Bit · Micro
Plasmodium Species — falciparum, vivax, ovale, malariae, knowlesi
Five species of malaria-causing protozoan. They share fever paroxysms but differ in severity, periodicity, and relapse biology.
Mechanism
Malaria is caused by Plasmodium protozoa transmitted by female Anopheles mosquitoes. Sporozoites travel to liver → schizonts → release merozoites that invade RBCs → cyclic hemolysis causes paroxysms of fever. Five human-infecting species:
Differentiator Table
| Species | Fever periodicity | Severity | RBC age preference | Relapse from liver? | Distinguishing features |
|---|---|---|---|---|---|
| P. falciparum | Irregular (24–48 h, no strict periodicity) | Severe — leading cause of malaria deaths | All ages | NO — no hypnozoites | Banana-shaped gametocytes; parasitized RBCs sequester in microvasculature → cerebral malaria, ARDS, AKI, severe anemia |
| P. vivax | Tertian (every 48 h) | Mild but relapsing | Young (reticulocytes) | YES (hypnozoites) | Schüffner dots; treat with primaquine to clear liver |
| P. ovale | Tertian (every 48 h) | Mild but relapsing | Young (reticulocytes) | YES (hypnozoites) | West Africa predominant; Schüffner dots; primaquine for liver |
| P. malariae | Quartan (every 72 h) | Chronic, mild | Old | No | Can persist for decades; chronic glomerulonephritis |
| P. knowlesi | Quotidian (every 24 h) | Variable, can be severe | All ages | No | Southeast Asia, zoonotic (macaques) |
The Pivot
Three questions:
- Severe presentation (cerebral malaria, ARDS, severe anemia)? → falciparum. Treat with IV artesunate.
- Fever every 48 h with relapses months/years later? → vivax or ovale. Treat acute illness with chloroquine (or artemisinin combination if resistant) + primaquine to clear liver hypnozoites. Check G6PD before primaquine.
- Fever every 72 h with chronic mild illness? → malariae.
NBME-Style Stem
A 28-year-old man returns from a 6-week trip to West Africa with cyclic fever, chills, and sweats every 48 hours. Peripheral blood smear shows parasitized erythrocytes that are enlarged and contain Schüffner dots. Which of the following is the most appropriate treatment regimen?
Concept Anchor
Five plasmodium species share the mosquito-to-liver-to-RBC cycle but differ in which RBCs they invade, how often the fever cycles, and whether liver hypnozoites linger. Only vivax and ovale need primaquine to prevent relapse.