Parasites replicate by mitosis, producing progeny cells which are genetically identical to each other and to the parent parasite. This replication is known as asexual reproduction. During an infection, a small proportion of parasites do not divide, but instead develop as sexual stages called gametocytes. This development occurs over 7 to 10 days within a red blood cell. When a mosquito takes a bloodmeal, parasites will be taken up into the mosquito gut.
Gametocytes present emerge from their red cell hosts, and become haploid gametes.
A male and a female gamete fertilise to become a diploid zygote, called an ookinete. This is the only diploid stage of the parasite's lifecycle. The ookinete moves through the bloodmeal, crossing the peritrophic matrix surrounding the blood bolus, and penetrates the mosquito midgut epithelium. It then encysts on the outer wall of the midgut, and develops over the next 7 to 14 days as an oocyst. Sporozoites develop within the oocyst and migrate in haemolymph to invade the salivary glands.