Plasmodium falciparum: Morphology

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The early trophozoite

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The earliest growth stage, and may be the only form seen in this species:

• Ring forms that are fine and delicate
• Frequently the red cells contain multiple parasites
• Parasites may have a distinctive double chromatin dot (signet ring form)
• Parasites may appear on the edge of the red cell and have a flattened appearance (accolé forms)
• Affected red cells have normal size and haemoglobin content

Click for P.falciparum early trophozoite gallery

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The late trophozoite

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The later growth stage:

• Parasites resemble early ring forms, but are thicker and may be slightly larger
• Additional blue/grey dots and clefts are seen in cytoplasm when stained correctly
• These added dots have a characteristic appearance Maurer's dots and clefts
• Size and shape of infected red cells is usually unaffected, but red cells may become crenated
• Typical double chromatin dot, accolé forms, and multiple parasites/cell remain present

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The schizont

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• PFS-main image.jpg

The asexual form:

• Do not generally circulate in this species unless overwhelming infection
• Contain multiple asexually formed developing parasites (most frequently 8-16)
• Development is progressive: first there are multiple chromatin dots, later a distinct nucleus and cytoplasm appears
• Loose pigment may be seen in clumps between the parasites
• Red cell size is generally unaffected but haemoglobin will largely be absent (metabolised by the parasites)

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The gametocyte

The gametocyte

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The sexual replication form (very distinctive).

• Gametocytes are elongated but are restricted into typical shape by the red cell membrane
• They parasites are rod shaped but the membrane may cause them to curve into a “"banana" form”
• The residual membrane (empty of haemoglobin) is often seen as a "blister" to the side of the parasite
• The single chromatin area is in the centre of the parasite, often has pigment overlying it
• Gametocytes may not be be seen, or may be the only form present (particularly after treatment)

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