There are a number of structures that resemble parasites but are not in fact parasites. These structures, known as artifacts and confusers, are mostly found in stool and blood samples. These stool artifacts and confusers can be caused by disease processes, medications, and/or dietary habits. The presence of free-living organisms in stool as a result of specimen contact with water, sewage, or soil can be perplexing. On blood smears, artifacts and confusers such as stain precipitate, red blood cell abnormalities such as Howell-Jolly bodies, and platelet clumping can be seen.
In addition to the common artifacts and confusers mentioned here, others may be found in parasite study samples. Some of these confounders include free-living amebae, flagellates, ciliates, and nematodes. Ingestion of parasite forms in which humans are not a part of the life cycle may also result in confusers. The following sections provide a brief overview of fourteen of the most common artifacts and confusers.
White Blood Cells
Polymorphonuclear white blood cells (WBCs), which have an average size of 15 m, are frequently confused with amebic cysts, particularly those of Entamoeba histolytica, which have an average size range of 12 to 18 m.
WBCs are commonly found in patients with ulcerative colitis, bacterial dysentery, or intestinal amebiasis. In addition to being amebic cyst-sized, these WBCs have a two-to-four-lobed nucleus that resembles the nucleus of E. histolytica. These WBC lobes appear to be separate nuclei, but they are linked by thin chromatin bands. WBCs lack protozoan nuclear inclusions such as karyosomes and peripheral chromatin.
Careful microscopic focusing is necessary because these bands are often difficult to detect.
Mononuclear WBCs, also known as macrophages or monocytes, can range in size from 28 to 62 m (less on permanently stained preparations) and closely resemble the E. histolytica trophozoite, which can range in size from 8 to 65 m. Red blood cells (RBCs) and debris can be consumed by both structures, but only macrophages consume polymorphonuclear WBCs. The macrophage has one irregularly shaped nucleus that is frequently missing when examined. Although the size range of macrophages overlaps that of E. histolytica, macrophages can be significantly smaller (5 to 10 m). The macrophages may have red-staining round bodies.
Pollen grains with thick walls resemble Taenia spp. eggs but are smaller, measuring 12 to 20 m. Pollen grains can be round or lobed symmetrically. In contrast to Taenia, there are no notable interior structures.
Vegetable cells can be mistaken for helminth eggs. These cells are typically large and roundish oval to irregularly round in shape, with a diameter of up to 150 m. Cell walls are typically thick. The interior of vegetable cells is disorganized and appears to be mostly made up of large vacuoles.
Vegetable spirals have the shape and size of helminth larvae. Vegetable spirals, unlike helminth larvae, do not have a head or tail region. The ladder-like appearance of vegetable spirals distinguishes them from parasitic forms. The ladder is made up of rungs that are closely spaced together.
Charcot-Leyden crystals have the most clinical significance of all the confusers and artifacts discussed in this chapter. They are usually found in stool or sputum samples and are reported when they are found. The presence of these diamond-shaped crystals, which form from eosinophil breakdown products, indicates the occurrence of an unknown immune response. Because such an immune response could be caused by the presence of parasites, it is critical to carefully examine specimens containing Charcot-Leyden crystals.
The round to oval yeast cells range in size from 4 to 8 m and can be confused with protozoan cysts, particularly those of Entamoeba hartmanni (5 to 12 m), Entamoeba nana (4 to 12 m), and Entamoeba hominis (3 to 10 m). Furthermore, there is a strong resemblance between a yeast cell and a Cryptosporidium oocyst (4 to 6 m). Yeast cells, like the other artifacts and confusers, typically lack definite internal structures. However, small granules resembling karyosomes may be seen on occasion. When yeast is in its budding stage, it is easy to distinguish it from parasites.
Plant hair has the size and shape of helminth larvae. Furthermore, plant hair may appear to have an uninteresting internal structure. Further examination reveals that plant hair lacks diagnostic structures such as a buccal cavity, esophagus, intestine, or genital primordium. There is no such thing as a head or tail region.
Plant material may range in diameter from 12 to 150 µm and resemble helminth eggs, particularly an unfertilized Ascaris lumbricoides (38 to 45 µm), in size and shape. This artifact is typically round to oval in shape and may or may not have a definite cell wall. Plant material is often rough in appearance and may have hairs (pseudocilia) extending from its periphery. The interior of the cell looks like a cluster of odd-shaped vacuoles.
Fungal elements may resemble protozoan cysts in size and shape. The absence of interior structures easily differentiates these artifacts from parasitic forms.
In size and shape, epithelial cells frequently resemble amebic trophozoites. Furthermore, epithelial cells have a single nucleus and, like amebic trophozoites, have a distinct cell wall. The typical amebic trophozoite interior structures do not exist in epithelial cells. The cytoplasm of epithelial cells, for example, is usually smooth and free of inclusions. The large epithelial cell nucleus, on the other hand, could be a large chromatin mass resembling a nucleus.
Round to irregular round-shaped starch cells, also known as starch granules, measure less than 10 m and may appear to be protozoan cysts at first glance, especially those of E. hartmanni and E. nana (both measuring 5 to 12 m). Because they lack internal structures, these cells easily differentiate from parasitic forms. A nondescript mass inside the cell that may resemble a nucleus is frequently present. Further examination of this structure reveals the absence of a karyosome or peripheral chromatin. Furthermore, starch cells can be distinguished from parasites by their dark blue black appearance when stained with iodine.
Clumped Or Fused Platelets
Platelets that have clumped or fused appear frequently on Giemsa-stained blood film smears and can be mistaken for malarial parasites, particularly the young trophozoite form. Unlike a malarial parasite, which has a blue cytoplasm and a red chromatin, clumped or fused platelets have varying shades of purple. Furthermore, malarial parasites have a more defined outline than clumped or fused platelets.
On blood smears, Giemsa-stain precipitate may be visible and mistaken for malarial parasites. The color of stain precipitate is usually bluer than that of malarial parasites, and it varies in size and shape.
Red Cell Abnormalities
Giemsa-stained blood smears may show red blood cell abnormalities such as Howell-Jolly bodies or Cabot’s rings. Because of their different staining characteristics, these abnormalities can be easily distinguished from malarial parasites.