Malaria parasites. Coloured scanning electron micrograph (SEM) of malaria parasites (Plasmodium sp., green) bursting from the surface of a culture cell (brown). These protozoans are transmitted to humans by infected mosquitoes when they drink blood. They travel through the bloodstream to the liver where they multiply inside liver cells, before moving back into the bloodstream to infect red blood cells. A cycle of fever, the main symptom of the disease, is caused by the rupture of infected red blood cells. Malaria is treated with antimalarial drugs such as quinine. Magnification: x7600 at 6x7cm size.