A 50-year-old splenectomised man presents with intermittent fever, dark urine, and haemolytic anaemia requiring transfusion. He recalls multiple tick bites while working outdoors. Thin blood film shows small ring forms within erythrocytes arranged in tetrads resembling a Maltese cross, with no malarial pigment. Rapid malaria antigen tests are negative. The most likely causative agent is:

• A Plasmodium falciparum
• B Leishmania donovani
• C Trypanosoma cruzi
• D Babesia microti ✓

Explanation

Babesia microti, transmitted by Ixodes ticks, infects erythrocytes and characteristically forms tetrads called Maltese cross configurations, unlike any Plasmodium species. Absence of malarial pigment and negative rapid tests exclude falciparum malaria. Asplenia predisposes to severe babesiosis because the spleen normally clears infected red cells. Trypanosomes and Leishmania are extracellular or reticuloendothelial parasites and do not form intraerythrocytic tetrads.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.