Javlington t1_j95oeie wrote

Specifically in the case of Malaria, the fever bouts come and go because the parasite migrates between the centre of your body and the periphery, depending on whether it wants to be picked up by mosquitos. Besides this, it changes its immune epitopes on the reg, trying to fool your immune system which attempts to learn but gets confused by the constant changes on the surface of the parasite individuals.