Fig. 2: The plasmodia life cycle. The human (asexual) stage of the life cycle begins with the exoerythrocytic phase. When an infected mosquito bites a human, sporozoites in the mosquito's saliva enter the bloodstream (1). The sporozoites travel to the liver, where they invade hepatocytes (2); over a period of up to 4 weeks, the infected hepatocytes mature into schizonts. In Plasmodium vivax and P. ovale infections only, some schizonts may remain dormant as hypnozoites (3) for weeks to years before causing clinical relapses. With schizont rupture, merozoites are released into the bloodstream (4). In the erythrocytic phase, merozoites invade erythrocytes and either undergo an asexual cycle of reproduction (5) or develop into nonmultiplying sexual forms (gametocytes) (6). These gametocytes are crucial for perpetuating the life cycle, as they are ingested by a feeding mosquito (7) and undergo sexual reproduction within the mosquito midgut; thousands of infective sporozoites (8) are produced, which then migrate to the salivary glands, ready to initiate another life cycle. Photo: Lianne Friesen and Nicholas Woolridge