BACKGROUND: Plasmodium falciparum multidrug resistance transporter 1 (Pfmdr1) gene mutations are associated with altered response to artemisinin-based combination therapy (ACT), particularly the combinations containing the partner drugs lumefantrine and amodiaquine (i.e., artemether-lumefantrine [AL] and artesunate-amodiaquine [ASAQ]). Past studies of Pfmdr1 single nucleotide polymorphisms (SNPs) at codons 86, 184, and 1246 have shown different responses to AL and ASAQ. METHODS: To determine whether infection with parasites carrying specific Pfmdr1 SNPs leads to increased risk of recurrent parasitaemia (recrudescent or new infection), data from 3,915 samples from 16 therapeutic efficacy studies from 13 African countries between 2013 and 2019 were analysed. RESULTS: Patients treated with AL and infected with parasites carrying Pfmdr1 N86 were at greater risk of recurrent infection than those whose parasites carried 86Y. After treatment with ASAQ, individuals infected with parasites that carried Pfmdr1 86Y were more likely to experience a recurrent infection. CONCLUSIONS: These results support prior studies that suggested: (1) patients given AL and infected with parasites carrying N86 were more likely to experience a recurrent infection; (2) patients given ASAQ and infected with parasites carrying 86Y were more likely to experience a recurrent infection. These findings suggest that ACT and Pfmdr1 genotype may influence outcome after Plasmodium falciparum infection.

BACKGROUND: Anti-malarial drug resistance remains a major threat to global malaria control efforts. In Africa, Plasmodium falciparum remains susceptible to artemisinin-based combination therapy (ACT), but the emergence of resistant parasites in multiple countries in Southeast Asia and concerns over emergence and/or spread of resistant parasites in Africa warrants continuous monitoring. The World Health Organization recommends that surveillance for molecular markers of resistance be included within therapeutic efficacy studies (TES). The current study assessed molecular markers associated with resistance to Artemether-lumefantrine (AL) and Dihydroartemisinin-piperaquine (DP) from samples collected from children aged 6-59 months enrolled in a TES conducted in Siaya County, western Kenya from 2016 to 2017. METHODS: Three hundred and twenty-three samples collected pre-treatment (day-0) and 110 samples collected at the day of recurrent parasitaemia (up to day 42) were tested for the presence of drug resistance markers in the Pfk13 propeller domain, and the Pfmdr1 and Pfcrt genes by Sanger sequencing. Additionally, the Pfpm2 gene copy number was assessed by real-time polymerase chain reaction. RESULTS: No mutations previously associated with artemisinin resistance were detected in the Pfk13 propeller region. However, other non-synonymous mutations in the Pfk13 propeller region were detected. The most common mutation found on day-0 and at day of recurrence in the Pfmdr1 multidrug resistance marker was at codon 184F. Very few mutations were found in the Pfcrt marker (< 5%). Within the DP arm, all recrudescent cases (8 sample pairs) that were tested for Pfpm2 gene copy number had a single gene copy. None of the associations between observed mutations and treatment outcomes were statistically significant. CONCLUSION: The results indicate absence of Pfk13 mutations associated with parasite resistance to artemisinin in this area and a very high proportion of wild-type parasites for Pfcrt. Although the frequency of Pfmdr1 184F mutations was high in these samples, the association with treatment failure did not reach statistical significance. As the spread of artemisinin-resistant parasites remains a possibility, continued monitoring for molecular markers of ACT resistance is needed to complement clinical data to inform treatment policy in Kenya and other malaria-endemic regions.