Confirmed Plasmodium vivax Resistance to Chloroquine in Central Vietnam

Abstract

ABSTRACTPlasmodium vivaxresistance to chloroquine (CQ) is currently reported in almost all countries whereP. vivaxis endemic. In Vietnam, despite a first report onP. vivaxresistance to chloroquine published in the early 2000s,P. vivaxwas still considered sensitive to CQ. Between May 2009 and December 2011, a 2-year cohort study was conducted in central Vietnam to assess the recommended radical cure regimen based on a 10-day course of primaquine (0.5 mg/kg/day) together with 3 days of CQ (25 mg/kg). Here we report the results of the first 28-day follow-up estimating the cumulative risk ofP. vivaxrecurrences together with the corresponding CQ blood concentrations, among other endpoints. Out of 260 recruitedP. vivaxpatients, 240 completed treatment and were followed up to day 28 according to the WHO guidelines. Eight patients (3.45%) had a recurrentP. vivaxinfection, at day 14 (n= 2), day 21 (n= 1), and day 28 (n= 5). Chloroquine blood concentrations, available for 3/8 recurrent infections (days 14, 21, and 28), were above the MIC (>100 ng/ml whole blood) in all of these cases. Fever and parasitemia (both sexual and asexual stages) were cleared by day 3. Anemia was common at day 0 (35.8%), especially in children under 10 years (50%), and hemoglobin (Hb) recovery at day 28 was substantial among anemic patients (median change from day 0 to 28, +1.7 g/dl; interquartile range [IQR], +0.7 to +3.2). This report, based on CQ blood levels measured at the time of recurrences, confirms for the first timeP. vivaxCQ resistance in central Vietnam and calls for further studies using standardized protocols for accurately monitoring the extent and evolution ofP. vivaxresistance to chloroquine in Vietnam. These results, together with the mounting evidence of artemisinin resistance in central Vietnam, further highlight the increasing threat of antimalarial drug resistance to malaria elimination in Vietnam.