ABSTRACT
Malarial infection in man results from the bite of an infected female Anopheles mosquito in which the sporogonic cycle of development of the malarial parasite has taken place. Schizogony, or the asexual cycle (Figure 54.1), begins within the parenchymal cells of the liver. The exo-erythrocytic cycles within the liver result in the production of merozoites. This form of the malarial parasite then enters into red blood cells where it develops and multiplies asexually. This is termed the schizogonic erythrocytic cycle. The end product is the production of a new crop of merozoites, which are released through rupture from the cells and recommence the cycle. During the erythrocytic cycle a few parasites become differentiated into male and female gametocytes which are now present within the intravascular compartment awaiting ingestion by blood-sucking female Anopheles mosquitoes to complete their life cycle. Within the mosquitoes, fertilization occurs, with the production of the zygote. The zygote then undergoes successive stages of differentiation into an ookinete, which then penetrates the stomach wall of the mosquito to form an oocyst. From the mature oocyst sporozoites are liberated; these ultimately migrate to and reside within the salivary gland of the mosquito. They are then injected with the saliva into the human host at the time of a blood meal.
