A 35-year-old immigrant from Sudan presents with intermittent fever, splenomegaly, and a peripheral blood film showing intraerythrocytic parasites with 'Maurer's clefts' visible inside infected red cells that are not enlarged. Some cells contain multiple ring forms ('appliqué' or accolé forms). The most appropriate next step in confirming the species is:

• A Thick film examination only, since Maurer's clefts unequivocally identify P. vivax
• B PCR-based species identification targeting 18S rRNA gene, as it distinguishes P. falciparum from P. knowlesi which can mimic band-form morphology ✓
• C Serological ELISA for circumsporozoite protein to differentiate P. malariae from P. falciparum
• D Giemsa-stained bone marrow biopsy showing band forms, which is diagnostic of P. malariae

Explanation

Maurer's clefts, non-enlarged red cells, multiple rings per cell, and appliqué forms are characteristic of Plasmodium falciparum, not P. vivax. However, P. knowlesi can show band forms resembling P. malariae on light microscopy and is potentially fatal; PCR targeting the 18S rRNA gene is now recommended by WHO to definitively distinguish P. falciparum from P. knowlesi and other species when morphology may be misleading. Thick film alone cannot replace PCR for species confirmation in equivocal cases. Bone marrow biopsy is not routinely indicated for malaria speciation.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.