Objective: Mutations in the pvmdr1 gene have been recognized as a possible molecular marker of chloroquine resistance. The aim of this study was to investigate the genotypes of pvmdr1 in P. vivax isolates from Thailand.
Materials and Methods: A total of 32 P. vivax-positive blood samples were collected from two high malaria-endemic areas
of Thailand, 20 samples from Yala and 12 from Kanchanaburi provinces. The pvmdr1 polymorphisms were determined
using direct sequencing of nested PCR products.
Results: The pvmdr1 gene mutation was found in 71.9% of 32 isolates. The four pvmdr1 polymorphic sites composed of
Y976F, F1076L and two novel mutations of D932Y and V1008. The double mutation (Y976F-F1076L) was the predominant
strain (53.1%). The single mutation (F1076L) represented 12.5%, and the two novel mutants represented 3.1% each. In Yala, 80% of the isolates carried the pvmdr1 mutation and two genotypes detected were F1076L (15%) and Y976F-F1076L (65%). In Kanchanaburi, 58.3% of isolates were pvmdr1 mutants and four genotypes including Y976F-F1076L (33.3%), F1076L (8.3%), V1008-F1076L (8.3%) and D932Y-Y976F-F1076L (8.3%) were found.
Conclusion: A high prevalence of pvmdr1 gene mutation in this study provides valuable information regarding the awareness of P. vivax chloroquine resistance spreading in Thailand. The two novel mutations should be noted.

Keywords: Plasmodium vivax, pvmdr1, Chloroquine resistance, Malaria, Thailand