Characterization of polymorphisms in Plasmodium falciparum artemisinin resistance marker kelch13 in asymptomatic infections in a rural area of Cameroon

Abstract

BackgroundThe genetic variability of the artemisinin resistance (AR) molecular marker kelch13 has been extensively investigated in Plasmodium falciparum malaria parasites from symptomatic infections in South East (SE) Asia where AR is highly prevalent, as well as in Africa where evidence of AR has emerged only recently. However, molecular surveillance and risk of transmission of AR also require monitoring asymptomatic infection. Here, molecular analyses were used to investigate polymorphisms in kelch13 and their potential for transmission in asymptomatic adults in Bolifamba, Cameroon in Central Africa.\n\nMethodsUsing polymerase chain reaction (PCR), we amplified and sequenced the full length of kelch13 from P. falciparum infections detected in the blood of 33 asymptomatic adults (age: 18-55 years-old) collected in a cross-sectional study from July 2008 to October 2009. Risk of increased transmission was assessed by quantifying gametocytes by qPCR. Quantitative ELISA was used to detect plasma levels of PfHRP2 to establish total parasite burdens associated with asymptomatic infection.\n\nResultsOut of 33 isolates tested, 14 (42.4%) presented at least a single nucleotide polymorphism (SNP) in kelch13. Five non-synonymous SNPs were detected (K189T/N, N217H, R393K and E433K). None were located in the beta-propeller domain, where AR mutations have been detected in both SE Asian and, more recently, African parasites. K189T/N and N217H have been previously reported in African strains, but R393K and E433K are new polymorphisms. Gametocytes were detected in 24.2% of infections, without a significant association with detected Kelch13 polymorphisms. Notably, polymorphisms detected in kelch13 were associated with a significant increase of PfHRP2 plasma levels.\n\nConclusionsThis study provides the baseline prevalence of kelch13 polymorphisms in asymptomatic infection for molecular surveillance in tracking AR, and suggests the need for additional studies to explore the association of kelch13 polymorphisms with P. falciparum burden independent of AR, in this region of Cameroon.