The ring-form trophozoites of Plasmodium ovale usually contain a single chromatin dot, but may sometimes contain double-chromatin dots. Multiple infected RBCs may be seen, which makes the rings difficult to differentiate from P. falciparum. Additionally, the rings may be difficult to differentiate from P. vivax, as the cytoplasm is usually thick with a large chromatin dot. As the trophozoites mature, they are less amoeboid than P. vivax and may exhibit fimbriation (spiking) and Schüffner’s dots. Infected RBCs are not usually enlarged as in P. vivax infections.
The schizonts of P. ovale can be similar to P. vivax, although they tend to be smaller and contain fewer merozoites (4-16, on average 8). Elongation to an oval shape and fimbriation are common. Schüffner’s dots can be observed with proper staining. Pigment is lighter and less coarse, similar to P. vivax.
Images courtesy of the CDC.
