File:Determinants-of-relapse-periodicity-in-Plasmodium-vivax-malaria-1475-2875-10-297-23.jpg

English: Relapse pre-empts the emergence of de-novo anti-malarial drug resistance. De-novo drug resistance is a rare event and usually there is only one mutant resistant parasite which multiplies while the sibling drug sensitive parasite population declines (green) [160]. Only a highly resistant parasites' progeny (red line) can reach transmissible densities in blood (total numbers circa 100,000,000 in the body) before the relapse (comprising drug sensitive parasites) becomes patent and the consequent illness (and any treatment effect) suppresses multiplication. Slowly eliminated anti-malarial drugs reduce this protective effect by reducing multiplication of the relapse parasites more than multiplication of the de-novo resistant parasites.