What is the pathognomonic microscopic finding in Babesia infection, and what is the typical vector?

• A. Maltese cross tetrads of merozoites within red blood cells.
• B. RBC inclusions resembling rings.
• C. Maltese cross tetrads of merozoites within red blood cells; vector ticks such as Ixodes scapularis.
• D. Schizonts in hepatocytes

Answer: (C)

Babesia multiplies inside red blood cells, and the hallmark finding on a blood smear is the Maltese cross tetrad—four merozoites arranged in a square inside a single red blood cell. This tetrad pattern is highly characteristic of Babesia and helps distinguish it from malaria, where you typically see ring forms and schizonts but not this four-in-a-square arrangement. The parasite is carried by ticks of the Ixodes genus, with Ixodes scapularis being the common vector in parts of North America. So, seeing Maltese cross tetrads inside red blood cells points to Babesia, and knowing the usual tick vector completes the picture of transmission.