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Background  In the Greater Mekong sub-region,  Plasmodium vivax  has become the predominant species and imposes a major challenge for regional malaria elimination. This study aimed to investigate the variations in genes potentially related to drug resistance in  P. vivax  populations from the China–Myanmar border area. In addition, this study also wanted to determine whether divergence existed between parasite populations associated with asymptomatic and acute infections.    Methods  A total of 66  P. vivax  isolates were obtained from patients with acute malaria who attended clinics at the Laiza area, Kachin State, Myanmar in 2015. In addition, 102  P. vivax  isolates associated with asymptomatic infections were identified by screening of volunteers without signs or symptoms from surrounding villages. Slide-positive samples were verified with nested PCR detecting the 18S rRNA gene. Multiclonal infections were further excluded by genotyping at  msp - 3α  and  msp - 3β  genes. Parasite DNA from 60 symptomatic cases and 81 asymptomatic infections was used to amplify and sequence genes potentially associated with drug resistance, including  pvmdr1 ,  pvcrt - o ,  pvdhfr ,  pvdhps , and  pvk12 .    Results  The  pvmdr1  Y976 F  and F1076 L  mutations were present in 3/113 (2.7%) and 97/113 (85.5%)  P. vivax  isolates, respectively. The K10 insertion in  pvcrt - o  gene was found in 28.2% of the parasites. Four mutations in the two antifolate resistance genes reached relatively high levels of prevalence:  pvdhfr  S58 R  (53.4%), S117 N/T  (50.8%),  pvdhps  A383 G  (75.0%), and A553 G  (36.3%). Haplotypes with wild-type  pvmdr1  (976Y/997K/1076F) and quadruple mutations in  pvdhfr  (13I/57 L /58 R /61 M /99H/117 T /173I) were significantly more prevalent in symptomatic than asymptomatic infections, whereas the  pvmdr1  mutant haplotype 976Y/997K/1076 L  was significantly more prevalent in asymptomatic than symptomatic infections. In addition, quadruple mutations at codons 57, 58, 61 and 117 of  pvdhfr  and double mutations at codons 383 and 553 of  pvdhps  were found both in asymptomatic and symptomatic infections with similar frequencies. No mutations were found in the  pvk12  gene.    Conclusions  Mutations in  pvdhfr  and  pvdhps  were prevalent in both symptomatic and asymptomatic  P. vivax  infections, suggestive of resistance to antifolate drugs. Asymptomatic carriers may act as a silent reservoir sustaining drug-resistant parasite transmission necessitating a rational strategy for malaria elimination in this region.

malaria journal

Molecular surveillance for drug resistance markers in Plasmodium vivax isolates from symptomatic and asymptomatic infections at the China–Myanmar border