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BACKGROUND:Plasmodium vivax is the main cause of malaria in Nepal. Relapse patterns have not been characterized previously. METHODS:Patients with P. vivax malaria were randomized to receive chloroquine (CQ; 25 mg base/kg given over 3 days) alone or together with primaquine (PQ; 0.25 mg base/kg/day for 14 days) and followed intensively for 1 month, then at 1- to 2-month intervals for 1 year. Parasite isolates were genotyped. RESULTS:One hundred and one (49%) patients received CQ and 105 (51%) received CQ + PQ. In the CQ + PQ arm, there were 3 (4.1%) recurrences in the 73 patients who completed 1 year of follow-up compared with 22 of 78 (28.2%) in the CQ-only arm (risk ratio, 0.146 [95% confidence interval, .046-.467]; P < .0001). Microsatellite genotyping showed relatively high P. vivax genetic diversity (mean heterozygosity, 0.843 [range 0.570-0.989] with low multiplicity of infection (mean, 1.05) reflecting a low transmission preelimination setting. Of the 12 genetically homologous relapses, 5 (42%) occurred in a cluster after 9 months, indicating long latency. CONCLUSIONS:Although there may be emerging CQ resistance, the combination of CQ and the standard-dose 14-day PQ regimen is highly efficacious in providing radical cure of short- and long-latency P. vivax malaria in Nepal.

Original publication





The Journal of infectious diseases

Publication Date





448 - 456


Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.


Humans, Plasmodium vivax, Malaria, Vivax, Chronic Disease, Recurrence, Chloroquine, Primaquine, Antimalarials, Drug Therapy, Combination, Longitudinal Studies, Follow-Up Studies, Prospective Studies, Genotype, Adolescent, Adult, Middle Aged, Nepal, Female, Male, Young Adult