K13-Propeller Polymorphisms in Plasmodium falciparum Parasites From Sub-Saharan Africa

The emergence of Plasmodium falciparum parasites resistant to artemisinin and its derivatives, recently documented in Southeast Asia [1–3], threatens to reverse recent gains made in malaria control worldwide and presents a major roadblock to eliminating malaria. Although in vivo efficacy studies are widely used for tracking artemisinin resistance in Southeast Asia, in Africa and other malaria-endemic regions, there is a need for concerted efforts to develop in vitro or ex vivo assays and to identify genetic markers of artemisinin resistance. Toward this effort, Witkowski et al recently described novel phenotypic assay for detection of artemisinin-resistant P. falciparum parasites, the ring-stage survival assay (RSA0–3 hours) [4]. Furthermore, evaluation of the P. falciparum genome for regions of recent strong evolutionary selection and genome-wide association studies revealed regions on chromosomes 10 and 13 that are potential loci involved in artemisinin resistance [3, 5]. In a recent study, Ariey et al showed that RSA0–3 hours survival rates and slow parasite clearance were associated with single-nucleotide polymorphisms (SNPs) in the PF3D7_1343700 kelch propeller domain on chromosome 13 (K13-propeller) [6]. These authors demonstrated that the mutant alleles Y493H, R539T, I543T, and C580Y within the kelch repeat motif of the C-terminal K13-propeller domain conferred significantly higher RSA0–3 hours survival rates. Further analysis of geographic diversity of K13-propoller polymorphisms across 10 provinces in Cambodia revealed a large number of mutations, with the C580Y allele accounting for 85% of all mutations. The majority (74%) of the parasites harbored a single nonsynonymous mutation in the K13-propeller with geographic disparity in their distribution; K13-propeller mutations were more prevalent in provinces with documented artemisinin resistance. For K13-propeller polymorphisms to be used universally as a tool for tracking artemisinin resistance and translated into a public health tool, global validation of these markers must be conducted. Toward this effort, we sought to assess the prevalence of polymorphisms in the K13-propeller gene in samples collected across sub-Saharan Africa in regions where artemisinin-combination therapies (ACTs) are routinely used for treatment of malaria. This study provides baseline prevalence of K13-propeller polymorphism in sub-Saharan Africa.