A Wright-stained blood smear shows a parasite identified as Babesia species. Which choice lists the correct organism?

• A. Babesia sp.
• B. Plasmodium malariae
• C. Plasmodium falciparum
• D. Plasmodium vivax

Answer: (A)

Recognizing intraerythrocytic parasites on a Wright-stained smear is about matching the visible features inside red blood cells to the correct organism. Babesia species live inside red cells and are transmitted by Ixodes ticks. On a Wright or Giemsa stain, they often appear as small ring forms within RBCs and may show a Maltese cross arrangement (a tetrad of merozoites) in some cases. They lack the hemozoin pigment that malaria parasites produce, which helps distinguish them from Plasmodium spp.

Because the smear is identified as Babesia species, the best listing is Babesia sp. The malaria parasites listed would display different morphologies: for example, Plasmodium falciparum can have multiple tiny rings in a single RBC and other distinctive forms, Plasmodium vivax and Plasmodium ovale typically enlarge RBCs with Schuffner’s stippling, and Plasmodium malariae shows a rosette pattern of merozoites in schizonts.