Malaria protozoa and red blood cells. Coloured scanning electron micrograph (SEM) of red blood cells (erythrocytes, red) and malarial merozoites (beige). Malaria is caused by Plasmodium sp. parasites, which are transmitted into the bloodstream by mosquito bites. The merozoite stage of this protozoan parasite invades red blood cells, replicating and destroying the cell upon release. The merozoites may then reinvade more red blood cells, causing the severe cyclic fevers of malaria. Magnification: x4000 when printed 10cm wide.