Plasmodium falciparum malaria in Laos: Chloroquine treatment outcome and predictive value of molecular markers

A 28-day treatment trial was undertaken, to determine the efficacy of chlor oquine in Laos and to assess the predictive value of molecular markers (cg2 , pfmdr1, and pfcrt) that were previously linked to chloroquine resistance. In total, 522 febrile patients were screened for falciparum malaria by rap id diagnostic assays. Of 81 patients (15.5% prevalence) who were positive b y the assays and microscopy, 48 were eligible to participate in the 28-day trial. Nine patients defaulted. Chloroquine cured 54% (95% confidence inter val, 45.8-61.8) of falciparum-infected patients. Of 18 (46%) patients with treatment failure, 13 (72%) experienced high-grade resistance. Polymorphism s in cg2 and the N86Y mutation in PfMDR1 were not predictive of treatment o utcome. A mutation in PfCRT (K76T) was perfectly associated with in vivo ch loroquine resistance. However, K76T was also present in in vivo-sensitive i solates, which suggests that the presence of this mutation was necessary, b ut not sufficient, to predict in vivo outcome in this cohort.