Q: Please give information regarding morphological changes occurring in RBCs during malarial infection in humans. Are the affected RBCs heavier than normal RBCs? What is the specific gravity of normal matured RBCs?

A:The sequence of red cell invasion is probably similar for all Plasmodium sps and even though the parasites increase the permeability of RBC to get nutrients, yet the RBC structure is maintained for 48 hours. The growing parasite progressively consumes and degrades intracellular proteins, principally haemoglobin, resulting in formation of the malarial pigment and haemolysis of the infected red cell. This also alters the transport properties of the red cell membrane, and the red cell becomes more spherical and less elastic. P. falciparum malaria is characterised by development of sticky knobs on the surface of red cells, adhesion of red cells to the endothelial cells of post-capillary venules and formation of rosettes with uninfected cells. As the parasite matures, flexible biconcave disc becomes progressively more spherical and rigid. Reduced membrane fluidity, increasing sphericity, enlarging and relatively rigid intra-erythrocytic parasites make the red cells less filterable and cause obstruction at mid capillary level itself. The specific gravity of red cells is about 1.09