A 32-year-old man from rural Odisha presents to the emergency department with a 5-day history of fever, chills, and headache. He reports that fever spikes occur every 48 hours, accompanied by rigors and profuse sweating. On examination, he is febrile (39.5°C), with mild splenomegaly and jaundice. His hemoglobin is 9.2 g/dL, platelet count is 65,000/μL, and serum bilirubin is 3.8 mg/dL (predominantly indirect). Peripheral blood smear shows ring forms and Schüffner's stippling. What is the most likely diagnosis?

Explanation

## Diagnosis: Plasmodium vivax Malaria ### Clinical Presentation **Key Point:** The 48-hour fever cycle (tertian fever) with rigors and profuse sweating is pathognomonic for *P. vivax* malaria. The patient presents with classic symptoms: fever spikes every alternate day (fever-free day in between), chills, and diaphoresis. ### Peripheral Blood Smear Findings | Feature | P. vivax | P. falciparum | P. malariae | P. ovale | |---------|---------|---------------|-------------|----------| | **Ring forms** | Present | Present (multiple rings/RBC) | Present | Present | | **Schüffner's stippling** | **Yes (prominent)** | Maurer's clefts | Absent | Schüffner's dots (finer) | | **RBC size** | **Enlarged** | Normal/slightly enlarged | Normal | Enlarged, fimbriated | | **Fever pattern** | **Tertian (48-hour)** | Quotidian/irregular | Quartan (72-hour) | Tertian (48-hour) | **High-Yield:** Schüffner's stippling is a hallmark of *P. vivax* and *P. ovale*. However, *P. vivax* causes **tertian fever** (48-hour cycle), while *P. ovale* is rare in India and causes milder disease with lower parasitemia. ### Laboratory Findings - **Hemoglobin 9.2 g/dL:** Mild anemia due to RBC destruction and bone marrow suppression - **Platelets 65,000/μL:** Thrombocytopenia is common in *P. vivax* (not just *P. falciparum*) - **Indirect hyperbilirubinemia 3.8 mg/dL:** Hemolysis from parasite rupture **Clinical Pearl:** *P. vivax* has a predilection for young RBCs (reticulocytes), leading to lower parasitemia levels (typically <1%) compared to *P. falciparum*, yet still causing significant hemolysis and jaundice. ### Why P. vivax? 1. **Tertian fever pattern** (48-hour cycle) — most specific finding 2. **Schüffner's stippling** on blood smear 3. **Splenomegaly and jaundice** — consistent with uncomplicated vivax malaria 4. **Geographic context** — Odisha is endemic for *P. vivax* 5. **Thrombocytopenia** — now recognized as common in vivax, not exclusive to falciparum **Mnemonic:** **VIVAX = Tertian (2-day) fever; FALCIPARUM = Quotidian (daily) or irregular; MALARIAE = Quartan (3-day) fever** ### Management - **First-line:** Artemisinin-based combination therapy (ACT) — Artemether + Lumefantrine or Dihydroartemisinin + Piperaquine - **Radical cure:** Primaquine 0.5 mg/kg/day × 14 days (after G6PD screening) to eliminate hypnozoites and prevent relapse - **Supportive care:** Fluid resuscitation, antipyretics, monitoring for severe malaria [cite:Harrison 21e Ch 217]