The infection of a female Anopheles mosquito starts with a blood meal taken from a human carrier of malaria-infected gametocytes. If parasites at other stages of their development are ingested by the mosquito, they are killed and digested. The gametocyte stage is haploid, as are all the stages in Man. It is present in the peripheral blood in both male and female forms, ordinarily in the proportion of one male for three females.

The gametocytes starts a process of activation inside the stomach of the mosquito. They take on a spherical shape and the erythrocytic plasmatic membrane ruptures. The activated female gametocyte is called a macrogamete. The male gametocyte undergoes an exflagellation, a process during which flagella grow out from the original cell (up to eight, but ordinarily from four to six), which subsequently break away from the body of the activated male gametocyte and constitute as many microgametes. All these transformations occur ten or so minutes after the blood meal. The male gamete moves under its own power, meets a female gamete which it subsequently penetrates. This fecundation process ends with the formation of a diploid egg of spherical shape. A dozen or so hours after the infesting meal, this egg then becomes an ookinete, via an intermediate stage referred to as a "retort": during which what is not yet an ookinete grows from what is already no longer an egg. This ookinete is elongated in shape and presents the characteristics of an invasive stage. It moves under its own power towards the edge of the stomach, penetrates through the peritrophic envelope (extracellular structure produced by the stomach and enveloping the whole of the food vacuole), then forces its way through the epithelial cells to the outer surface of the stomach to finally come to a halt under the vitreous lamella of the epithelium. There, the ookinete rounds up to a small sphere called an oocyst. This oocyst grows considerably for around ten days undergoing numerous nuclear divisions, the first of which is reductional. On the inside of the oocyst some 10,000 sporozoïtes develop and when mature are released, when the oocyst ruptures, to find themselves in the hemolymph of the mosquito, then throughout its body cavity. These trophozoïtes have a positive tropism for the salivary glands into which they penetrate, passing through the epithelium of the salivary glands and ending up in the salivary duct, ready to be injected with the saliva during the next blood meal. It would seem to be accepted that an Anopheles mosquito with sporozoites in its salivary glands remains infective throughout its life.

At least six factors can be individualized: 

In the current state of knowledge, only a negative response can be given to this question, at least for Anopheles gambiae, which would seem to tolerate perfectly Plasmodium falciparum. The sporogonic development of the parasite and its continued presence at the sporozoïte stage in the salivary glands would not seem to have any repercussions on the survival of the infected mosquito. A low teratogenic effect should not, however, be excluded, but would be without any major epidemiological implication. Such an effect would explain, for example, why in Nature only rarely is an Anopheles mosquito observed with a large number of oocysts, while in the insectarium, this phenomenon is observed frequently. Moreover, there is the assurance that certain plasmodial species which do not parasitize humans are effectively pathogenic for their vectors.