The bite from an Anopheles mosquito carrying sporozoïtes in its salivary glands is one of the rare moments when the three players in malaria infection meet: a human being, the vector and the parasite. It is at this moment that a man is infected.  

The mobility of the sporozoïtes, although proven, is too slight to play a role in the transfer process from the vector to the host. The transfer of the sporozoïtes from the salivary glands to the human host, is considered to be passive, totally dependent on the access of the sporozoïtes to the saliva and from the flow of the latter during the bite. 

The number of sporozoïtes present in the salivary glands of an infected Anopheles mosquito may be highly variable, from a dozen to several hundreds of thousands. Generally, half of the Anopheles mosquitoes carry less than 1,000 sporozoïtes in their salivary glands. However, the number of sporozoïtes effectively injected into the host during the bite is astonishingly low, ranging from around a dozen to possibly several hundreds. This number of injected sporozoïtes represents around 1% of the number of sporozoïtes contained in the salivary glands.

The sporozoïtes injected into the skin during the penetration of the mouth parts (i.e. prior to the blood meal proper) would seem to be the only ones able to reach the host’s liver. The sporozoïtes injected into the blood vessel during blood meal have no future for the parasitic cycle for they are immediately re-ingested by the mosquito into its blood meal. It is for this reason that sporozoïtes are normally found in the stomach contents of an infectious and recently fed Anopheles mosquito.

The success of a single bite to infect a non-immune host is never absolute: although still imperfectly evaluated, it probably approaches 50%.

The biting behavior of the Anopheles mosquito with sporozoïtes in its salivary glands would seem to be modified, depending on the species of vectors and perhaps also according to the plasmodial species. An increase in the penetration time of the mouth parts may be observed and/or an increase in the average number of hosts bitten before the complete meal is eaten. These behavioral modifications in Anopheles mosquitoes would seem attributable to the presence of the parasite in the salivary glands: they clearly move in a direction which favors the transmission of the parasite.