Question
Life cycle of plasmodium falciparum.
Answer
The life cycle of Plasmodium falciparum spans a human intermediate host and the female Anopheles mosquito definitive host (where sexual reproduction occurs).
In the mosquito: an infective female Anopheles injects sporozoites into the human bloodstream while feeding.
Exoerythrocytic (hepatic) cycle: sporozoites travel to the liver and invade hepatocytes, undergoing schizogony to produce thousands of merozoites, released into the blood (unlike P. vivax/P. ovale, P. falciparum has no persistent hypnozoite stage, so relapse does not occur).
Erythrocytic cycle: merozoites invade RBCs (notably, all stages of RBC, unlike other species restricted to young or old cells, permitting very high parasitaemia), maturing through ring, trophozoite, and schizont stages; schizont rupture (roughly every 48 hours) releases new merozoites and pyrogenic toxins, producing periodic fever, and invades fresh RBCs. Infected RBCs develop surface knobs displaying PfEMP1, mediating cytoadherence/sequestration to vascular endothelium in deep capillaries (brain, placenta), removing mature parasite stages from peripheral blood and underlying severe complications (cerebral malaria, placental malaria).
Gametocytogenesis: some merozoites differentiate into male and female gametocytes (characteristically crescent/banana-shaped in P. falciparum) within RBCs.
In the mosquito (sexual cycle): ingested gametocytes fuse to form a zygote, developing into an ookinete, then an oocyst in the mosquito gut wall, ultimately releasing sporozoites that migrate to the salivary glands, completing the cycle.