Gametocyte production and infectivity among Ugandan malaria patients infected with P. falciparum with partial resistance to artemisinins

Background: Partial resistance to artemisinins (ART-R) has emerged in East Africa, associated with mutations in the Plasmodium falciparum kelch13 gene. It is currently unclear whether ART-R has implications for gametocyte production or for onward transmission to mosquitoes. Methods: In a cohort of uncomplicated malaria patients attending Kalongo Hospital in northern Uganda, we quantified carriage of PfKelch13 mutant parasites by conventional sequencing and droplet digital PCR (ddPCR) for the C469Y and A675V mutations. Prevalence and density of gametocytes and ring-stage parasites were assessed by microscopy and quantitative reverse-transcriptase PCR (qRT-PCR). Lumefantrine concentrations, indicative of prior malaria treatment, were determined by ultra-high performance liquid chromatography-tandem mass spectrometry. Transmission potential of wild-type and PfKelch13 mutant parasites was assessed by mosquito feeding assays and complemented with molecular characterization of parasites in wild-caught mosquitoes from household resting catches. Findings: We enrolled 235 patients with symptomatic P. falciparum infection; PfKelch13 C469Y or A675V mutations were detected in 35.8% (78/218) of infections by sequencing and 59.1% (136/230) by ddPCR. Gametocyte carriage was 24.0% (56/233) by microscopy and 56.6% (133/235) by qRT-PCR and not associated with the abundance of PfKelch13 mutant parasites by ddPCR (p=0.603). Among a total of 227 mosquito feeds with patient whole blood, 1.4% (120/8745) of mosquitoes became infected. Mosquito infection rates were positively associated with gametocyte density ({beta} = 0.39, 95% CI = 0.23-0.59, p < 0.001) without an observed interaction with the abundance of PfKelch13 mutant parasites (p = 0.452). PfKelch13 C469Y or A675V mutations were detected in 40.1% (21/52) of malaria-infected bloodmeals of field-caught mosquitoes and in 28.0% (7/25) of sporozoite-positive mosquitoes. Interpretation: We conclude that pfkelch13 mutations are very common in patients in northern Uganda with uncomplicated malaria, mostly in multiclonal infections. We observed no evidence that ART-R affected gametocyte production or transmission to mosquitoes. Funding: Dutch Research Council (NWO)