The malaria parasite is transmitted to humans (R) by a female Anopheles mosquito when she takes a blood meal to feed her young. The parasites are rapidly taken up into the cells of the liver where they become schizonts (A), multiply and go on to invade blood cells. Current medicines mostly kill malaria parasites at this blood stage. This is when the parasite is at its most abundant – up to 1012 parasites in one person (B) and the stage that leads to clinical symptoms of malaria.
Some of the blood-stage parasites develop into male and female gametocytes (see dotted line and C) which are taken up into the mosquito gut during her blood meal (likely a different mosquito). In the gut these gametocytes become gametes and fuse. This is the sexual stage of the lifecycle. To eradicate malaria we also need medicines that can stop the parasite at this stage (C to F) thereby stopping transmission. This is also the most efficient stage to target as there are fewer parasites to kill, with density as low as 10, in one cycle of infection.