A 32-year-old woman from rural Odisha presents to the emergency department with a 5-day history of high-grade fever with chills and rigors. She reports that the fever spikes every 48 hours, accompanied by severe headache, myalgia, and vomiting. On examination, she is febrile (39.5°C), with mild jaundice, hepatomegaly (2 cm below costal margin), and splenomegaly (3 cm below costal margin). Her blood smear shows ring forms and Schüffner's stippling. Hemoglobin is 9.2 g/dL, platelet count 45,000/μL, and serum creatinine 1.8 mg/dL. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Plasmodium vivax Malaria ### Key Clinical Features **Key Point:** The 48-hour fever cycle (tertian fever) with ring forms and Schüffner's stippling on blood smear is pathognomonic for *Plasmodium vivax* infection. **High-Yield:** *P. vivax* characteristically causes: - **Tertian fever pattern** (fever every 48 hours) — occurs when erythrocytes rupture synchronously - **Ring forms** on blood smear (young trophozoites) - **Schüffner's stippling** — cytoplasmic dots visible with Romanowsky stain, indicating infected RBC membrane changes - **Preference for young RBCs** — hence lower parasitemia density than *P. falciparum* ### Why This Patient Has Severe Malaria Despite P. vivax **Clinical Pearl:** Although *P. vivax* is traditionally considered "benign malaria," severe complications including acute kidney injury, thrombocytopenia, and cerebral involvement are increasingly recognized, particularly in endemic regions. ### Laboratory Correlation | Finding | Explanation | | --- | --- | | Hemoglobin 9.2 g/dL | Hemolysis + bone marrow suppression | | Platelets 45,000/μL | Immune-mediated destruction + sequestration | | Creatinine 1.8 mg/dL | Acute tubular necrosis from hemoglobinuria, hypotension, cytokine storm | | Jaundice | Unconjugated hyperbilirubinemia from hemolysis | | Hepatosplenomegaly | Erythrophagocytosis + immune activation | **Mnemonic: VIVAX FEATURES** — **V**ertigo/Vivid symptoms, **I**nfects young RBCs, **V**ascular sequestration (less), **A**cute kidney injury (emerging), **X**-ray (Schüffner's stippling) ### Management Implications This patient requires: 1. **Artemisinin-based combination therapy (ACT)** — artemether or artesunate IV given severe disease 2. **Supportive care** — fluid resuscitation (cautious given AKI), transfusion if Hb <7 g/dL, dialysis if needed 3. **Monitoring** — daily parasitemia, renal function, platelet count 4. **Primaquine** — 0.5 mg/kg/day for 14 days post-acute phase to eliminate hypnozoites (after G6PD testing) [cite:Harrison 21e Ch 218]