Which parasite is transmitted by ticks such as Ixodes scapularis and is associated with Maltese cross formation in blood?

• A. Babesia microti
• B. Plasmodium vivax
• C. Helminthic larvae in blood
• D. Rickettsia species

Answer: (A)

The key idea here is that a Maltese cross formation inside red blood cells is a hallmark of a Babesia infection. Babesia microti is a tick-borne protozoan parasite that infects erythrocytes. When Babesia divides inside a red cell, the merozoites can arrange into a four-part tetrad, producing the characteristic Maltese cross on blood smear. The tick that commonly transmits this parasite is Ixodes scapularis, the same deer tick known for spreading Lyme disease and Anaplasma.

Plasmodium vivax, by contrast, is the malaria parasite transmitted by Anopheles mosquitoes, and its blood-stage forms do not create the Maltese cross. Rickettsia species are intracellular bacteria transmitted by ticks but do not parasitize red blood cells or produce Maltese cross formations. Helminthic larvae seen in blood are not associated with this Maltese cross finding either.

So, the presence of a Maltese cross in blood strongly points to Babesia microti transmitted by Ixodes scapularis.