Question
Asexual life cycle of plasmodium vivax.
Answer
The asexual life cycle of Plasmodium vivax occurs in the human host, comprising an exoerythrocytic (hepatic) phase and an erythrocytic phase.
Exoerythrocytic (hepatic) cycle: an infective female Anopheles mosquito injects sporozoites into the bloodstream during a blood meal; sporozoites travel to the liver and invade hepatocytes, undergoing schizogony to produce thousands of merozoites. Distinctively for P. vivax (and P. ovale), a portion of the sporozoites remain dormant in the liver as hypnozoites, which can reactivate weeks to years later, causing relapse — a key clinical feature distinguishing P. vivax from P. falciparum (which has no hypnozoite stage).
Erythrocytic cycle: merozoites released from the liver invade red blood cells — P. vivax selectively invades young RBCs (reticulocytes) only (via the Duffy antigen receptor, explaining natural resistance in Duffy-negative individuals, common in parts of Africa), limiting the degree of parasitaemia compared to P. falciparum. Within the RBC, the parasite matures through ring → trophozoite → schizont stages; the trophozoite of P. vivax is classically described as amoeboid in shape, and infected RBCs show Schüffner’s dots (fine, granular, eosinophilic stippling) on Giemsa staining — a key morphological identifying feature. Schizont rupture (occurring roughly every 48 hours, giving the classical tertian periodicity) releases new merozoites (along with pyrogenic toxins triggering the periodic fever) that invade fresh reticulocytes, repeating the cycle.
Gametocytogenesis: some merozoites differentiate into male and female gametocytes (round/oval in shape for P. vivax, distinct from the crescent-shaped gametocytes of P. falciparum) within RBCs, which are infective to a mosquito taking a blood meal, initiating the sexual cycle within the mosquito (not part of the asexual cycle described here).
Clinical correlation: the 48-hour cyclical schizont rupture produces the classical tertian fever pattern (fever recurring every 48 hours, i.e., on alternate days) characteristic of vivax malaria (“benign tertian malaria”).