Red blood cells with malaria, computer artwork. Malaria is caused by the Plasmodium parasite, which is transmitted into the bloodstream by mosquito bites. The merozoite stage of this protozoan parasite (seen here) invades red blood cells, replicating and destroying the red blood cell upon release. This can cause anaemia. The merozoites may then reinvade more red blood cells, causing the severe cyclic fevers of malaria.