Malaria represents the world’s greatest public health problem in terms of number of people affected, and the levels of morbidity and mortality. The protozoan malaria parasites (Plasmodium spp.) are transmitted by infected female mosquitoes when feeding on blood. Parasites soon enter liver cells, and after several days of multiplication, are released into the bloodstream where further cycles of asexual reproduction occur, giving rise to the clinical symptoms of malaria. Some erythrocytic parasites will differentiate into presexual forms (gametocytes; see Chapter 6), which when taken up by mosquitoes in further blood meals, mature into gametes and undergo a sexual cycle. With the eventual release of infective sporozoites into the mosquito salivary glands, the life cycle of the parasite is completed.