Fig. 1.

Life cycle of the malaria parasite. (1) Sporozoites are injected into a vertebrate host during the blood meal of a female anopheline mosquito and rapidly invade hepatocytes. One sporozoite can develop into 20 000 merozoites, which rupture from the hepatocyte, enter the bloodstream and invade erythrocytes. (2) In the asexual erythrocytic cycle, merozoites invade erythrocytes and mature from ring stages to schizonts within these cells in 48–72 h, the time varying with the species of malaria parasite. (3) Some erythrocytic stages differentiate into gametocytes, which are infective for mosquitoes. Fertilization occurs in the mosquito midgut, and within 24 h zygotes transform into ookinetes, which penetrate the midgut and form oocysts. Sporozoites rupture from these oocysts and invade the salivary glands of the mosquito from where they are injected into a vertebrate host.