Plasmodium malariae: Morphology

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Morphology of Plasmodium malariae
(see Malaria Biology pages for an explanation of these stages)

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Geographical distribution: P. malariae infection overlaps that of P.falciparum in areas that include sub-Saharan Africa, Southeast Asia, Indonesia, the western Pacific and in areas of the Amazon Basin of South America.

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The early trophozoite

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During this later growth stage the rings enlarge and begin to modify the erythrocyte, forming typical features of the species.

• Small but well-formed rings are typically seen someimes with a central chromatin dot or elongation
• Red cells are generally of normal size, though occasionally may have reduced volume
• Pigment will not generally be present at this developmental stage

GALLERY

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The late trophozoite

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• Parasites are larger and may be elongated, sometimes forming a band across the infected red cell
• Red cells remain round, but size is often reduced
• cytoplasmic dots are uncommon but may be seen
• Pigment can now be seen over the parasite surface

GALLERY

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The schizont

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The asexual schizont stage of development will often be identified in the blood of this species, while smaller than P.vivax, species-specific features may not be clearly seen.

• A range of "schizont forms" will generally be present within moderately enlarged red cells
• When mature schizonts may contain 16-24 separate merozoites
• James' dots may be detected in any residual cytoplasm of the erythrocyte
• Pigment will be visible in irregularly distributed clumps

GALLERY

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The gametocyte

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The sexual replication form resembles P.vivax although generally smaller with sme species-specific forms detectable.

• Red cells will generally enlarged and may have ovoid or fimbriated form
• Macrogametocytes (female form) will often entirely fill the erythrocyte
• Microgametocytes (male form) have a cytoplasmic rim with visible James' dots
• Pigment is clumped evenly over the surface of the gametocyte

GALLERY

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• Parasites tend to be small, although less fine than for P.falciparum, the number of parasites in the blood is often low.
• Infected blood tends to include all the developmental stages, some of which have features that particularly define the species
• Red cell are rarely enlarged, and most frequently have reduced size – this is a fairly useful indication of the the presence of P.malariae
• In normally stained samples there will not be added dots or clefts, although in very heavily stained samples these may be detected (name).

Schizonts

• These are often seen in this species – the number of individual merozoites is often low (around 8)
• Mature schizonts may have a characteristic central area of clumped pigment with the merozoites arranged around this forming a “daisy head”
• At this stage the erythrocyte is devoid of haemoglobin and the small size is readily detected

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Gametocytes

• Gametocytes tend to be regular and round in shape.
• The parasites are small and do not generally fill the erythrocyte
• Haemoglobin is absent and pigment overlies the gametocyte

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