Dynamics of Plasmodium vivax populations in border areas of the Greater Mekong sub-region during malaria elimination

Abstract

Background: Countries within the Greater Mekong Sub-region (GMS) of Southeast Asia have committed to eliminating malaria by 2030. Although the malaria situation has greatly improved, malaria transmission remains at international border regions. In some areas, Plasmodium vivax has become the predominant parasite. To gain a better understanding of transmission dynamics, knowledge on the changes of P. vivax populations after the scale-up of control interventions will guide more effective targeted control efforts. Methods:This study investigated genetic diversity and population structures in 206 P. vivax clinical samples collected at two time points in two international border areas: the China-Myanmar border (CMB) (n = 50 in 2004 and n = 52 in 2016) and Thailand-Myanmar border (TMB) (n = 50 in 2012 and n = 54 in 2015). Parasites were genotyped using 10 microsatellite markers.Results: Despite intensified control efforts, genetic diversity remained high (H E = 0.66-0.86) and was not significantly different among the four populations (P > 0.05). Specifically, H E slightly decreased from 0.76 in 2004 to 0.66 in 2016 at the CMB and increased from 0.80 in 2012 to 0.86 in 2015 at the TMB. The proportions of polyclonal infections varied significantly among the four populations (P < 0.05), and showed substantial decreases from 48.0% in 2004 to 23.7 at the CMB and from 40.0% in 2012 to 30.7% in 2015 at the TMB, with corresponding decreases in the multiplicity of infection. Consistent with the continuous decline of malaria incidence in the GMS over time, there were also increases in multilocus linkage disequilibrium, suggesting more fragmented and increasingly inbred parasite populations. There were considerable genetic differentiation and sub-division among the four tested populations. Temporal genetic differentiation was observed at each site (F ST = 0.081 at the CMB and F ST = 0.133 at the TMB). Various degrees of clustering were evident between the older parasite samples collected in 2004 at the CMB and the 2016 CMB and 2012 TMB populations, suggesting some of these parasites had shared ancestry. In contrast, the 2015 TMB population was genetically distinctive, which may reflect a process of population replacement. Whereas the effective population size © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article' s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article' (N e ) at the CMB showed a decrease from 4979 in 2004 to 3052 in 2016 with the infinite allele model, the N e at the TMB experienced an increase from 6289 to 10,259. Conclusions:With enhanced contr...

A retrospective analysis of malaria epidemiological characteristics in Yingjiang County on the China–Myanmar border

“…The proportion of vivax malaria cases in Yingjiang County increased from 2013 to 2019 and no falciparum malaria cases were reported in 2019, indicating that P. vivax was the predominant species on the Myanmar side and the rate of P. falciparum infection in Myanmar was very low because more than 95% of the imported cases were from Myanmar. This change was similar to that in other countries in the Greater Mekong sub-region 28 , 29 . The epidemiology of vivax malaria in this region is highly heterogeneous and P. vivax has become a major challenge to malaria elimination in this region 30 , 31 .…”

Genetic Diversity and Natural Selection of Plasmodium vivax Duffy Binding Protein-II From China-Myanmar Border of Yunnan Province, China

“…Previous studies have found PvDBP-II under a strong selection. The high rates of non-synonymous to synonymous mutations reflected a positive selection promoting greater polymorphism, which may allow the evasion of host immune selection independently of the geographical distribution ( Li et al, 2020 ). In this study, the rate of non-synonymous to synonymous mutations indicated that the PvDBP-II of CMB isolates was also under positive selection.…”

“…P. vivax has become the most dominant parasite in the GMS region. Better understanding of transmission dynamics and population structure is essential to develop appropriate interventions for malaria elimination ( Li et al, 2020 ). Myanmar border malaria is a major source of disease transmission and infection in the CMB in Yunnan Province.…”

Temporal Changes in the Genetic Diversity of Plasmodium vivax Merozoite Surface Protein-1 in Myanmar

“…Although malaria incidences have significantly declined in the central part of Myanmar in the last decade, migration from endemic areas or international border areas such as the Myanmar-China and Myanmar-Thailand borders has been increasing in recent years due to political instability and job recruiting. Large P. vivax reservoirs, including asymptomatic individuals, still maintain genetic diversity and transmission in the border areas with considerable spatial and temporal differentiations [ 6 , 26 , 27 ]. Further studies on the influx of P. vivax from other endemic areas or boarder areas and its contribution to the population diversity of P. vivax in Mandalay areas are also necessary to understand the causes of the increase in genetic diversity of the P. vivax population in the studied areas, and to provide guidelines for effective control measures.…”