Plasmodium knowlesi: Morphology
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Plasmodium knowlesi
Geographical distribution: Rarely seen, since it is acquired only from monkey host in forest or forest-fringe in S.E.Asia with no human to human spread. It is important to recognise this parasite however as travellers from affected areas may contract this species which has rapid division (each 24 hours) and may have high-parasitaemia with the potential for life threatening disease.
The early trophozoite
Early trophozoites will generally be present and broadly resemble P.falciparum
- Ring forms are small and relatively fine (1/3 to 1/2 of erythrocyte diameter)
- Occasional forms are non-vacuolated and double dots may occur at opposite poles
- Multiple parasite infection of cells frequent, but accolé forms rare or absent
- No size change, stippling or pigment at this stage
The late trophozoite
- Usually present and most closely resemble P.malariae
- May be dense amoeboid or band-form, but generally retain a vacuole
- Acquiring pigment at late stages, may be separate or clumped
- Occasional sparse dots may seen (Sinton or Mulligan's stippling)
- Red cell size generally unaffected
The schizont
- Present in mast cases partly resemble P.malariae
- Up to 16 merozoites (exceeds P.malariae)
- Do not generally fill the erythrocyte,.may be irregular or grape-like.
- Erythrocyte not enlarged may be a irregular.
- Dots are often seen.
The gametocyte
- 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
Gallery
Click here to see gallery of Plasmodium malariae forms