Distinctive origin of artemisinin-resistant Plasmodium falciparum on the China-Myanmar border

Artemisinin (ART) is a novel antimalarial drug discovered in China that is quick, effective, and has few adverse side-effects1,2. The World Health Organization (WHO) has recommended ART-based combination therapies (ACT) as first-line drugs for the treatment of Plasmodium falciparum malaria in all malaria endemic countries3. This has contributed to the recent significant decline in the global malaria burden4. Resistance to ART in P. falciparum is characterized by slow parasite clearance in patients receiving ART or an ACT5. ART resistance was first detected along the Thai-Cambodian border and has been detected across mainland Southeast Asia5,6,7,8,9,10. The continued spread of ART resistance will threaten malaria control programs globally. Therefore, the WHO has established a Global Plan for Artemisinin Resistance Containment (GPARC) to halt the spread of the resistance11. To this end, it is important to identify new areas where ART resistance is prevalent in order to implement containment intervention. ART and its derivate drugs were discovered in China and have been widely used there for the past 30 years1,2. Nevertheless, little is known about the patterns of emergence and distribution of ART resistance in China, particularly on the southern border. Understanding whether ART resistance has spread to China, or independently emerged in China, is thus, of great interest. In attempts to contain the ART resistance, the prompt and effective detection and monitoring of resistant parasites is a huge challenge. However, significant progress has recently been made in this respect. First, a novel in vitro method has been established that can distinguish culture-adapted parasites from patients with slow-clearing or fast-clearing infections (based on a ring stage survival assay of 0 to 3 h ring stage parasites; ‘RSA0–3h’). The survival rates from RSA0–3h are strongly correlated with in vivo parasite clearance rates12. Second, the propeller domain of the K13 gene of P. falciparum has been identified as a molecular marker for the detection and monitoring of ART-resistant parasites. Mutations in this region of the K13 gene are associated with slow parasite clearance rates in vivo and high parasite survival rates in vitro13. A recent study showed that mutations in the propeller domain of the K13 gene could identify a parasite clearance half-life of >5 hours with 91.8% sensitivity and 88.4% specificity10. The RSA0–3h method and the K13 marker offer several advantages over in vivo measurement. of parasite clearance rates as they minimize the influence of confounding factors, including variation in host immunity, drug dosage, and drug absorption and metabolism12. Thus, both assays should provide the effective and prompt monitoring of P. falciparum isolates for their susceptibility to ART. In addition, recent studies identified several genetic markers that can distinguish the K13 mutant alleles based on their geographic locations14,15,16. Therefore, in this study we use these two assays to investigate if the ART-resistant malaria parasites emerged in China and its relevant border districts, and use additional genetic markers to trace the origins and evolution of the K13 mutant alleles.