Malaria parasites. Light micrograph of red blood cells infected with malaria parasites (Plasmodium sp.). The sporozoite life stage of this parasite is injected into humans by a mosquito. The next stage, known as a trophozoite develops inside red blood cells (erythrocytes), and digests the haemoglobin in the cells, causing anaemia in the host. The trophozoites then replicate, releasing merozoites that invade other red blood cells. It is this periodic release of merozoites that causes the severe cyclic fevers of malaria. This blood is from a patient in Africa, where malaria is common.