Plasmodium falciparum K13 expression associated with parasite clearance during artemisinin-based combination therapy.

Background Delayed parasite clearance and, consequently, reduced efficacy of artemisinin-based combination therapies have been linked with Plasmodium falciparum K13 gene SNPs in Southeast Asia. In Africa, significantly prolonged clearance has not yet been observed and the presently restricted variation in parasite clearance cannot be explained by K13 polymorphisms. Objectives Our aim was to study the in vivo pfK13 transcriptional response in patients treated with artemether-lumefantrine and explore whether the pfk13 transcripts can explain the patients' parasite clearance outcomes. Patients and methods A total of 47 Tanzanian children with microscopically confirmed uncomplicated P. falciparum malaria were hospitalized and received artemether-lumefantrine treatment (clinical trial ID: NCT00336375). RNA was extracted from venous blood samples collected before treatment initiation and at five more timepoints after treatment. cDNA was synthesized and pfk13 transcripts measured by real-time PCR. Results A wide range of pfk13 transcript variation was observed throughout all timepoints after artemether-lumefantrine treatment. Taking parasite clearance data together with the pfk13 transcripts profile, we observed a negative correlation inferring that pfk13 down-regulation is associated with longer parasite clearance time. Conclusions The findings suggest that a reduced PfK13 transcriptional response may represent a first step towards artemisinin tolerance/resistance.