Prevalence of K13-propeller polymorphisms in Plasmodium falciparum from China-Myanmar border in 2007-2012

Abstract

Background: The recent emergence and spread of artemisinin resistance in the Greater Mekong Subregion poses a great threat to malaria control and elimination. A K13-propeller gene (K13), PF3D7_1343700, has been associated lately with artemisinin resistance both in vitro and in vivo. This study aimed to investigate the K13 polymorphisms in Plasmodium falciparum parasites from the China-Myanmar border area where artemisinin use has the longest history.

Methods: A total of 180 archived P. falciparum isolates containing 191 parasite clones, mainly collected in 2007-2012 from the China-Myanmar area, were used to obtain the full-length K13 gene sequences.

Results: Seventeen point mutations were identified in 46.1% (88/191) parasite clones, of which seven were new. The F446I mutation predominated in 27.2% of the parasite clones. The C580Y mutation that is correlated with artemisinin resistance was detected at a low frequency of 1.6%. Collectively, 43.1% of the parasite clones contained point mutations in the kelch domain of the K13 gene. Moreover, there was a trend of increase in the frequency of parasites carrying kelch domain mutations through the years of sample collection. In addition, a microsatellite variation in the N-terminus of the K13 protein was found to have reached a high frequency (69.1%).

Conclusions: This study documented the presence of mutations in the K13 gene in parasite populations from the China-Myanmar border. Mutations present in the kelch domain have become prevalent (>40%). A predominant mutation F446I and a prevalent microsatellite variation in the N-terminus were identified, but their importance in artemisinin resistance remains to be elucidated.

Figure 1

Prevalence of K13 mutations in parasites collected from the China-Myanmar border area in 2007–2012.

Figure 2

Distribution of the mutations in the predicted 3D model of the K13 propeller domain. The predicted structure of the propeller domain forms six propeller blades that contain predominantly strands. The locations of the various mutations are indicated by spheres, where red colour represents new mutations, orange for previous reported mutations, and pink for mutations correlated with ART resistance reported by Ariey et al. The relative frequencies of the mutations are reflected by the size of the spheres.

Figure 3

Frequencies of K13 mutations in 2007 to 2012. Significant increase in frequencies of mutations in the kelch domain in 2009 was noted.