Jessica T. LinJaymin C. PatelOksana KharaboraJetsumon SattabongkotSinuon MuthRatawan UbaleeAnthony L. SchusterWilliam O. RogersChansuda WongsrichanalaiJonathan J. JulianoUniversity of North Carolina School of MedicineThe University of North Carolina at Chapel HillMahidol UniversityNational Malaria CenterArmed Forces Research Institute of Medical Sciences, Thailand2018-10-192018-10-192013-06-01American Journal of Tropical Medicine and Hygiene. Vol.88, No.6 (2013), 1116-1123000296372-s2.0-84878603905https://repository.li.mahidol.ac.th/handle/123456789/31916Plasmodium vivax accounts for an increasing fraction of malaria infections in Thailand and Cambodia. We compared P. vivax genetic complexity and antimalarial resistance patterns in the two countries. Use of a heteroduplex tracking assay targeting the merozoite surface protein 1 gene revealed that vivax infections in both countries are frequently polyclonal (84%), with parasites that are highly diverse (HE = 0.86) but closely related (GST = 0.18). Following a history of different drug policies in Thailand and Cambodia, distinct patterns of antimalarial resistance have emerged: most Cambodian isolates harbor the P. vivax multidrug resistance gene 1 (pvmdr1) 976F mutation associated with chloroquine resistance (89% versus 8%, P < 0.001), whereas Thai isolates more often display increased pvmdr1 copy number (39% versus 4%, P < 0.001). Finally, genotyping of paired isolates from individuals suspected of suffering relapse supports a complex scheme of relapse whereby recurrence of multiple identical variants is sometimes accompanied by the appearance of novel variants. Copyright © 2013 by The American Society of Tropical Medicine and Hygiene.Mahidol UniversityImmunology and MicrobiologyMedicineArticleSCOPUS10.4269/ajtmh.12-0701