Artemisinin Partial Resistance Mutations in Zanzibar and Tanzania Suggest Regional Spread and African Origins, 2023.

Artemisinin partial resistance (ART-R), driven by Plasmodium falciparum K13 mutations, threatens malaria control. Zanzibar is vulnerable to ART-R spread but lacks recent molecular surveillance. We sequenced samples in Zanzibar and mainland Tanzania collected in 2022-2024. K13 mutations (P441L, A675V) were found in 2/1440 Zanzibar participants and 6/3762 (R561H, P441L) in mainland Tanzania. K13 mutations appear to be of African origin and spreading regionally based on whole genome sequencing data. Frequent parasite importation appears to maintain partner drug mutation frequencies similar to the mainland, where artemether-lumefantrine selects for mutations favoring artesunate-amodiaquine sensitivity. Ongoing molecular surveillance remains essential to track these patterns.