Babesia spp. on stained blood films are most similar in appearance to which malaria species?

• A. Plasmodium knowlesi
• B. Plasmodium falciparum
• C. Plasmodium malariae
• D. Plasmodium vivax

Answer: (B)

Babesia parasites in stained blood films look like the early rings of the malaria parasite Plasmodium falciparum. Both can present as tiny, delicate ring forms inside red blood cells, and both may show multiple rings in a single cell. Babesia rings are often very small and can resemble falciparum rings, which is why this species is the closest match. A helpful aid is that Babesia can produce a Maltese cross tetrad inside a red cell in some cases, a feature not seen with Plasmodium falciparum, but in the absence of that finding, the appearance most reminiscent is falciparum’s delicate rings.