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

Artemisinin partial resistance, driven by Plasmodium falciparum K13 mutations, threatens malaria control. Zanzibar is vulnerable to artemisinin partial resistance spread but lacks recent molecular surveillance. We sequenced samples in Zanzibar and mainland Tanzania collected from 2022 to 2024. K13 mutations were found in 2 of 1440 participants (P441L, A675V) in Zanzibar and 6 of 3762 (R561H, P441L) in mainland Tanzania. Based on whole genome sequencing data, K13 mutations appear to be of African origin with regional spread. 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.