Discordant Patterns of Genetic Variation at Two Chloroquine Resistance Loci in Worldwide Populations of the Malaria Parasite Plasmodium falciparum

Abstract

Mutations in the chloroquine resistance (CQR) transporter gene of Plasmodium falciparum (Pfcrt; chromosome 7) play a key role in CQR, while mutations in the multidrug resistance gene (Pfmdr1; chromosome 5) play a significant role in the parasite's resistance to a variety of antimalarials and also modulate CQR. To compare patterns of genetic variation at Pfcrt and Pfmdr1 loci, we investigated 460 blood samples from P. falciparuminfected patients from four Asian, three African, and three South American countries, analyzing microsatellite (MS) loci flanking Pfcrt (five loci [ϳ40 kb]) and Pfmdr1 (either two loci [ϳ5 kb] or four loci [ϳ10 kb]). CQR Pfmdr1 allele-associated MS haplotypes showed considerably higher genetic diversity and higher levels of subdivision than CQR Pfcrt allele-associated MS haplotypes in both Asian and African parasite populations. However, both Pfcrt and Pfmdr1 MS haplotypes showed similar levels of low diversity in South American parasite populations. Median-joining network analyses showed that the Pfcrt MS haplotypes correlated well with geography and CQR Pfcrt alleles, whereas there was no distinct Pfmdr1 MS haplotype that correlated with geography and/or CQR Pfmdr1 alleles. Furthermore, multiple independent origins of CQR Pfmdr1 alleles in Asia and Africa were inferred. These results suggest that variation at Pfcrt and Pfmdr1 loci in both Asian and African parasite populations is generated and/or maintained via substantially different mechanisms. Since Pfmdr1 mutations may be associated with resistance to artemisinin combination therapies that are replacing CQ, particularly in Africa, it is important to determine if, and how, the genetic characteristics of this locus change over time.

Geographic patterns of Plasmodium falciparum drug resistance distinguished by differential responses to amodiaquine and chloroquine

“…Except for a recent report of a single sample from Brazil containing the wild-type CQ-sensitive haplotype CVMNK (55), a significant return of CQ-sensitive parasites has not yet occurred among the MDAQ-resistant populations of SVMNT parasites in South America or in other regions where SVMNT is present and CQ has been either withdrawn or is no longer recommended (56). Consistent with these observations, Mehlotra et al (57) have found that variation in the pfcrt and pfmdr1 loci of Asian and African parasites populations is maintained by substantially different mechanisms than in South American populations where the haplotypes of pfcrt and pfmdr1 both exhibit relatively low levels of diversity. We also note the recent observation of increasingly prevalent SVMNT parasites in Tanzania where AQ pressure has presumably facilitated their spread (51,52).…”

Different Patterns of pfcrt and pfmdr1 Polymorphisms in P. falciparum Isolates from Nigeria and Brazil: The Potential Role of Antimalarial Drug Selection Pressure

“…8,21 Evidence of emergence and spread of chloroquine-resistant parasites with CVIET haplotypes from South East Asia to Africa have been documented. 8,21,22 Our single nucleotide polymorphisms findings in isolates from Brazil and Nigeria provide additional evidence supporting the association of SVMNT and CVIET haplotypes respectively with P. falciparum isolates of South American and African origin. However, recent studies from Africa, notably in Tanzania, 3 Angola, 17 and Ghana 22 have reported the presence of SVMNT pfcrt haplotype in parasites from these various areas.…”

“…8,21,22 Our single nucleotide polymorphisms findings in isolates from Brazil and Nigeria provide additional evidence supporting the association of SVMNT and CVIET haplotypes respectively with P. falciparum isolates of South American and African origin. However, recent studies from Africa, notably in Tanzania, 3 Angola, 17 and Ghana 22 have reported the presence of SVMNT pfcrt haplotype in parasites from these various areas. Although it has been proposed that human migration and the strong commercial relationship between Brazil and Angola could have allowed for the import of the SVMNT haplotype from Brazil to Angola, 17 the same haplotype was found in parasites from Tanzania, 3 a country without strong commercial relationship with South America.…”

Polymorphic patterns of pfcrt and pfmdr1 in Plasmodium falciparum isolates along the Thai-Myanmar border

“…Early detection of occurrence and spreading of antimalarial drug resistance would be greatly enhanced by the application of valid antimalarial resistance molecular markers. Among the candidate genes investigated to date, pfcrt mutation is widely acceptable as a reliable marker of chloroquine resistance, while pfmdr1 wild type including number of gene copies strong correlate to mefloquine and artesunate resistance in P. falciparum [15][16][17] . Despite the fact that chloroquine was withdrawn from treatment of falciparum malaria in Thailand for many decades, pfcrt mutation at least at the codon 76 was conserved in all P. falciparum isolates.…”