A 24-year-old patient presents with a high-grade fever, headache, and weakness since 5 days. He gives a history of blood transfusion 4 months back. The microscopic examination of the thin blood smear is given below. What is the most probable causative agent?

The given clinical history and the microscopy showing maltese crosses or tetrads are suggestive of Babesiosis caused by Babesia microti. Babesiosis is caused by a group of protozoan organisms called Babesia species. Babesia microti: The definitive host is Ixodid ticks whereas the intermediate host is man. On microscopic examination, Babesia trophozoites appear as intraerythrocytic round or pyriform or ring form. The ring form is the most common and it lacks the central hemozoin deposit which differentiates it from P. falciparum. Other distinguishing features are the absence of schizonts and gametocytes and the presence of tetrads/maltose crosses, which are pathognomic of B. microti or B. duncani Reference: Paniker&;s Textbook of Medical Parasitology 8th edition