As of December 2017, artemisinin resistance has been confirmed in 5 countries of the Greater Mekong Subregion (GMS): Cambodia, the Lao People’s Democratic Republic, Myanmar, Thailand and Viet Nam. In the large majority of sites, patients with artemisinin-resistant parasites still recover after treatment. However, along the Cambodia-Thailand border, P. falciparum has become resistant to almost all available antimalarial medicines. There is a real risk that multidrug resistance will soon emerge in other parts of the subregion as well. Artemisinin resistance has occurred as a consequence of several factors, including poor treatment practices, inadequate patient adherence to prescribed antimalarial regimens, and the widespread availability of oral artemisinin-based monotherapies and substandard forms of the drug.

The geographic scope of the problem could widen quickly, and have important public health consequences: the spread or independent emergence of artemisinin resistance in other parts of the world could pose a health security risk as no alternative antimalarial medicine is available at present with the same level of efficacy and tolerability as ACTs.

In late 2013, researchers identified molecular markers: mutations in the Kelch 13 (K13) propeller domain were shown to be associated with delayed parasite clearance in vitro and in vivo. The molecular marker could allow for a more precise mapping and monitoring of the geographical distribution of resistance. It could also enable a retrospective mapping of possible resistance in a large number of settings. WHO is working with researchers, national malaria programmes, and other partners – within and outside of the GMS– to map the presence of artemisinin resistance. More details are expected to be available by the end of 2014. Meanwhile, therapeutic efficacy studies will continue to remain a central tool for monitoring the efficacy of nationally recommended antimalarial
treatments in all countries.