The PfK13 G533S mutation confers artemisinin partial resistance in multiple genetic backgrounds of .

Mutations in the Kelch 13 (PfK13) protein are the key determinant of artemisinin partial resistance. While more than 200 PfK13 mutations have been identified in global parasite populations, only 13 have been validated to confer or artemisinin partial resistance. In the western Greater Mekong Subregion, the prevalence of the PfK13 G533S mutation has significantly increased in recent years. Field isolates carrying the PfK13 G533S mutation showed slower parasite clearance and higher day-3 positivity rates after artemisinin treatment, while culture-adapted isolates displayed significantly elevated ring-stage survival rates. Here, the PfK13 G533S mutation was introduced using CRISPR/Cas9 into four parasite strains: Dd2, 3D7, GB4, and F09N25 (a recent culture-adapted field isolate from the China-Myanmar border area). Across all four genetic backgrounds, the PfK13 G533S mutation conferred ring-stage survival rates of 12%-23% with a minimal fitness cost, explaining its rising prevalence in the region. In contrast, the PfK13 G533A mutation, sporadically detected in world populations, did not increase ring-stage survival rates when engineered into the 3D7 and Dd2 strains. These findings validate the G533S mutation as a critical marker for artemisinin resistance surveillance and underscore the importance of monitoring its spread.