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Overview :
The appearance of malaria parasites in the peripheral blood
smear can be used to identify the infecting species.
Steps:
(1) make sure
malaria is present, excluding other parasites (such as Babesia species) and
artifacts (especially platelets or stain debris; platelets are especially a
problem for the inexperienced)
(2) try to
identify all of the forms and features present after an extensive examination
(3) consider the
possibility of a mixed infection with more than one species
Technical issues:
• The proper pH of
the Giemsa stain is very important, especially to show stippling.
• A thick smear
should be used to exclude low level parasitemia but may not be adequate for
speciation.
• A thin smear
should be used to speciate.
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Features in Blood
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P. falciparum
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P. vivax
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P. malariae
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P. ovale
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affected RBC
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normal size
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enlarged, a few ovalocytes
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normal size
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normal to increased; ovalocytosis
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forms in peripheral blood
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ring trophozoites and gametocytes only
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all forms
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all forms
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all forms
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immature trophozoites (ring forms)
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2 chromatin dots; 2+ rings per RBC; applique forms; rings
delicate
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rarely may have 2 chromatin dots or multiple rings per RBC
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mature trophozoites
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not seen
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ameboid
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band or bayonet forms
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schizonts
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not seen
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12-24 merozoites in mature schizonts
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6-12 merozoites in mature schizont, may form a circle
("daisy")
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8-12 merozoites in mature schizont
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gametocytes
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banana shaped
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stippling
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Mauer's dots or clefts (occasional)
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Schuffner's dots (usual)
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Ziemann's dots (rare; if overstain)
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James's stippling
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where:
• applique forms =
ring trophozoites at the edge of the erythrocyte, up against the red cell membrane,
seen in P. falciparum
• stippling may or
may not be present; best seen with Giemsa stain at pH 7.0 to 7.2
Plasmodium falciparum:
• features if
present: banana-shaped gametocytes, 2+ rings per RBC, 2 chromatin dots,
applique ring forms
• features suggesting
mixed with another species (not pure): all forms present, enlarged RBCs
affected, band/bayonet trophozoites, daisy schizont, ameboid trophozoites
Plasmodium malariae:
• features if
present: all forms present, band/bayonet trophozoites, daisy schizont, <= 12
schizonts (may have 6 or 7)
• features
suggesting mixed with another species (not pure): enlarged RBCs affected,
banana gametocytes, > 14 schizonts, 2+ ring forms per RBC, 2 chromatin dots,
applique ring forms
Plasmodium ovale:
• features if present:
ovalocytosis, all forms present, 8-12 schizonts
• features
suggesting mixed with another species (not pure): 6 schizonts, > 14
schizonts, banana gametocytes, band/bayonet trophozoites, ameboid trophozoites,
daisy schizonts, 2+ ring trophozoites per RBC, 2 chromatin dots per ring,
applique ring forms
Plasmodium vivax:
• features if
present: ameboid trophozoites, all forms present, >= 14 schizonts; may
rarely show 2+ rings per RBC or 2 chromatin dots
• features
suggesting mixed with another species (not pure): normal RBCs infected, banana
gametocytes, band/bayonet trophozoites, daisy schizont, < 12 schizonts,
applique ring forms
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