and stool specimens must be examined immediately or preserved in a suitable fixative soon after defecation. It is particularly important that permanently stained smears of stool material be examined with an oil immersion lens (1,000 x). These organisms have been recovered in formed stool; thus, a permanent stained smear must be prepared for every stool submitted for a parasite examination.

If preserved specimens are submitted to the laboratory, it may be more cost effective to begin the stool examination with the concentration procedure rather than the direct wet mount, particularly since motile protozoa will not be viable because of the prior addition of preservative. Even if parasites are seen on a direct mount of preserved stool, they would almost certainly be seen on the concentration examination as well as on the permanent stained smear (protozoa in particular). With few exceptions, intestinal protozoa should never be identified on the basis of a wet mount alone; permanent stained smears should be examined to confirm the specific identification of suspected organisms.

(Consistent with CAP Inspection Checklist): Every stool submitted for an O&P examination must be examined using the concentration and permanent stained smear procedures.

O&P Exam (Fresh Stool Specimen/liquid and/or very soft): Direct wet smear, concentration, permanent stained smear.

O&P Exam (Fresh Stool Specimen/formed stool): Concentration, permanent stained smear.

O&P Exam (Preserved Stool Specimen): Concentration, permanent stained smear.

Remember that all intestinal protozoan infections can be missed if the concentration ONLY is performed. The permanent stained smear is much more sensitive than the concentration alone. To date, there are no commercial immunoassay products available for the confirmation of infection with D. fragilis; however, they are under development

Dientamoeba fragilis, Key Points - Laboratory Diagnosis

  1. Minimum of three specimens (stool) should be submitted for the diagnosis of Dientamoeba infections.
  2. Since the cyst form is quite rare in clinical specimens, D. fragilis will normally not be seen on a wet preparation. Consequently, it is mandatory that a permanent stained smear be included in the ova and parasite examination.
  3. The trophozoite forms have been recovered from formed stool, thus the need to perform the ova and parasite examination on specimens other than liquid or soft stools.
  4. Organisms with a single nucleus can easily be confused with Endolimax nana or Entamoeba hartmanni, both of which are considered nonpathogens.

Life Cycle: The life cycle and mode of transmission for D. fragilis has recently been clarified, although transmission via helminth eggs such as those of Ascaris lumbricoides and Enterobius vermicularis has been postulated. The cyst stage has been confirmed, so transmission is via ingestion of this stage, as well. The trophozoite is characterized as having one (20 to 40%) or two (60 to 80%) nuclei. The nuclear chromatin is usually fragmented into three to five granules, and there is normally no peripheral chromatin on the nuclear membrane. In some organisms, the nuclear chromatin may tend to mimic that of Endolimax nana, Entamoeba hartmanni, or even Chilomastix mesnili, particularly if the organisms are overstained. The cytoplasm is usually vacuolated and may contain ingested debris as well as some large, uniform granules. The cytoplasm can also appear uniform and clean with few inclusions. There can also be considerable size and shape variation among organisms, even on a single smear.

Epidemiology and Control: As reported for many of the intestinal protozoa, D. fragilis is worldwide in distribution. Since fecal-oral transmission has now documented, preventive measures are probably related to hygiene issues. However, since transmission occurs from the ingestion of certain helminth eggs, then the appropriate hygienic and sanitary measures to prevent contamination with fecal material would be appropriate. There is speculation that D. fragilis may be infrequently recovered and identified; low incidence or absence from survey studies may be due to poor laboratory techniques and a general lack of knowledge concerning the organism. In many laboratories this organism is found as often as Giardia.

Most experts agree that the single most effective practice that prevents the spread of infection in the child care setting is good handwashing by the children, staff, and visitors. Rubbing hands together under running water is the most important part of washing away infectious organisms. Premoistened towelettes or wipes and waterless hand cleaners should not be used as a substitute for washing hands with soap and running water. Certainly these guidelines are not limited to infections with D. fragilis, but include all potentially infectious organisms.

Treatment: Clinical improvement has been observed in adults receiving tetracycline; symptomatic relief was reported in children receiving either diiodohydroxyquin, metronidazole, or tetracycline. Current recommendations include iodoquinol, paromomycin or tetracycline. Since symptomatic relief has been observed to follow appropriate therapy, D. fragilis is probably pathogenic in infected individuals who are symptomatic.

The image on the left is a D. fragilis trophozoite; note the clear area within the karyosome. This suggests that the karyosome is about to fragment into several different dots; the image can easily mimic an E. nana trophozoite.

The image in the center is a D. fragilis trophozoite containing two nuclei, both of which have fragmented into several chromatin dots.

The image on the right is an E. nana trophozoite in which the nucleus is very pleomorphic; this organism might be confused with D. fragilis.

References:

  1. Garcia, LS, 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, DC.
  2. Garcia, L.S. 2009. Practical Guide to Diagnostic Parasitology, 2nd Ed., ASM Press, Washington, D.C.

Quizzes

Each Quiz has a two section format: the first section will present the Quiz topic and the second section will provide a discussion of the answer and/or various options in response to the Quiz situation presented to the user. In some situations, there may be more than one correct response.

The content within this site is made possible through the extensive contribution of Lynne S. Garcia, M.S., MT(ASCP), CLS(NCA), BLM(AAB), F(AAM), Director, Consultantation and Training Services (Diagnostic Medical Parasitology and Health Care Administration). For additional information, she can be contacted at LynneGarcia2@verizon.net.

Reference: Garcia, L.S. 2015. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.

Quiz 1 Quiz 2 Quiz 3
Quiz 4 Quiz 5 Quiz 6
Quiz 7 Quiz 8 Quiz 9
Quiz 10 Quiz 11 Quiz 12
Quiz 13 Quiz 14 Quiz 15
Quiz 16 Quiz 17 Quiz 18
Quiz 19 Quiz 20 Quiz 21
Quiz 22 Quiz 23 Quiz 24
Quiz 25 Quiz 26 Quiz 27
Quiz 28 Quiz 29 Quiz 30
Quiz 31 Quiz 32 Quiz 33
Quiz 34 Quiz 35 Quiz 36
Quiz 37 Quiz 38 Quiz 39
Quiz 40 Quiz 41 Quiz 42
Quiz 43 Quiz 44 Quiz 45
Quiz 46 Quiz 47 Quiz 48
Quiz 49 Quiz 50 Quiz 51
Quiz 52 Quiz 53 Quiz 54
Quiz 55 Quiz 56 Quiz 57
Quiz 58 Quiz 59 Quiz 60
Quiz 61 Quiz 62 Quiz 63
Quiz 64 Quiz 65 Quiz 66
Quiz 67 Quiz 68 Quiz 69
Quiz 70 Quiz 71 Quiz 72
Quiz 73 Quiz 74 Quiz 75
Quiz 76 Quiz 77 Quiz 78
Quiz 79 Quiz 80 Quiz 81
Quiz 82 Quiz 83 Quiz 84
Quiz 85 Quiz 86 Quiz 87
Quiz 88 Quiz 89