Subjects who were previously enrolled into study A that received a single dose of 600 mg chloroquine base will receive a single dose of piperaquine phosphate (in form of 120/960 mg dihydroartemisinin-piperaquine) in this study. The subjects who were previously enrolled into study B that received a single dose of piperaquine phosphate (in form of 120/960 mg dihydroartemisinin-piperaquine) will receive a single dose of 600 mg of chloroquine base in this study.