Plasmodium falciparum: Morphology

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Geographical distribution

P.falciparum infection occurs in tropical and subtropical areas of central and South America, Africa, and S.E.Asia; this resembles the distribution of P.malariae and overlaps but is distinct from the distribution of P.vivax and P.ovale.

Detailed geographical information may be accessed here: [1].

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The early trophozoite

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The earliest developing stage, and often the only form present 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 developing stage:

• Parasites resemble early ring forms, but are thicker and slightly larger
• Additional dots and clefts in cytoplasm when stained correctly (blue and relatively low in number).
• These have a characteristic appearance and are called Maurer's dots and clefts
• Size and shape of infected red cells usually unaffected, but may become crenated
• Look for double chromatin dot, Accolé forms, multiple parasites/cell

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The schizont

File:PFS.jpg

The asexual replication stage:

• 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

File:PFG1.jpg

The sexual replication stage (very distinctive).

• Gametocytes are elongated but are also restricted by the red cell membrane
• They appear as straight rods but frequently curve into a “banana form”
• The residual membrane (empty of haemoglobin) may appear as a "blister" to the side of the parasite
• The single chromatin area is in the centre of the parasite, often pigment overlies or surrounds it
• Gametocytes may not be seen in many cases.

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Gallery

Click here to see gallery of Plasmodium falciparum forms

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