## Plasmodium vivax — Blood Smear Morphology ### Characteristic Features of P. vivax **Key Point:** Maurer's clefts are a distinctive feature of *Plasmodium falciparum*, NOT P. vivax. This is a high-yield distinction on peripheral blood smears. **High-Yield:** P. vivax displays the following on Romanowsky-stained blood smear: | Feature | P. vivax | P. falciparum | |---------|---------|---------------| | **Stippling pattern** | Schüffner's stippling (fine, dots) | Maurer's clefts (coarse, comma-shaped) | | **RBC enlargement** | Marked (1.5–2× normal) | Normal or slightly enlarged | | **RBC distortion** | Significant (oval, irregular) | Minimal | | **Ring forms** | Large, prominent | Small, delicate | | **Trophozoites** | Amoeboid, active | Compact, less motile | ### Why Schüffner's Stippling? 1. Fine cytoplasmic dots appear on RBC surface when stained with Romanowsky dyes 2. Caused by parasitic protein deposits in the RBC membrane 3. Visible only in P. vivax and P. ovale (and P. malariae to a lesser extent) **Clinical Pearl:** On a blood smear, if you see Schüffner's stippling + enlarged RBC + amoeboid trophozoites = P. vivax. If you see Maurer's clefts + normal RBC size + small ring forms = P. falciparum. **Mnemonic:** **"Vivax = Schüffner's; Falciparum = Maurer's"** — the stippling pattern is the quickest way to differentiate these two species on smear. ### Why Other Options Are Correct for P. vivax - **Schüffner's stippling:** Pathognomonic for P. vivax (and P. ovale) - **Enlarged, distorted RBCs:** P. vivax preferentially infects young RBCs (reticulocytes), causing marked enlargement and irregular shape - **Ring forms and trophozoites:** Both are readily visible in P. vivax parasitemia [cite:Park 26e Ch 7]
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