Substantial population structure of Plasmodium vivax in Thailand facilitates identification of the sources of residual transmission.

Veerayuth Kittichai,Jetsumon Sattabongkot,Liwang Cui,Cristian Koepfli,Wang Nguitragool,Rhoel Ramos Dinglasan

doi:10.1371/journal.pntd.0005930

Abstract

BackgroundPlasmodium vivax 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.Methodology/ResultsA total of 127 P. vivax 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.Conclusion/SignificanceSignificant 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 P. vivax cases can be reliably determined by genotyping four microsatellite markers, which should be useful for monitoring parasite reintroduction after malaria elimination.

Highlights

The global incidence of malaria has been greatly reduced in recent years, Plasmodium vivax remains the most geographically widespread human malaria parasite [1]
This study presents an updated view of the P. vivax populations along the Thai-Myanmar and the Thai-Cambodian borders
Genotyping of parasite samples collected after intensified malaria control demonstrated that despite the decline in overall transmission intensity, the genetic diversity of the P. vivax parasites remained high

Summary

Introduction

The global incidence of malaria has been greatly reduced in recent years, Plasmodium vivax remains the most geographically widespread human malaria parasite [1]. Given the successful interruption of transmission in other parts of the country, information on diversity and genetic relationship of parasites from the remaining transmission hotspots can help target control programs to track the sources of remaining infections and to direct control programs towards remaining transmission hotspots. This is relevant for P. vivax, since the dormant liver hypnozoites can relapse months or even years after the initial infection in seemingly parasite-free migrants. Plasmodium vivax 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.

Methods

Results

Discussion

Conclusion