Plasmodium malariae: Morphology

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Morphology of Plasmodium malariae
*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).

(See Malaria Biology pages for an explanation of these stages)

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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.

• Generally large rings forms, red cells not usually multiply infected
• Red cells begin to enlarge and may have ovoid or fimbriated apearance
• James' dots (morphologically indistinguishable from Schüffner's dots) begin to appear
• Pigment will not generally be detected at the early trophozoite stage

GALLERY

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The late trophozoite

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As parasites grow but generally retain their general ring shape, maturation is accompanied by clear modification of red cells to become ovoid and/or fimbriated; metabolism of haemoglobin causes malaria pigment to form.

• Parasites become larger and thickened, although the ring form is generally retained
• Red cell enlargement may lead to the ovoid fimbriated form often described as "comet forms"
• James' dots will now be prominent in appropriately stained specimens
• Pigment will now be seen over the surface of the parasite

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).

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Geographical distribution

P. malariae infection overlaps that of P.falciparum including sub-Saharan Africa, isoutheast Asia, in Indonesia, the western Pacific and in areas of the Amazon Basin of South America.

Detailed geographical information may be accessed here: Malaria Atlas Project.

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File:PMET.jpg

The early trophozoite

• Small but well-formed rings are typical, a central chromatin dot may occur; in some cases the parasites may appear elongated
• Red cells are generally of normal size, though occasionally may have reduced volume
• Pigment will not generally be present at this developmental stage

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Late trophozoites

• 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 should not be seen
• Pigment can now be seen over the parasite surface

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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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