Selection and Spread of Artemisinin-Resistant Alleles in Thailand Prior to the Global Artemisinin Resistance Containment Campaign

The recent emergence of artemisinin resistance in the Greater Mekong Subregion poses a major threat to the global effort to control malaria. Tracking the spread and evolution of artemisinin-resistant parasites is critical in aiding efforts to contain the spread of resistance. A total of 417 patient samples from the year 2007, collected during malaria surveillance studies across ten provinces in Thailand, were genotyped for the candidate Plasmodium falciparum molecular marker of artemisinin resistance K13. Parasite genotypes were examined for K13 propeller mutations associated with artemisinin resistance, signatures of positive selection, and for evidence of whether artemisinin-resistant alleles arose independently across Thailand. A total of seven K13 mutant alleles were found (N458Y, R539T, E556D, P574L, R575K, C580Y, S621F). Notably, the R575K and S621F mutations have previously not been reported in Thailand. The most prevalent artemisinin resistance-associated K13 mutation, C580Y, carried two distinct haplotype profiles that were separated based on geography, along the Thai-Cambodia and Thai-Myanmar borders. It appears these two haplotypes may have independent evolutionary origins. In summary, parasites with K13 propeller mutations associated with artemisinin resistance were widely present along the Thai-Cambodia and Thai-Myanmar borders prior to the implementation of the artemisinin resistance containment project in the region.近期，大湄公河次区域（Greater Mekong Subregion）出现的青蒿素（artemisinin）耐药性问题，对全球疟疾防控工作构成了严重威胁。追踪抗青蒿素疟原虫的传播与演化，对遏制耐药性扩散的相关工作至关重要。本研究共纳入2007年采集的417份患者样本：这些样本采自泰国10个省份的疟疾监测项目，针对候选的抗青蒿素恶性疟原虫（Plasmodium falciparum）分子标记K13完成了基因分型检测。研究对疟原虫基因型展开三项分析：一是检测与青蒿素耐药性相关的K13桨域突变，二是寻找正向选择信号，三是验证泰国境内的抗青蒿素等位基因是否为独立起源。最终共检出7种K13突变等位基因，分别为N458Y、R539T、E556D、P574L、R575K、C580Y及S621F。值得注意的是，R575K与S621F这两种突变此前从未在泰国境内被报道。最为常见的抗青蒿素相关K13突变C580Y，存在两种截然不同的单倍型（haplotype）图谱，二者依据地理分布分别对应泰国-柬埔寨边境与泰国-缅甸边境区域。分析显示，这两种单倍型可能拥有独立的演化起源。综上，在该区域启动青蒿素耐药性遏制项目之前，携带与青蒿素耐药性相关的K13桨域突变的疟原虫，已广泛分布于泰国-柬埔寨边境与泰国-缅甸边境沿线地区。