Genetic diversity of the Plasmodium vivax multidrug resistance 1 gene in Thai parasite populations

Abstract

Plasmodium vivax resistance to chloroquine (CQ) was first reported over 60 years ago. Here we analyzed sequence variations in the multidrug resistance 1 gene (Pvmdr1), a putative molecular marker for P. vivax CQ resistance, in field isolates collected from three sites in Thailand during 2013-2016. Several single nucleotide polymorphisms previously implicated in reduced CQ sensitivity were found. These genetic variations encode amino acids in the two nucleotide-binding domains as well as the transmembrane domains of the protein. The high level of genetic diversity of Pvmdr1 provides insights into the evolutionary history of this gene. Specifically, there was little evidence of positive selection at amino acid F1076L in global isolates to be promoted as a possible marker for CQ resistance. Population genetic analysis clearly divided the parasites into eastern and western populations, which is consistent with their geographical separation by the central malaria-free area of Thailand. With CQ-primaquine remaining as the frontline treatment for vivax malaria in all regions of Thailand, such a population subdivision could be shaped and affected by the current drugs for P. falciparum since mixed P. falciparum/P. vivax infections often occur in this region.

Evolution of the Plasmodium vivax multidrug resistance 1 gene in the Greater Mekong Subregion during malaria elimination

“…However, the F1076L mutation in the longitudinal samples from the China-Myanmar border had an increasing trend in prevalence; its frequency reached 77.8% in 2015, almost doubled from that (41.7%) in 2012-2013. Interestingly, this mutation had a moderate prevalence in the Thailand-Myanmar border area (~30-62%) over the period of 2008-2016 and in Ubon Ratchathani (28%), but it almost reached fixation in Chanthaburi Province at the Thailand-Cambodia border [33,62]. Conversely, the prevalence of the Y976F mutation in the China-Myanmar border populations progressively decreased and was not detected in the 2015 samples.…”

“…MN892092-MN892220; MN892221-MN892236; and MN892237-MN892275. In addition, 98 Pvmdr1 sequences from parasites collected in western (Tak and Kanchanaburi provinces) and eastern Thailand (Ubon Rachathani Province) were also used for analysis [33]. All sequences were aligned with the reference Pvmdr1 sequence from the Salvador I strain (PVX_080100) using Clustal Muscle 3.8 [38] incorporated in the MEGA7 software [39].…”

“…In light of the deteriorating CQ clinical efficacy for treating vivax malaria at the China-Myanmar border [35], we followed the evolution of the Pvmdr1 gene in parasite populations from this region over a seven-year period and sequenced the full-length Pvmdr1 gene in 275 P. vivax clinical samples. To put this study in context with parasites from other regions in the GMS, we also analyzed 98 Pvmdr1 sequences from the western and eastern borders of Thailand [33]. For the longitudinal P. vivax clinical samples from the China-Myanmar border, 27 isolates collected in 2008 harbored 22 SNPs, of which 20 are nonsynonymous.…”

“…In comparison, none of these mutations were selected in the central China population (Table 4). It is noteworthy that of the two mutations M908L and T958M associated with reduced in vitro CQ sensitivity [28] and also highly prevalent in Thailand [33], M908L was positively selected in the China-Myanmar border parasites but not in the Thailand-Myanmar or the Thailand-Cambodia border parasite populations (Table 4). Furthermore, most of mutations with frequencies of ≥ 5% such as A861E, L845F, and K1393N (Table 1) were also selected in the China-Myanmar parasites (Table 4).…”

“…For instance, dihydropteroate synthase and dihydrofolate reductase genes that are associated with resistance to antifolate drugs were found to be selected in P. vivax [31]. In the GMS, P. vivax parasites were found to exhibit high levels of genetic diversity in Thailand [33], southern China, and Myanmar [34]. In this study, we focused on the genetic diversity of the Pvmdr1 gene in the vivaxendemic area along the China-Myanmar border, hoping to understand the evolution of the parasites amid the falling CQ treatment efficacy [35] and increased proportions of vivax malaria in most areas of the GMS [3].…”