from Amy Kristine Bei and Manoj Theodore Duraisingh writing in Malaria Parasites: Comparative Genomics, Evolution and Molecular Biology:
The first challenge faced by the invasive merozoite form of the Plasmodium parasite when released into the bloodstream is to invade and establish itself within a host erythrocyte. Following hepatic schizont rupture, merozoites are released into the circulation and must successfully locate, bind to, and invade an erythrocyte lest they are cleared by the immune system. Subsequent cycles of erythrocytic egress, invasion and growth result in the escalation of parasitemia, often associated with clinical symptoms. The parasite has developed molecular strategies that allow it to invade the host cell while avoiding the attack of the immune system and in response to diversity of the receptor repertoire of its human host. Depending on the species, there is a limited window of time in which the merozoite remains viable for invasion. The invasive potential of the merozoite is influenced by three levels of host cell selection: 1) selection between host species (species specific tropism), 2) selection among individuals within a host species (erythrocyte receptor diversity), and 3) selection of subpopulations within an individual (age dependent invasion). The host-parasite interactions that allow for efficient host cell selection and invasion of erythrocytes will be the topic addressed by this chapter.