Artemisinin resistance in Plasmodium falciparum

Abstract

We reported in The Lancet Infectious Diseases1Witkowski B Amaratunga C Khim N et al.Novel phenotypic assays for the detection of artemisinin-resistant Plasmodium falciparum malaria in Cambodia: in-vitro and ex-vivo drug-response studies.Lancet Infect Dis. 2013; 13: 1043-1049Summary Full Text Full Text PDF PubMed Scopus (361) Google Scholar that survival of Plasmodium falciparum differs significantly between fast-clearing and slow-clearing parasites isolated from patients with malaria treated with an artemisinin in western Cambodia (10·88% vs 0·23%, p=0·007). Of the 26 parasites tested, however, we found that four gave discordant results. Of the 13 fast-clearing parasites, three had high survival rates (5·30%, 19·32%, and 51·39%) but a resistant stage-dependent pattern (decrease in survival as parasites matured of 1·2%, 17·3%, and 50·2%, respectively). We postulated that these three parasites were indeed artemisinin-resistant, but that their clearance was fast because circulating parasites seen in blood films were predominantly older, drug-sensitive rings at the time the patients received artemisinin drugs. Of the 13 slow-clearing parasites, one had a paradoxically low survival (0·16%). We believe that this parasite was in fact artemisinin-sensitive, but that its clearance was slow because the patient had low levels of parasite-clearing immunity2Lopera-Mesa TM Doumbia S Chiang S et al.Plasmodium falciparum clearance rates in response to artesunate in Malian children with malaria: effect of acquired immunity.J Infect Dis. 2013; 207: 1655-1663Crossref PubMed Scopus (55) Google Scholar or a poor pharmacokinetics profile. We reported K13-propeller polymorphism as a new molecular marker for artemisinin-resistant P falciparum malaria,3Ariey F Witkowski B Amaratunga C et al.A molecular marker of artemisinin-resistant Plasmodium falciparum malaria.Nature. 2014; 505: 50-55Crossref PubMed Scopus (1227) Google Scholar and postulated that K13-propeller genotypes would definitively resolve the four discordant results. To test this possibility we genotyped all 26 parasites and found that the three parasites with discordantly high survival rates each carry a different mutant K13-propeller allele (Tyr493His, Cys580Tyr, and Arg539Thr), and that the parasite with a discordantly low survival rate carried a wild-type allele (figure). As expected, we also found that all the fast-clearing and slow-clearing parasites with concordant survival rates had wild-type or mutant alleles (Tyr493His and Cys580Tyr), respectively. These data suggest that parasite survival rates in the ring-stage survival assay are more relevant than parasite clearance half-lives for identifying artemisinin-resistant P falciparum, and further validate K13-propeller polymorphisms as a molecular marker of artemisinin resistance in vitro and in vivo. We declare no competing interests. Novel phenotypic assays for the detection of artemisinin-resistant Plasmodium falciparum malaria in Cambodia: in-vitro and ex-vivo drug-response studiesThe in-vitro RSA of 0–3 h ring-stage parasites provides a platform for the molecular characterisation of artemisinin resistance. The ex-vivo RSA can be easily implemented where surveillance for artemisinin resistance is needed. Full-Text PDF