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

Abstract

Chloroquine (CQ) resistance (CQR) in Plasmodium falciparum originated from at least six foci in South America, Asia, and Oceania. Malaria parasites from these locations exhibit contrasting resistance phenotypes that are distinguished by point mutations and microsatellite polymorphisms in and near the CQR transporter gene, pfcrt, and the multidrug resistance transporter gene, pfmdr1. Amodiaquine (AQ), a 4-aminoquinoline related to CQ, is recommended and often used successfully against CQ-resistant P. falciparum in Africa, but it is largely ineffective across large regions of South America. The relationship of different pfcrt and pfmdr1 combinations to these drug-resistant phenotypes has been unclear. In two P. falciparum genetic crosses, particular pfcrt and pfmdr1 alleles from South America interact to yield greater levels of resistance to monodesethylamodiaquine (MDAQ; the active metabolite of AQ) than to CQ, whereas a pfcrt allele from Southeast Asia and Africa is linked to greater CQ than MDAQ resistance with all partner pfmdr1 alleles. These results, together with (i) available haplotype data from other parasites; (ii) evidence for an emerging focus of AQ resistance in Tanzania; and (iii) the persistence of 4-aminoquinoline-resistant parasites in South America, where CQ and AQ use is largely discontinued, suggest that different histories of drug use on the two continents have driven the selection of distinct suites of pfcrt and pfmdr1 mutations. Increasing use of AQ in Africa poses the threat of a selective sweep of highly AQ-resistant, CQ-resistant parasites with pfcrt and pfmdr1 mutations that are as advantaged and persistent as in South America.

Adaptive evolution of malaria parasites in French Guiana: Reversal of chloroquine resistance by acquisition of a mutation in pfcrt

“…1) has created a complex selection landscape operating on the pfcrt gene, which is known to impact the efficacy of multiple antimalarials (20,26). Our drug profiling data showed a significant loss of mdAQ resistance in field isolates harboring the PfCRT C350R mutation, consistent with earlier reports that highlighted the close correlation between CQ and mdAQ responses of PfCRT SVMNT parasites from South America (14). Our observation that mutant C350R isolates were nominally less susceptible to DHA, however, should be interpreted with caution, notably because in vitro artemisinin susceptibilities, as measured using IC 50 values, do not correlate with the clinical phenotype of delayed parasite clearance rates in southeast Asia (27,28).…”

“…Such a difference between South America and other endemic regions in response to CQ withdrawal is generally attributed to other amino acid changes in PfCRT and PfMDR1 (both present on the parasite digestive vacuole membrane), which accompany the PfCRT K76T substitution. Specifically, the SVMNT haplotype of South American parasites at PfCRT amino acids 72-76 has been found to be less deleterious than the CVIET haplotype present elsewhere (14,15). Another explanation for the virtual fixation of CQR alleles in South American parasites is that CQ continues to be used to treat P. vivax infections and therefore, may exert a residual pressure.…”

Distribution Pattern of Plasmodium falciparum Chloroquine Transporter (pfcrt) Gene Haplotypes in Sri Lanka 1996–2006

“…6 Recent studies also suggest that CVIET mutants may incur a higher fitness cost than SVMNT mutants, which was indicated by the recovery of CQ-sensitive strains after the cessation of drug pressure in regions where the CVIET haplotype was prevalent but not in regions of high SVMNT prevalence. 11 This finding may be informative in planning future treatment policies, because artemisinin-based combination therapy (ACT) has replaced CQ as Figure 2. High-resolution melt curves.…”

“…8,9 Furthermore, the haplotypes observed in codons 72-76 have been associated with different fitness costs, coresistance to amodiaquine, and geographic origins. [10][11][12] A previous study has investigated these markers in Sri Lanka, finding that, among 76 samples collected from patients in the Mannar district of Northern Province in 2002 and 2004, 76.3% had the T76 mutation. 7 However, no published studies from outside the Mannar district have yet measured the change in haplotype frequencies in Sri Lanka over time.…”

Quantitative assessment of Plasmodium falciparum sexual development reveals potent transmission-blocking activity by methylene blue

“…Such a mode of action would be similar to 4-aminoquinolines such as chloroquine or amodiaquine. However, mechanisms of resistance to those drugs, mediated by the multidrug transporters PfCRT and PfMDR1 (40,41), do not impart cross-resistance to MB (36,42), and a separate mode of action must underlie MB activity against mature gametocytes in which hemoglobin degradation no longer occurs. Given that these forms are often refractory to antimalarial drugs, our data suggest that MB or a derivative thereof could be a highly effective transmission-blocking adjunct to curative antimalarial combinations.…”