A 32-year-old male from rural Odisha presents with fever, chills, and sweating for 5 days. He reports that fever spikes occur every 48 hours with intervening afebrile periods. Physical examination reveals splenomegaly and mild jaundice. Thick blood smear shows ring forms and Schüffner's stippling. What is the most likely Plasmodium species responsible for this infection?

Explanation

## Clinical Presentation and Diagnosis **Key Point:** The 48-hour fever cycle (tertian fever) with intervening afebrile periods is pathognomonic for *P. vivax* and *P. ovale*. The presence of Schüffner's stippling on thick blood smear is a hallmark finding. ### Differential Features of Plasmodium Species | Feature | P. vivax | P. falciparum | P. malariae | P. ovale | |---------|----------|---------------|-------------|----------| | **Fever Pattern** | Tertian (48 hrs) | Quotidian/irregular | Quartan (72 hrs) | Tertian (48 hrs) | | **RBC Preference** | Young RBCs | All RBCs | Mature RBCs | Young RBCs | | **Schüffner's Stippling** | Present | Absent (Maurer's clefts) | Absent | Present | | **Ring Forms** | Yes | Yes (multiple) | Yes (rare) | Yes | | **Splenomegaly** | Common | Common | Rare | Common | | **Geographic Distribution** | Tropical/subtropical | Tropical | Temperate | Tropical/subtropical | **High-Yield:** *P. vivax* is the most common cause of malaria in India (70% of cases) and shows preference for young RBCs, explaining the lower parasitemia levels but higher clinical severity due to RBC destruction. ### Why This Case Points to P. vivax 1. **Tertian fever pattern (48-hour cycle):** Fever spikes every alternate day—classic for *P. vivax* and *P. ovale*. 2. **Schüffner's stippling:** Diagnostic feature visible on thick smear; indicates *P. vivax* or *P. ovale*. 3. **Ring forms with stippling:** Combination rules out *P. falciparum* (which shows Maurer's clefts, not Schüffner's stippling) and *P. malariae* (quartan fever, rare ring forms). 4. **Splenomegaly and jaundice:** Consistent with *P. vivax* hemolysis. 5. **Geographic origin (Odisha):** Endemic zone for *P. vivax* in India. **Clinical Pearl:** *P. vivax* causes relapsing malaria due to hypnozoites in hepatocytes; patients may have relapses weeks to months after initial infection if not treated with primaquine. **Mnemonic:** **VIVAX = VIral-like (tertian fever), Young RBCs, Vivid stippling (Schüffner's)** [cite:Park 26e Ch 8]