A common DNA deletion altering the 3’UTR of mdr1 is associated with reduced mefloquine susceptibility in P. vivax parasites from Cambodian patients

Artemisinin-combination therapies (ACTs) are now recommended for the treatment of uncomplicated malaria caused by Plasmodium vivax , the parasite responsible for the majority of malaria infections outside of Africa. We analyzed the genome sequences of 206 P. vivax parasites collected from Cambodian malaria patients and showed that more than 80% of them carried a DNA deletion located immediately downstream of the multidrug resistance 1 gene ( mdr1 ). This 837 bp deletion overlapped with a different deletion present at low frequency in South American isolates, suggesting a functional role despite not altering the coding sequence of mdr1 . Using RNA sequencing, we showed that these deletions altered the transcripts expressed from mdr1 and resulted in mRNAs with different 3’ untranslated regions. In Cambodian isolates, the deletion was significantly associated with a higher expression of mdr1 and a lower ex vivo susceptibility to mefloquine. Finally, we genotyped 592 Cambodian isolates collected between 2014 and 2024 and showed that the mdr1 deletion increased in frequency in Cambodia since the introduction of mefloquine as ACT partner drug. Overall, these findings indicate that a common deletion of a non-coding sequence affects the transcription, stability, or translation of mdr1 in P. vivax parasites and could mediate reduced susceptibility to antimalarial drug(s) currently used for the treatment of uncomplicated vivax malaria.