Nonhuman Elements Seen in Feces (Yeast Cells)
There are many yeast cells that may be round to oval and measure ~4 to 8 µm which can be seen in fecal material. On a wet mount, they may resemble small protozoan cysts (Endolimax nana or Entamoeba hartmanni). After staining, they appear fairly uniform in color (red to green with trichrome stain) without many inclusions; if granules are seen, they are usually small but may resemble small protozoan karyosomes. Depending on the stain used, small yeast cells can be confused with coccidian oocysts or microsporidial spores. It is important to note the presence of budding yeast cells and/or pseudohyphae (clinically relevant only in freshly preserved specimens). The presence of branching pseudohyphae may be an indication of pathogenicity of the particular yeast present (usually Candida spp.) and should be reported. Large numbers of budding yeast cells in a fresh or freshly preserved specimen, indicating a potential source for a systemic infection, particularly in immunosuppressed patients, should also be reported (Fig. 10.22).
Figure 10.22 Yeast cells in clinical specimens. (Upper and middle) Trichrome-stained fecal smears. Depending on the size and permanent stain used (trichrome, modified acid-fast, modified trichrome), single yeast cells can often be confused with the coccidia or microsporidia. (Bottom left) Various yeasts in blood films; (right) Histoplasma within monocytes. doi:10.1128/9781555819002.ch10.f22
Note Because yeast can continue to grow if the stool is not immediately preserved, some laboratories do not report yeast, since the report can be misleading. They elect to call the physician and discuss the findings. Another option is to add a report comment indicating that reports of yeast (budding and/or pseudohyphae) might be misleading due to a lag time between stool passage and specimen fixation.
Finding insect larvae in stool is not common but may occur as a result of ingestion of whole larvae or adult insects with food. The presence of live larvae may suggest myiasis or, probably more common, contamination of the stool specimen. In these situations, it is always important to find out how and when the specimen was collected prior to submission, particularly if it was submitted as a fresh stool. Proper fixation of the suspected object is important for further identification (see chapter 9).
Spurious infections occur when individuals ingest liver from various animals. The various parasite eggs are digested free when the liver is eaten and will be passed in the stool for several days. Repeat ova and parasite examinations are recommended for several days to rule out a true infection. Examples are eggs of Fasciola hepatica, Dicrocoelium dendriticum, or Capillaria hepatica, which are present in the livers of cattle, sheep, and rodents, respectively (12). Occasionally, rarer eggs are found and may represent spurious infections acquired by eating the flesh of fish, birds, or other animals, both vertebrates and invertebrates (Fig. 10.23). In a true human infection with Capillaria hepatica, no eggs are found in the stool as they are in an infection with Capillaria philippinensis; diagnosis requires histologic examination. Eggs in liver biopsy specimens can be identified on the basis of their characteristic morphology.
Figure 10.23 (Top row, left) Fasciola hepatica egg (130 to 150 µm by 63 to 90 µm) (image is lower magnification than Dicrocoelium egg); (right) Dicrocoelium dendriticum egg (38 to 45 µm by 22 to 30 µm). (Middle row, left) Capillaria philippinensis egg (51 to 68 µm by 30 to 35 µm), passed in the stool (resembles egg of Trichuris trichiura); (right) Capillaria hepatica eggs in liver. (Bottom row, left) Capillaria philippinensis egg; (right) Trichuris trichiura egg. Note the striated shell of C. philippinensis compared with the nonstriated shell seen in the Trichuris egg. doi:10.1128/9781555819002.ch10.f23
Delusory Parasitosis (Delusional Infestation)
Occasionally, clinical specimens in which the patient has placed various objects or organisms to feign parasitism are submitted for examination. These patients are usually mentally disturbed and have often seen numerous physicians and submitted clinical specimens to many laboratories. The objects placed in the specimens range from pieces of thread to plant material to earthworms. Often, these patients call the laboratory with extensive histories of “parasitic infections” and seek referrals to other experts or consultants. They may bring photographs or samples of the “parasites” that they have found, all of which will be submitted for identification. These “infections” are not limited to specimens such as stool but may include skin, urine, and other samples for analysis. Often, these patients are women older than 50 years, with possible other medical problems, who present with a wide variety of symptoms. It is likely that dopaminergic and serotonergic dysfunction may play a role in delusional parasitosis; dopamine and serotonin antagonists may be relevant for the treatment of this disorder (13–16).
This disease can become a tremendous burden both for the patient and for the family. Patients can appear to be very rational about everything else, with the exception of their beliefs concerning infection or infestation with parasites. However, actual infections have been misdiagnosed as delusory parasitosis when appropriate diagnostic procedures have not been used and the true infections have been missed. A thorough investigation for parasites on the patient, on pets, and in the work and home environment should be completed before assigning a diagnosis of delusory parasitosis.
Patients with delusory parasitosis pose a difficult interdisciplinary problem for the medical system. Such patients avoid psychiatrists and consult dermatologists, microbiologists, or general practitioners but often lose faith in professional medicine. Epidemiology and history suggest that the imaginary pathogens may continually change, while the delusional aspect remains constant. Patients with self-diagnosed “Morgellons disease” can be seen as a variation of this delusional theme (15). Reference 15 provides very comprehensive information on all aspects of this disorder, including recommendations for physician/patient interactions and guidance algorithms.
The minimal criteria for delusional infestation are as follows:
• A strong conviction of being infested by pathogens (small, vivid, inanimate [rare], often “new to science”) without any medical or microbiological evidence for this, ranging from overvalued ideas to a fixed, unshakable belief.
• Report of abnormal sensations in the skin explained by the first criterion.
Additional symptoms may include visual illusions or hallucinations. Although the “infestation” is generally associated with the skin, all parts of the body may be involved. Often this condition has gone on for months or years (15).
References
1. Belding DL. 1965. Textbook of Parasitology, 3rd ed. Appleton-Century-Crofts, New York, NY.
2. Patterson DJ.
