Geographic structure of Plasmodium vivax: microsatellite analysis of parasite populations from Sri Lanka, Myanmar, and Ethiopia

Abstract

Genetic diversity and population structure of Plasmodium vivax parasites can predict the origin and spread of novel variants within a population enabling population specific malaria control measures. We analyzed the genetic diversity and population structure of 425 P. vivax isolates from Sri Lanka, Myanmar, and Ethiopia using 12 trinucleotide and tetranucleotide microsatellite markers. All three parasite populations were highly polymorphic with 3-44 alleles per locus. Approximately 65% were multiple-clone infections. Mean genetic diversity (H(E)) was 0.7517 in Ethiopia, 0.8450 in Myanmar, and 0.8610 in Sri Lanka. Significant linkage disequilibrium was maintained. Population structure showed two clusters (Asian and African) according to geography and ancestry. Strong clustering of outbreak isolates from Sri Lanka and Ethiopia was observed. Predictive power of ancestry using two-thirds of the isolates as a model identified 78.2% of isolates accurately as being African or Asian. Microsatellite analysis is a useful tool for mapping short-term outbreaks of malaria and for predicting ancestry.

Figure 1.

A, Population structure of Plasmodium vivax plotted in a single line according to geographic origin (Asian or African) inferred from microsatellite typing of 425 isolates at K = 2. Isolates are numbered as 1–140 from Sri Lanka, 141–307 from Myanmar, and 308–425 from Ethiopia. B, Population structure of P. vivax plotted in multiple lines according to geographic origin (Asian or African) inferred from microsatellite typing of 425 isolates at K = 2. Isolates 1–140 were collected in Sri Lanka: 1–21 in Trincomalee (2007); 22–41 in Trincomalee (2005); 42–61 in Anuradhapura (2004); 62–77 in Polonnaruwa (2004); 78–81 in Polonnaruwa (2005); 82–88 in Vavuniya (2005); 89 in Mannar (2004); 90–92 in Mannar (2005); 93–109 in Batticaloa (2005); 100 in Ampara (2004); 111–114 in Ampara (2005); 115–116 in Monaragala (2005); 117 in Monaragala (2006); 118–120 in Kurunegala (2005); 121–137 in Kurunegala (2006); 138 in Colombo (2005); 139 in Colombo (2008); 140 in Colombo (2003). Isolates 141–307 were collected in Myanmar: 141–236 in Kayin State (2007); 237–292 in Kachin State (2007); 293–307 in Rakhine State (2007). Isolates 308–425 were collected in Ethiopia: 308–366 in Assendabo (2006); 367–418 in Assendabo (2007); 419–425 in Assendabo (2008). This figure appears in color at www.ajtmh.org.

Figure 2.

Population structure of Plasmodium vivax plotted in a single line according to geographic location inferred from microsatellite typing of 425 isolates at K = 3. Isolates 1–140 were collected in Sri Lanka; 141–307 in Myanmar; and 308–425 in Ethiopia. This figure appears in color at www.ajtmh.org.

Figure 3.

Population structure of Plasmodium vivax according to ancestry inferred from microsatellite typing of 425 isolates at K = 2 (single and multiple line plots). Predominant ancestry (> 70%) for Asian and African isolates in each cluster was as follows: red = 62.7% (n = 74) African and 12.7% (n = 39) Asian; green = 48.8% (n = 150) Asian and 5.9% (n = 7) African. This figure appears in color at www.ajtmh.org.