Artefacts

Introduction and Summary

Cysts and trophozoites must be examined carefully in different fields of view and measurement is often essential.  Objects such as epithelial cells and macrophages are around the same size as amoebic trophozoites: the latter may also move and contain red blood cells.  White blood cells, plant and vegetable cells, fat globules, muscle fibres, pollen grains, yeasts cells and air bubbles may be confused with cysts or eggs.  Air bubbles trapped under adhesive tape often resemble Enterobius eggs.  Plant hairs and fibres are easily confused with larvae; algae such as Psorospermium haeckelii may be found in the faeces of patients who have eaten crayfish.  Earthworms may resemble roundworms.  A variety of non-pathogenic ova, cysts and parasites resemble pathogens in terms of size and morphology and careful examination is essential.  Eggs of Heterodera, a parasitic nematode of root vegetables, may resemble hookworm eggs.  Eggs originating from harmless mites in cereals or flour could be confused with hookworm ova but are usually larger.  We recently encountered 160 micron "Schistosome ova" in the urine of a patient complaining of haematuria: we suspected Schistosoma haematobium but, on closer analysis, the eggs contained unidentified insects. This volume provides examples of artefacts that may be confused for parasitic life stages. Artefacts should be considered on the basis of size, shape, lack of organelles and defining feature, and variable reactivity with common stains.

Red and White Blood Cells

Red blood cells and a variety of white blood cells can be easily mistaken for parasitic cells or cysts when observed with microscopy.

Figure 1: Image illustrating red and white blood cells in a slide preparation

White Blood Cells

Charcot-Leyden crystals are a product of eosinophil breakdown and are, therefore, occasionally found in faeces of patients suffering from parasitic disease. They appear red when stained with in a trichrome faecal preparation.

Figure 2: Image illustrating trichrome stained Charcot-Leyden crystals in a slide preparation (Image courtesy of The University of Alberta)

Figure 3: Image showing trichrome stained Macrophage in a slide preparation (Image courtesy of The University of Alberta). Note similarity to Ameoboid structure.

Figure 4: Image illustrating trichrome stained Leucocyte in a slide preparation (Image courtesy of The University of Alberta). Note similarity to Ameoboid cyst structure.

Figure 5: Image illustrating Red Blood Cells in slide preparation.  RBC’s may appear to have a central body and a rim of cytoplasm or granules which could be mistaken for Blastocystis hominis. (Image Courtesy of the University of Alberta)

Fat Globules

Fat globules present in a faecal slide preparation may appear similar to parasitic cysts or cell bodies.

Figure 6: Image illustrating Fat Globules in slide preparation

Emulsifying agents are a useful tool to eliminate potential confusion involving fat globules. The removal of such particles from slide preparations will undoubtedly reduce cases of misdiagnosis.

Yeast Cells

Yeast may resemble protozoan cysts because they are uniform in colour, have few inclusions and no nucleus. Yeast could also be confused with small protozoans like E. nana or with Cryptosporidium or Cyclospora oocysts in wet preparation. In acid-fast stains, the oocysts of Cryptosporidium and Cyclospora species stain pink to red. Yeasts are not acid fast and stain green.

Figure 7: Image illustrating Yeast Cells in slide preparation

Figure 8: Image illustrating Yeast Cells in slide preparation. Note similarity to parasitic oocysts

Vegetable Cells

Plant cells and associated elements seen in faeces may resemble eggs,cysts or cell bodies. Plant cells are often identified by a more irregular outer membrane.

Figure 9: Image illustrating Vegetable cell in slide preparation. Note similarity to Paragonimus eggs.

Figure 10: Image illustrating Vegetable cell in slide preparation. Note similarity to Dipylidium caninum egg packets

Figure 11: Image illustrating Vegetable cell in slide preparation

Figure 12: Image illustrating a Vegetable Spiral in slide preparation. Such spirals may appear similar to proglottids (Image courtesy of the University of Alberta)

Figure 13: Image illustrating Vegetable Spiral in slide preparation

Pollen

Pollen grains are often misinterpreted as parasite eggs, but can often be discerned through size and the presence or absence of important structural elements.

Figure 14: Image illustrating pollen in slide preparation using a colour filter

Figure 15: Image illustrating pollen in slide preparation that could be mistaken for a Taenia egg.  The shell is thinner, of non-uniform thickness, and no hooks are visible.  Image courtesy of CDC Division of Parasitic Diseases.

Figure 16: Image illustrating pollen resembling a Hymenolepis nana egg.   Hooks and polar filaments are not visible.  Courtesy of CDC Division of Parasitic Diseases.

Figure 17: Image illustrating geranium pollen cells in slide preparation

Figure 18: Image illustrating pollen cells in slide preparation. Similar to Taenia eggs, but distinguished by uneven thickness of the wall and lack of internal contents do not suggest an egg.

Hair

Animal and plant hairs are most often and easily mistaken for parasitic nematode worms. Their size and shape may be comparable in many cases, but a lack of internal definition will identify the artefact when compared to the worm. Although nematodes are non-segmented and externally simple organisms, they will often show unique structural characteristics under close examination.

Figure 19: Image illustrating peach hair in slide preparation. Note the similarity to Strongyloides stercoralis.

Figure 20: Image illustrating vegetable hairs in slide preparation

Insect Eggs

Figure 21: Image illustrating Insect eggs in slide preparation

Plant Parasites

Figure 22: Image illustrating Heterodera spp. in slide preparation. Such arasitic nematodes attack root vegetables such as beetroot, turnips and radishes.  Their eggs are 80-120mm by 25-40 mm and can conceivably be confused with hookworm eggs.

Earthworms