Case7 Supervisor: Dr. 盧章智 Reporter: I2 郭俸志

Case  A 5-year-old girl had been suffering from intermittent diarrhea, nausea, general malaise, and unexplained loss of appetite and had complained of a stomach ache.  The child was in nursery school and had recently been diagnosed with a pinworm infection. She had been treated for this infection and seemed to make a full recovery. Her pediatrician ordered laboratory tests, including a complete blood count, a stool culture, and three stool specimens for examination for ova and parasites.

Case 7  Slight eosinophilia was reported.  The stool culture was negative for enteric bacterial pathogens.  The slides of the concentrated specimens for ova and parasites were negative for all three specimens.  Two of the three permanent smears stained by the trichrome method were reported negative; the third specimen showed a few protozoan trophozoites (Fig. 7.1). P.S.: Trichrome stain:alternative to iron hematoxylin for staining protozoa. Protozoa have bluish-green to purple cytoplasms with red or purplish-red nuclei and inclusion bodies; specimen back ground is green

Case 7  Each trophozoite measured 7 to 14 um, and appeared slightly rounded. Although two nuclei were present in most trophozoites seen, some of the cells had only a single nucleus.  A delicate nuclear membrane was only slightly visible. The nuclear chromatin was fragmented into four or five chromatin granules located symmetrically. Peripheral nuclear chromatin was absent. Vacuoles containing bacteria were present in the cytoplasm.

Fig. 7.1

Question 1  Which intestinal protozoan parasite fits the description given? What is the nature of the confusion surrounding the classification of this parasite?

Answer 1  Dientamoeba fragilis  Classification of intestinal and urogenital protozoa -amoebae -flagellates (Giardian lamblia, Dientamoeba fragilis, and Trichomonas vaginalis) -ciliate -coccidian -microsporidian parasites

Question 2  What may be the association of pinworm infection with this patient's present infection?

Answer 2  The pinworm and Dientamoeba fragilis both spread by fecal-oral transmission.

Question 3  In addition to this parasite, which other parasitic infections are common in nursery schools?

Answer 3  fecal-oral transmission cycle -Giardia lambliaGiardia lamblia -Entamoeba histolyticaEntamoeba histolytica -Balantidium coli

Question 4  Would you expect to find cysts as well as trophozoites in the stool specimen?

Answer 4  Only trophozoite forms of Dientamoeba fragilis are detected in fecal specimens from infected patients

Life cycle of Dientamoeba fragilis

 The complete life cycle of this parasite has not yet been determined, but assumptions were made based on clinical data. To date, the cyst stage has not been identified in D. fragilis life cycle, and the trophozoite is the only stage found in stools of infected individuals. D. fragilis is probably transmitted by fecal-oral route and transmission via helminth eggs (e.g., Ascaris, Enterobius spp.) has been postulated. Trophozoites of D. fragilis have characteristically one or two nuclei (, ), and it is found in children complaining of intestinal (e.g., intermittent diarrhea, abdominal pain) and other symptoms (e.g., nausea, anorexia, fatigue, malaise, poor weight gain).

Clinical Features:  Symptoms that have been associated with infection include diarrhea, abdominal pain, anorexia, nausea, vomiting, fatigue, and weight loss.

Laboratory Diagnosis:  Infection is diagnosed through detection of trophozoites in permanently stained fecal smears (e.g., trichrome). This parasite is not detectable by stool concentration methods. Dientamoeba fragilis trophozoites can be easily overlooked because they are pale- staining and their nuclei may resemble those of Endolimax nana or Entamoeba hartmanni.

Treatment:  Safe and effective drugs are available. The drug of choice is iodoquinol. Paromomycin*, tetracycline*, (contraindicated in children under age 8, pregnant and lactating women) or metronidazole can also be used