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  P. Falciparum P. Vivax P. Ovale P. Malariae P. Knowlesi

size infected RBC normal normal to enlarged
(up to 1 1/2× to 2×)
normal or slightly enlarged
(up to 1 1/4×)
round to oval
sometimes fimbriated
normal or smaller than normal

ring/trophozoite stage
  – ring forms <1/3 of RBC
– multiply-infected RBCs
– classic “head phone” form
– appliqué/accolé forms
– ameboid ring form
– Schüffner’s dots
– multiply-infected RBCs
– compact trophozoites
– coarse Schüffner’s dots
– band-form trophozoites
-“basket-form” trophozoites
– often coarse chromatin dot
– 1/3 to 1/2 of the RBC
– band-form trophozoites
– multiply-infected RBCs
– slightly amoeboid and irregular
– appliqué forms (sometimes)
– fine dark brown pigment

  – seldom seen in PB
– 8 to 24 small merozoites
– dark clumped pigment
– 12 to 24 merozoites
– yellowish-brown coagulated pigment
– 6 to 14 merozoites
– large nuclei
– mass of dark-brown pigment
– 6 to 12 merozoites
– sometimes “rosette” appearance
– coarse, dark-brown pigment
– maximum of 16 merozoites
– pigment in many small granules or clumps of brownish black round mass

  – crescent or sausage shaped
– diffuse, scattered pigment
– enlarged RBC
– scattered pigment
– large nucleus
– macrogametocyt course pigment
– microgametocyt diffuse pigment
– discrete red nucleus
– Schüffner’s dots
– compact, fills RBC
– scattered brown pigment
– compact chromatin
– irregularly distributed pigment grains

P. Knowlesi and P. Falciparum can be hard to differentiate when the infecting parasites are predominantly at the early trophozoite or ring form developmental stage, such as double chromatin dots, multiply-infected erythrocytes and appliqué forms.
P. Knowlesi and P. Malariae can not be differentiated by morphological features from mature trophozoites, schizonts and gametocytes.
– severe malaria and a parasitaemia greater than 5,000/μl blood, together with a history of time spent in the forest and forest fringe areas of Southeast Asia, should strongly implicate a P. Knowlesi rather than a P. Malariae infection.