The ring-form trophozoites of Plasmodium vivax usually have a thick cytoplasm with a single, large chromatin dot. The rings may be difficult to distinguish from those of P. ovale. The cytoplasm becomes amoeboid and Schüffner’s dots (punctuate red granulation in erythrocytes containing oval bodies) may appear as the trophozoites mature. Infected RBCs are often larger than uninfected RBCs.
The developing schizonts of P. vivax are large and amoeboid. The chromatin is arranged in two or more masses. The pigment is also usually arranged in more than one mass. Mature schizonts contain 12-24 merozoites, each of which contains a dot of chromatin and a mass of cytoplasm.
Images courtesy of the CDC.
