Plasmodium falciparum: Morphology

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Plasmodium falciparum

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.

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The early trophozoite

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The earliest growth stage, this is characterised by fine ring forms with few other changes to red cell or parasite.

• Ring forms are fine and delicate and may be the sole form present (synchronicity)
• Frequently the red cells contain multiple parasites
• Parasites may have a distinctive "double dot" or signet ring form
• Parasites may appear on the accolé forms that appear flattened against the cell membrane
• Affected red cells have normal size and haemoglobin content

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The late trophozoite

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The later growth stage of trophozoites where parasites modification of the erythrocyte is seen with characteristic added dots and possible minor changes to red cell form:

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

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The schizont

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The schizont is the asexual form of the malaria parasite that will circulate in blood in most species, but is an uncommon feature in P.falciparum:

• Do not generally circulate in this species consider causes
• The merozoites cluster "untidily" but may be numerous (8-16+ when mature)
• In this species the loose pigment may be seen in clumps between the parasites
• Red cell size is generally unaffected but red cells become pale as haemoglobin is metabolised by the parasites

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The gametocyte

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The sexual replication in P.falciparum is very distinctive and may be the only form visible (particularly of after treatment).

• male and femaie gametocytes have the appearance of rods although these may be distorted
• The rod shapes may become curved by the red cell membrane to give the characteristic "banana" form”
• The residual membrane (empty of haemoglobin) is often seen as a "blister" to one or both sides of the parasite
• The single chromatin area is in the centre of the parasite, often has pigment overlying it

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