In Plasmodium falciparum infection, describe the hepatic and erythrocytic stages and where each occurs.

• A. Sporozoites invade erythrocytes directly, forming erythrocytic schizonts; merozoites released into the bloodstream invade red blood cells and progress through ring, trophozoite, and schizont stages.
• B. Sporozoites invade hepatocytes forming hepatic schizonts; merozoites released into the bloodstream invade red blood cells and progress through ring, trophozoite, and schizont stages; sexual forms (gametocytes) mature in RBCs.
• C. Sporozoites invade kidney cells; merozoites invade lymphocytes; RBCs not involved.
• D. Merozoites invade hepatocytes; sporozoites invade red blood cells; merozoites form hepatic schizonts.

Answer: (B)

The key idea is the sequence and location of parasite development in malaria. After a mosquito transmits sporozoites, they travel to the liver and invade hepatocytes, where they develop into hepatic schizonts that release merozoites into the bloodstream. These merozoites then invade red blood cells and begin the erythrocytic cycle, progressing inside the RBCs through ring, trophozoite, and schizont stages. When RBC schizonts rupture, new merozoites are released to infect more RBCs, and some of these develop into gametocytes that mature within circulating red blood cells. This explains why symptoms come from the blood stage, while the liver stage is clinically silent. In Plasmodium falciparum there is no dormant hepatic stage (unlike P. vivax/ovale), and the sexual forms mature in RBCs.