Volume 13: Artefacts
Co- Authors: M. Arcari
1, A. Baxendine 1 and C. E. Bennett2
Intersep Ltd 2.
University of Southampton
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.
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.
Image illustrating red and white blood cells in a slide preparation
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.
2: Image illustrating
trichrome stained Charcot-Leyden crystals in a slide preparation (Image courtesy
of The University of Alberta)
3: Image showing
trichrome stained Macrophage in a slide preparation (Image courtesy of The
University of Alberta). Note similarity to Ameoboid structure.
4: Image illustrating
trichrome stained Leucocyte in a slide preparation (Image courtesy of The
University of Alberta). Note similarity to Ameoboid cyst structure.
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 present in a faecal slide preparation may appear similar to parasitic cysts or cell bodies.
Figure 6: Image illustrating Fat Globules in slide preparation
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 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.
Image illustrating Yeast Cells in slide preparation
Image illustrating Yeast Cells in slide preparation. Note similarity to
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.
9: Image illustrating Vegetable cell in slide
preparation. Note similarity to Paragonimus
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 grains are often misinterpreted as parasite eggs, but can often be discerned through size and the presence or absence of important structural elements.
Image illustrating pollen in slide preparation using a colour filter
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.
16: Image illustrating pollen resembling a Hymenolepis
nana egg. Hooks and polar filaments are not visible.
Courtesy of CDC Division of Parasitic Diseases.
Image illustrating geranium pollen cells in slide preparation
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.
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.
19: Image illustrating peach hair in slide
preparation. Note the similarity to Strongyloides
20: Image illustrating vegetable hairs in slide
Image illustrating Insect eggs in slide preparation
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.