Common problems of parasites identification in stool analysis

1. Common Problems
in Parasite Identification
STOOL
ANALYSIS

2. Common ProblemsSTOOL
ANALYSIS in Parasite Identification ͚
Strongyloides stercoralis
rhabditiform larva
Root hair artifact
that resembles actual nematode larva.
Note the internal structures, especially
the large, genital primordium packet of
cells (circle).

3. (b) Root hair (plant material)
Note There is no specific internal structure
The end is ragged (broken off from the main plant)
Note The short buccal capsule (mouth opening)
The internal structure, including the genital primordial
packet of cells.
• Plant material often mimics some of the human parasites.
• This comparison is one of the best examples.
• These artifacts are occasionally submitted as proficiency-testing
specimens
(a) Strongyloides Stercoralis Rhabditiform Larva
Common ProblemsSTOOL
ANALYSIS in Parasite Identification ͛

4. Pollen grain can resemble an actual Taenia egg
NOTE that the shape may vary, especially depending on
the way the pollen grain is lying in the wet preparation
NOTE
The striated shell
6-hooked embryo (oncosphere) within the shell.
Pollen grain (Right)
Taenia egg (Left)
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ANALYSIS in Parasite Identification 3

5. (a) Entamoeba Histolytica Trophozoite
NOTE The evenly arranged nuclear chromatin
Central compact karyosome
The relatively clean cytoplasm.
(b) Entamoeba coli trophozoite
NOTE The unevenly arranged nuclear chromatin
Eccentric karyosome
Messy cytoplasm
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ANALYSIS in Parasite Identification 4
These characteristics are very representative of the 2 organisms

6. (a) Entamoeba histolytica trophozoite
Note Evenly arranged nuclear chromatin
Central compact karyosome
Clean cytoplasm.
(b) Entamoeba coli trophozoite
Note The nuclear chromatin appears to be evenly arranged
The karyosome appears central
While the cytoplasm is still Messy with numerous
vacuoles and ingested debris
The nuclei of these 2 organisms tend to resemble one another
(a very common finding in routine clinical specimens).
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ANALYSIS in Parasite Identification 5

7. E. histolytica trophozoite
Again, note the typical morphology
• Evenly arranged nuclear chromatin
• Central compact karyosome,
• Relatively clean cytoplasm
These organisms show some characteristics
that are very similar (very common in clinical
specimens).
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ANALYSIS in Parasite Identification 6
E. coli trophozoite
Although the nuclear chromatin is
eccentric, note that the karyosome
seems to be compact and central.
However, note the various vacuoles
containing ingested debris.

8. In patients with diarrhea or dysentery, E. histolytica trophozoites and
macrophages are often confused, occasionally leading to a false-positive
diagnosis of amebiasis when no parasites are present. Both the actual
trophozoite and the macrophage may also be seen without ingested RBCs and
can mimic one another.
Evenly arranged chromatin
Central compact karyosome
RBCs in the cytoplasm.
Human macrophage
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ANALYSIS in Parasite Identification 7
E. histolytica trophozoite
The key difference between the
macrophage nucleus and that of
E. histolytica is the size. Usually
the ratio of Nucleus to Cytoplasm
in a macrophage is 1:6 or 1:8,
while the true organism has a
N/C ratio of 1:10 or 1:12.
The macrophage also contains
ingested RBCs

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ANALYSIS in Parasite Identification 8
(b) Bee Pollen artifact
This artifact certainly mimics the T. trichiura egg.
However, note that the shape is somewhat distorted.
(a) Trichuris Trichiura Egg
This egg is typical and is characterized by
The barrel shape with thick shell and two polar plugs.
This is an excellent example of a parasite look-alike
that could be confusing.

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ANALYSIS in Parasite Identification 9
(a) Taenia Egg
This egg has been described as having a thick, radially
striated shell containing a six-hooked embryo (oncosphere).
(b) Pollen Grain
Note that this trilobed pollen grain has a similar type of “shell”
and, if turned the right way, could resemble a Taenia egg.
This similarity represents another source of confusion between a
helminth egg and a plant material artifact. When examining fecal
specimens in a wet preparation, you can tap on the coverslip to
get objects to move around. As they move, you can see more
morphologic detail.

11. Common ProblemsSTOOL
ANALYSIS in Parasite Identification 10
Trichuris
Trichiura
Egg
Pollen
that can mimic a T. Trichiura Egg
(Examples of pine pollen)

12. Common ProblemsSTOOL
ANALYSIS in Parasite Identification 11
(d) Yeast cells in fecal material.
Yeast cells in fecal material. Note the shape tends
to be consistent and there appears to be no
particular direction of placement such as is seen
frequently with RBCs.
(a) RBCs on a stained fecal smear.
Note that the cells are very pleomorphic but tend
to be positioned in the direction in which the stool
was spread onto the slide.
(b) Yeast cells on a stained fecal smear.
These cells tend to remain oval and are not aligned
in any particular way on the smear.
(c) PMNs and RBCs (see arrows).
The RBC cell shape can vary tremendously.
These differences are important when the differential
identification is between E. histolytica containing RBCs
and E. coli containing ingested yeast cells. If RBCs or
yeast cells are identified in the cytoplasm of an
organism, they must also be visible in the background of
the stained fecal smear.
a
b
c
d

13. Human cells in permanent stained smears
(Left) Macrophage
Note the large size of the nucleus (the N/C ratio is much
larger than in the amebae in the genus Entamoeba).
(Right) PMN
Note the lobed nucleus; when the lobes break apart, the
“individual nuclei” can mimic those seen in amebae.
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ANALYSIS in Parasite Identification 12

14. (a) Entamoeba histolytica mature cyst
Note that the 4 nuclei are very consistent in size and shape.
(b) Polymorphonuclear leukocyte (PMN)
Note that the normal lobed nucleus has now broken into 4 fragments,
which mimic four nuclei with peripheral chromatin and central
karyosomes. When PMNs have been in the gut for some time and
have begun to disintegrate, the nuclear morphology can mimic that
seen in an E. histolytica cyst.
However, human cells are often seen in the stool in patients with
diarrhea; with rapid passage of GIT contents, there will not be time for
amebic cysts to form. Therefore, for patients with diarrhea and/or
dysentery, if “organisms” that resemble the cell in panel b are seen,
think first of PMNs, not E. histolytica.
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ANALYSIS in Parasite Identification 13

15. (b) Polymorphonuclear leukocyte (PMN)
• The nucleus is somewhat lobed (normal morphology) and represents a
PMN that has not been in the gut very long.
• Occasionally, the positioning of the chromatoidal bars and the lobed
nucleus of the PMN will mimic one another. The chromatoidal bars stain
more intensely, but the shapes can overlap, as seen here.
(a) Entamoeba histolytica precyst
NOTE The enlarged nucleus (prior to division)
with evenly arranged nuclear chromatin
and central compact karyosome
Chromatoidal bars (rounded ends with smooth edges) are
also present in the cytoplasm.
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ANALYSIS in Parasite Identification 14