ASSESSMENT OF Plasmodium falciparum RESISTANCE TO PIPERAQUINE AND OTHER FRONTLINE ANTIMALARIALS IN KENYA USING GENOMIC ANALYSES AND GROWTH INHIBITION ASSAYS

Abstract

Dihydroartemisinin-piperaquine (DHA-PPQ) is an alternative first-line antimalarial to artemether- lumefantrine in Kenya. However, recent reports on emergence of PPQ resistance in Southeast Asia threaten its continued use in Kenya and Africa. In line with the policy on continued deployment of DHA-PPQ, it is imperative to monitor susceptibility of Kenyan parasites to PPQ and other frontline antimalarials in order to clarify its field expedience at this period of intensified deployment. Parasites isolates from samples collected between 2008 and 2021 from individuals with naturally acquired P. falciparum infections presenting with uncomplicated malaria were tested for in vitro susceptibility to piperaquine, dihydroartemisinin, lumefantrine, artemether, and chloroquine using the malaria SYBR Green I method. A subset of the 2019-2021 samples was further tested for ex vivo susceptibility to PPQ using piperaquine survival assay (PSA). Each isolate was also characterized for mutations associated with antimalarial resistance in Pfcrt, Pfmdr1, Pfpm2/3, Pfdhfr, and Pfdhps genes using real-time PCR and Agena MassARRAY platform. Associations between phenotype and genotype were also determined using the Kruskal-Wallis H- test and Mann-Whitney U test. The PPQ median IC50 interquartile range (IQR) remained stable during the study period, 32.70 (IQR 20.2-45.6) nM in 2008 and 27.30 (IQR 6.9-52.8) nM in 2021, (P=0.1615). The median ex vivo piperaquine survival rate (IQR) was 0 (0-5.27) %, at 95% CI. Five isolates had PSA survival rate of ≥10%, consistent with the range of PPQ resistant parasites, though they lacked polymorphisms in Pfmdr1 and Plasmepsin genes. Lumefantrine and artemether median IC50s rose significantly to 62.40 (IQR 26.9-100.8) nM, (P = 0.0201); 7.00 (IQR 2.4-13.4) nM, (P = 0.0021) in 2021from 26.30 (IQR 5.1-64.3) nM; 2.70 (IQR 1.3-10.4) nM in 2008, respectively. Conversely, chloroquine median IC50s decreased significantly to 10.30, (IQR 7.2- 20.9) nM in 2021 from 15.30 (IQR 7.6-30.4) nM in 2008, coinciding with a decline in prevalence of Pfcrt 76T allele over time from 39.3% to 0% (P = 0.0357). The proportions of piperaquine- resistant markers including Pfpm2/3 and Pfmdr1 did not vary significantly. However, a significant association was observed between PPQ IC50 and Pfcrt K76T allele (P=0.0026). Circulating Kenyan parasites have remained sensitive to PPQ and other antimalarials, though response to artemether and lumefantrine is declining. This study forms a baseline for continued surveillance of current antimalarials for timely detection of resistance.