Within the red blood cells, the parasites multiply. Further again, periodically breaking out of their host asexually to invade fresh red blood cells. Several such amplification cycles occur. Thus classical descriptions of waves of fever arise from simultaneous waves of merozoites escaping and infecting red blood
cells. In P.vivax and possibly P.ovale, the liver forms of the parasite sometimes may develop into a dormant form called hypnozoites. After a period of dormancy, they reactivate and produce merozoites. Thus, Hypnozoites are responsible for long incubation and late relapse in these two species of malaria parasite. (Cogswell, 1992).
The parasite is relatively protected from attack by the body’s immune system because for most of its human life cycle it resides within the liver and blood cells and is relatively invisible to immune surveillance. However, circulating infected blood cells are destroyed in the spleen. To avoid this fate, the P. falciparum parasite displays adhesive proteins on the surface of the infected blood cells, causing the blood cells to stick to walls of small blood vessels, thereby sequestering the parasite from passage through the general circulation and the spleen (Chen et al, 2000). This “Stickiness” is the main factor giving rise to haemorrhagic complication of malaria. High endothelial venules which are the smallest branches of the circulatory system can be blocked by the attachment of masses of these infected red blood cells. The blockage of these vessels causes symptom such as seen in placental and cerebral malaria. In cerebral malaria, the sequestrated red blood cells can breach the blood brain barrier and possibly lead to coma (Adams et al, 2002).
Some merozoites differentiate into male and female gametocytes. If a mosquito pierces the skin of an infected person, it potentially picks up gametocytes within the blood. Fertilization and sexual recombination of the parasite occurs in the mosquito’s gut, thereby defining it as the definitive host of the disease. New sporozoites develop and travel to the mosquito’s salivary gland, completing the cycle.
It has been observed that pregnant women are especially attractive to mosquitoes (Lindsay et al., 2000) and malaria in pregnancy is an important cause of stillbirths, infant mortality and low birth weight (VanGeertruyden et al., 2004) particularly in P.falciparum infection, but also in other specie infection, such as P.vivax (Rodriguez-Morales et al., 2006).
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