Causes of anemia in malaria infection

Haemolysis of infected red cells
Haemolysis of non-infected red cells (blackwater fever)
Dyserythropoiesis
Splenomegaly and sequestration
Folate depletion

After repeated infections partial immunity develops, allowing the host to tolerate parasitaemia with minimal ill effects. This immunity is lost if there is no further infection for a couple of years. Certain genetic traits also confer some immunity to malaria. People who lack the Duffy antigen on the red cell membrane (a common finding in West Africa) are not susceptible to infection with P. vivax. Certain haemoglobinopathies (including sickle cell trait) also give some protection against the severe effects of malaria: this may account for the persistence of these otherwise harmful mutations in tropical countries. Iron deficiency may also have some protective effect. The spleen appears to play a role in controlling infection, and splenectomized people are at risk of overwhelming malaria. Some individuals appear to have a genetic predisposition for developing cerebral malaria following infection with P. falciparum. Pregnant women are especially susceptible to severe disease.