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Artemisinin resistance was recently shown to have spread or emerged on the Thailand/Myanmar border. Evidence is accumulating that the parasite clearance time after artemisinin-based combination therapy (ACT) is increasing in settings in Asia and Africa. It is currently unknown if an extended parasite clearance time after ACTs has consequences for the individual patient or confers a higher malaria transmission potential. 298 children in Mbita, Western Kenya, with uncomplicated falciparum malaria were randomized to artemether-lumefantrine (AL, n = 153) ordihydroartemisinin-piperaquine (DP, n = 145). Parasite carriage post-treatment was determined by microscopy and qPCR, gametocyte carriage by quantitative nucleic acid sequence based amplication. Infectiousness to mosquitoes was determined by mosquito membrane feeding assays. Both drugs were efficacious as judged by standard trial outcomes. Sub-patent residual parasitaemia on day 3 was detected by qPCR in 36.11% (95% CI 25.11 - 48.29) of children treated with AL, and in 30.16% (95% CI 19.23 - 43.02) of children treated with DP. After adjustment for age, treatment arm and enrolment parasite density, children with an extended parasite clearance time were significantly more likely to have microscopically detected recurrent parasitaemia during follow-up (Odds Ratio: 19.51, 95% CI 5.24 - 72.71, p < 0.001). Children with an extended parasite clearance time were also more likely to be infectious to mosquitoes (Odds Ratio 2.76; 95% CI 1.14 - 6.67, p = 0.02) and gave rise to a higher oocyst load in mosquitoes (Incidence Rate Ratio 2.80, 95% CI 1.49 - 5.24, p = 0.001). Our findings indicate that an extended parasite clearance time after ACTs has consequences for the individual patient and for the population at large due to higher transmission potential. The high prevalence of residual subpatent parasitaemia after treatment may be due to novel parasite genotypes with reduced drug sensitivity, inadequate population-level immunity, or the higher sensitivity of qPCR for detection of persisting parasites.

Background Accurate sampling of sub-microscopic gametocytes is necessary for epidemiological studies to identify the infectious reservoir of Plasmodium falciparum. Detection of gametocyte mRNA achieves sensitive detection, but requires careful handling of samples. Filter papers can be used for collecting RNA samples, but rigorous testing of their capacity to withstand adverse storage conditions has not been fully explored. Methods Three gametocyte dilutions: 10/μL, 1.0/μL and 0.1/μL were spotted onto Whatman™ 903 Protein Saver Cards, FTA Classic Cards and 3MM filter papers that were stored under frozen, cold chain or tropical conditions for up to 13 weeks . RNA was extracted, then detected by quantitative nucleic acid sequence-based amplification (QT-NASBA) and reverse-transcriptase PCR (RT-PCR). Results Successful gametocyte detection was more frequently observed from the Whatman 903 Protein Saver Card compared to the Whatman FTA Classic Card, by both techniques (p Conclusions This study indicates the Whatman 903 Protein Saver Card is better for Pfs25 mRNA sampling compared to the Whatman FTA Classic Card, and that the Whatman 3MM filter paper may prove to be a satisfactory cheaper option for Pfs25 mRNA sampling. When appropriately dried, filter papers provide a useful approach to Pfs25 mRNA sampling, especially in settings where storage in RNA-protecting buffer is not possible.