The simultaneous occurrence of severe vivax disease and CQ-resistance in some countries has raised the question of a possible association between severity and resistance, especially for anaemia [170] . CQ resistance actually has been reported in Brazil almost at the same time as clinical severity [171, 172] , but some studies argue against that, showing that severe patients responded to CQ [45] . Added to that, reliable genetic markers of resistance are lacking [173] . Increased levels of pvmdr-1 and pvcrt-o RNA in a single severe patient with vivax malaria however paved the way to the study of gene expression in association to resistance [174] .