Substantial population structure of <i>Plasmodium vivax</i> in Thailand facilitates identification of the sources of residual transmission

<div><p>Background</p><p><i>Plasmodium vivax</i> transmission in Thailand has been substantially reduced over the past 10 years, yet it remains highly endemic along international borders. Understanding the genetic relationship of residual parasite populations can help track the origins of the parasites that are reintroduced into malaria-free regions within the country.</p><p>Methodology/Results</p><p>A total of 127 <i>P</i>. <i>vivax</i> isolates were genotyped from two western provinces (Tak and Kanchanaburi) and one eastern province (Ubon Ratchathani) of Thailand using 10 microsatellite markers. Genetic diversity was high, but recent clonal expansion was detected in all three provinces. Substantial population structure and genetic differentiation of parasites among provinces suggest limited gene flow among these sites. There was no haplotype sharing among the three sites, and a reduced panel of four microsatellite markers was sufficient to assign the parasites to their provincial origins.</p><p>Conclusion/Significance</p><p>Significant parasite genetic differentiation between provinces shows successful interruption of parasite spread within Thailand, but high diversity along international borders implies a substantial parasite population size in these regions. The provincial origin of <i>P</i>. <i>vivax</i> cases can be reliably determined by genotyping four microsatellite markers, which should be useful for monitoring parasite reintroduction after malaria elimination.</p></div

Genetic differentiation (<i>Fst</i>) of <i>P</i>. <i>vivax</i> populations.

<p>Genetic differentiation (<i>Fst</i>) of <i>P</i>. <i>vivax</i> populations.</p

Optimal panel of MS markers and determination of haplotype loss during the removal of each MS.

<p>The removal of MS was prioritized from lower to higher <i>H</i>_<i>E</i> according to the X-axis. The remaining haplotypes after removal were shown by the percentages of all haplotypes.</p

Map showing three provinces in Thailand where samples were collected (modified from https://commons.wikimedia.org/wiki/Atlas_of_Thailand).

<p>Map showing three provinces in Thailand where samples were collected (modified from <a href="https://commons.wikimedia.org/wiki/Atlas_of_Thailand" target="_blank">https://commons.wikimedia.org/wiki/Atlas_of_Thailand</a>).</p

Genetic differentiation (<i>Fst</i>) of <i>P</i>. <i>vivax</i> populations.

<p>Genetic differentiation (<i>Fst</i>) of <i>P</i>. <i>vivax</i> populations.</p

Minimum spanning tree of parasite genotypes constructed using the goeBURST algorithm.

<p>Each circle represents a haplotype. Colors indicate the different provinces where the parasites were collected. Sizes of the circles correspond to the numbers of parasites within each haplotype.</p

Principal coordinate analysis of <i>P</i>. <i>vivax</i> haplotypes from three provinces.

<p>Principal coordinate analysis of <i>P</i>. <i>vivax</i> haplotypes from three provinces.</p

Population genetic structure of <i>P</i>. <i>vivax</i> in three provinces (K = 2–5).

<p>The structure was plotted by using 10 (A) and (B) 4 MS markers (MS2, MS6, MS10 and MS12).</p

The mean number of alleles, the multiplicity of infection and the expected heterozygosity (<i>H</i>_<i>E</i>) per locus.

<p>The mean number of alleles, the multiplicity of infection and the expected heterozygosity (<i>H</i>_<i>E</i>) per locus.</p

Bottleneck analysis ^#.

<p>Bottleneck analysis <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005930#t004fn001" target="_blank">^#</a>.</p