About Medical Parasitology

New Infections

Ova & Parasite (O&P) Exams

CPT Codes

Quizzes, General

Quizzes, Histology

Quizzes, Blood

Review Tests


Information Tables

Organism Index (A-Z)

Back To Home Page ->


***Reminder: Slides are copyrighted and cannot be copied for publication.

A 76-year old man was first seen in the clinic as a part of a routine examination. The stool was examined as an O&P exam with both a sedimentation wet examination and a permanent stained smear. No organisms were seen on the sedimentation concentration smear, but the following images represent what was seen on the permanent stained smear. The original case was seen at the Iowa State Hygienic Laboratory.

These images were examined using the oil immersion objective (100x oil immersion).

(Scroll Down for Answers and Discussions)


The images presented in Diagnostic Quiz #84 are the following:

These images contain Pentatrichomonas hominis trophozoites; measurements are seen above. Although this organism was not seen in the wet mount, additional morphology could be seen from the permanent stained slide examinations. This flagellate is considered nonpathogenic.


The genus name, Pentatrichomonas (Trichomonas), is based on the five anterior flagella and a granular parabasal body. P. hominis has been recovered from all parts of the world, in both warm and temperate climates. It is considered to be nonpathogenic, although it is often recovered from diarrheic stools. There is no known cyst stage. The trophozoites live in the cecal area of the large intestine and feed on bacteria. The organism is not considered to be invasive. The trophozoite measures 5 to 15 μm in length and 7 to 10 μm in width. It has a pyriform shape and has both an axostyle and undulating membrane, which help in the identification. The undulating membrane extends the entire length of the body, in contrast to that seen in Trichomonas vaginalis. Additional images are seen below; note undulating membrane comes all the way down the organism (unlike Trichomonas vaginalis in urinary-genital system which comes only half way down).


Routine stool examinations are normally recommended for the recovery and identification of intestinal protozoa. In freshly passed stool specimens, particularly in unformed stool, the motility may be visible. In a wet preparation, one specifically looks for the flagellar movement from the undulating membrane and the presence of the axostyle. These small flagellates are difficult to stain and may even be missed on a permanent stained smear, especially if the stain is pale. In more formed stools, the trophozoites may round up (not encysted) and may not exhibit the characteristic motility seen in more active forms. When preserved fecal specimens are received in the laboratory, the permanent stained smear is the most sensitive method for finding and identifying P. hominis.


It is important to remember that Trichomonas vaginalis is often diagnosed in urine via the organism motility. Since the finding of T. vaginalis in the urine of children can imply the possibility of a sexual transmission, it is very important to keep in mind the possibility of fecal contamination within a child’s urine due to collection issues. Thus P. hominis (nonpathogen in stool) could accidentally be misdiagnosed as T. vaginalis (pathogen / sexually transmitted flagellate) in urine. ANY DIAGNOSIS OF T. VAGINALIS IN A CHILD’S OR INFANT’S URINE SHOULD ALWAYS BE CONFIRMED; the misdiagnosis of P. hominis as T. vaginalis could be misinterpreted as a possible child abuse case.


Since there is no known cyst stage, transmission probably occurs in the trophic form. If ingested in a protecting substance such as milk, these organisms can apparently survive passage through the stomach and small intestine in patients with achlorhydria. P. hominis cannot be transplanted into the vagina, the natural habitat of T. vaginalis. Based on diagnostic test results, the incidence of this organism is relatively low, but it tends to be recovered more often than Enteromonas hominis or Retortamonas intestinalis. However, without the use of the permanent stained smear, the presence of P. hominis may be missed. The infection is diagnosed more often in warm climates and in children rather than adults. Because of the fecal-oral transmission route, preventive measures should emphasize improved hygienic and sanitary conditions. Although P. hominis is commonly found in dogs, puppies, and cats, there is no documented information related to possible transmission to humans.


Since P. hominisis nonpathogenic, there would be no necessity for treatment. However, if the patient remains symptomatic, it would be important to do additional testing for other possible pathogenic parasites, as well as other causes. In this particular case, the patient's symptoms are probably related to some other cause OR a true parasitic pathogen may be present and has not yet been identified (Example: Dientamoeba fragilis).


    Garcia, L.S. 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.

    Garcia, L.S. 2009. Practical Guide to Diagnostic Parasitology, 2nd Ed., ASM Press, Washington, D.C.


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