A 28-year-old male from rural Bihar presents with fever, chills, and sweating for 3 days. He reports a history of similar episodes occurring every 48 hours over the past 2 weeks. On examination, he is febrile (39.5°C) and has mild hepatosplenomegaly. A peripheral blood smear prepared during fever shows ring forms and Schüffner's stippling within RBCs. What is the most likely diagnosis?

## Diagnosis: Plasmodium vivax Malaria ### Clinical Presentation **Key Point:** The 48-hour fever cycle (tertian fever) is pathognomonic for P. vivax and P. ovale, distinguishing it from P. falciparum (irregular) and P. malariae (72-hour, quartan). ### Peripheral Blood Smear Findings | Feature | P. vivax | P. falciparum | P. malariae | | --- | --- | --- | --- | | **Ring forms** | Present (early) | Present (multiple, thin) | Present (single, thick) | | **Schüffner's stippling** | Prominent, coarse | Maurer's clefts (finer) | Absent or fine | | **RBC size** | Enlarged (1.5–2× normal) | Normal to slightly enlarged | Normal | | **Fever pattern** | Tertian (48 hrs) | Irregular/quotidian | Quartan (72 hrs) | | **Gametocytes** | Oval, fill RBC | Crescent-shaped | Round | **High-Yield:** Schüffner's stippling is a hallmark of P. vivax—coarse dots visible on Romanowsky staining that represent cytoplasmic inclusions. This finding is diagnostic when present. ### Geographic & Epidemiologic Context **Clinical Pearl:** P. vivax is endemic in rural Bihar and is the most common malaria species in India outside high-transmission zones. The history of relapsing fevers over 2 weeks suggests hypnozoite reactivation, which is characteristic of P. vivax. ### Why This Case Fits P. vivax 1. Tertian fever (48-hour cycle) 2. Schüffner's stippling on smear 3. Hepatosplenomegaly (mild) 4. Endemic area (rural Bihar) 5. Enlarged RBCs with ring forms **Mnemonic:** **VIVAX = Vivid fever pattern (tertian), Stippling visible (Schüffner's), Enlarged RBCs** [cite:Chatterjee's Textbook of Parasitology Ch 4]