Plasmodium ovale: Morphology
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Morphology of Plasmodium ovale
(See Malaria Biology pages for an explanation of these stages)
The early trophozoite
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 (indistinguishable from Schuffner’s dots) begin to appear
- Pigment will not generally be detected at the early trophozoite stage
The late trophozoite
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 and distortion causes ovoid fimbriated forms 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
The schizont
The asexual stage of malaria parasite development - only some trophozoites form schizonts, but those that do undergo successive cycles of replication within the red cell to generate multiple "merozoites" that then each invade a new red cell to continue and increase the infection.
- A range of maturing schizonts will generally be present within moderately enlarged red cells
- When mature schizonts may contain 16-24 separate merozoites
- James' dots can be detected in any residual cytoplasm of the erythrocyte
- malaria pigment is visible in irregularly distributed clumps over the schizont surface
The gametocyte
The sexual replication form (very distinctive).
- Red cells are very large and have ovoid or distorted forms
- Macrogametocytes (female form) will often entirely fill the erythrocyte
- Microgametocytes (male form) have a cytoplasmic rim with visible Schüffner's dots
- malaria pigment is clumped evenly over the surface of the gametocyte