Abstract
Chloroquine (CQ) is used to treat Plasmodium vivax malaria in areas where CQ resistance has not been reported. The use of artemisinin (ART)-based combination therapies (ACTs) to treat CQ-sensitive P. vivax infections is effective and convenient but may promote the emergence and worsening of ART resistance in sympatric Plasmodium falciparum populations. Here, we show that CQ effectively treats P. vivax malaria in Pursat Province, western Cambodia, where ART-resistant P. falciparum is highly prevalent and spreading. (This study has been registered at ClinicalTrials.gov under registration no. NCT00663546.).