Plasmodium falciparum: Blood Stage Parasites

Fig. 1: Normal red cell; Figs. 2-18: Trophozoites (among these, Figs. 2-10 correspond to ring-stage trophozoites); Figs. 19-26: Schizonts (Fig. 26 is a ruptured schizont); Figs.27, 28: Mature macrogametocytes (female); Figs. 29, 30: Mature microgametocytes (male). Illustrations from: Coatney GR, Collins WE, Warren M, Contacos PG. The Primate Malarias. U.S. Department of Health, Education and Welfare, Bethesda, 1971.

Thick Blood Smears

Illustrations from: Wilcox A. Manual for the Microscopical Diagnosis of Malaria in Man. U.S. Department of Health, Education and Welfare, Washington, 1960.

Smears from patients: Plasmodium falciparum rings have delicate cytoplasm and 1 or 2 small chromatin dots. Red blood cells (RBCs) that are infected are not enlarged; multiple infection of RBCs more common in P. falciparum than in other species. Occasional appliqué forms (rings appearing on the periphery of the RBC) can be present.

A B CA, B, C: Multiply infected red blood cells with appliqué forms in thin blood smears.

D ED: Signet ring form.E: Double chromatin dot.

GG: A thick blood smear showing many ring forms of P. falciparum.

Plasmodium falciparum: TrophozoitesSmears from patients:Although rarely seen in peripheral blood smears, older, ring stage parasites are referred to as trophozoites. The cytoplasm of mature trophozoites tends to be thicker and more dense than in younger rings. As P. falciparum trophozoites grow and mature, they tend to retain their ring-like shape and sometimes trace amounts of yellow pigment can be seen within the cytoplasm. Growing trophozoites in P. falciparum can appear slightly amoeboid in shape.

A B

A: Appliqué trophozoite: Note the slight amoeboid appearance of the parasite.B: A larger, more mature trophozoite and smaller, younger ring stage parasites in a thin blood smear.

C D

C, D: More mature and compact trophozoites. Note the presence of pigment in C.

Plasmodium falciparum: SchizontsSmears from patients:Schizonts are seldom seen in peripheral blood. Mature schizonts have 8 to 24 small merozoites; dark pigment, clumped in one mass.

A BA: Immature schizont in thin blood smears.B: Mature schizont.

C DC, D: Ruptured schizonts in a thin blood smear.

Plasmodium falciparum: Gametocytes

Smears from patients: Plasmodium falciparum gametocytes, when mature are crescent or sausage shape. The red blood cell is often distorted or not visible.

A B

C D

A, B, C, D: Gametocytes of P. falciparum in thin blood smears. Note the presence of a “Laveran’s bib," which is not always visible.

EE: Two gametocytes captured from a thick blood smear.