Limited geographical origin and global spread of sulfadoxine-resistant dhps alleles in Plasmodium falciparum populations

Abstract

Background: Plasmodium falciparum malaria resistant to chloroquine and pyrimethamine originated in limited foci and migrated to Africa. It remains unresolved whether P. falciparum resistance to sulfadoxine, which is conferred by mutations in dihydropteroate synthase (DHPS), evolved following a similar pattern.

Methods: The dhps locus of 893 P. falciparum isolates from 12 countries in Asia, the Pacific Islands, Africa, and South America was sequenced. Haplotypes of 6 microsatellite loci flanking the dhps locus were determined to define the genetic relationships among sulfadoxine-resistant lineages.

Results: Six distinct sulfadoxine-resistant lineages were identified. Highly resistant lineages appear to have originated only in Southeast Asia and South America. Two resistant lineages found throughout Southeast Asia have been introduced to East Africa, where they appear to have spread.

Conclusions: The infrequent selection of parasites highly resistant to sulfadoxine and the subsequent migration of resistant lineages from Asia to Africa are similar to the patterns observed in chloroquine and pyrimethamine resistance. These findings strongly suggest that the global migration of resistant parasites has played a decisive role in the establishment of drug-resistant P. falciparum parasites, and that similar patterns may be anticipated for the spread of artemisinin resistance.

Figure 1.

Geographical distribution of dhps alleles in 893 Plasmodium falciparum isolates from 12 countries. Capital letters next to the shaded boxes denote amino acid residues at positions 436, 437, 540, 581, and 613, with mutations identified in red. Other mutations (underlined) include alleles of CAKAA, FAKAA, HAKAA, SGKAG, AGKGA, and AGEAE with frequencies of <0.2%.

Figure 2.

Bayesian population structure analysis (A) and median-joining network diagram (B) indicating the presence of 6 lineages of sulfadoxine-resistant Plasmodium falciparum. A, Plot from highest log likelihood STRUCTURE run at K = 6. Individual isolates (n = 356) are grouped by collection site. Each individual is represented by a vertical bar displaying proportion of membership to each of 6 clusters: red (Southeast Asia and East Africa [SEA/EAFR-1], orange (SEA/EAFR-2), blue (Southeast Asia and Pacific Islands [SEA/PAC]), light green (Republic of the Congo [CON]), green (Ghana [GHA]), and purple (Brazil [BRA]). B, Haplotype network of 343 individuals comprising 99 haplotypes (Supplementary Figure 1), based on allelic variations in the 6 microsatellite loci flanking the dhps locus. Each individual was counted as belonging to its major cluster. Individuals not assigned to any clusters by Bayesian population structure analysis were excluded from this analysis (n = 13). The size of each circle corresponds to the number of individuals sharing that haplotype, and the length of an edge is proportional to the number of genetic changes between the 2 haplotypes it connects.

Figure 3.

Geographical distribution of 6 major sulfadoxine-resistant dhps lineages of Plasmodium falciparum. Haplotypes not assigned to any 1 cluster (n = 13) are designated “unassigned” lineage (UA). Abbreviations: SEA/EAFR, Southeast Asia and East Africa; SEA/PAC, Southeast Asia and Pacific Islands; CON, Republic of the Congo; GHA, Ghana; BRA, Brazil.