Which feature is characteristic of Plasmodium vivax infection in red blood cells?

• A. Enlarged red blood cells with Schuffner's dots
• B. Small, compact red blood cells without inclusions
• C. RBCs that frequently show Maurer's dots
• D. Infected RBCs always lack hemoglobin pigment

Answer: (A)

Infection with this parasite typically makes red blood cells larger than normal and gives the cells a fine stippling pattern known as Schuffner's dots. The enlarged RBCs (macrocytosis or macro-ovalocytes) reflect how the parasite alters the host cell, and Schuffner's dots are visible in the cytoplasm on stained smears, especially with Giemsa. This combination is characteristic for Plasmodium vivax (and also seen with P. ovale), helping distinguish it from other species. For example, Plasmodium falciparum more often produces normal- or small-sized RBCs and shows Maurer’s dots in the RBC cytoplasm, while the idea that infected cells always lack hemoglobin pigment isn’t correct, since hemozoin pigment can be observed in malaria parasites. Therefore, enlarged RBCs with Schuffner’s dots best reflect P. vivax infection.