Elizabeth A AshleyKasia StepniewskaCarole FoggMarion BarendsRoger TwesigyeLily KeereecharoenJames KiguliCarit ler MooCarolyn NabasumbaAnchalee JaideeVincent BatwalaKhin Maung LwinPatrice PiolaRose McGreadyPhilippe J GuerinKesinee Chotivanichเกศินี โชติวานิชHugh KingstonArjen DondorpNicholas J WhiteFrançois NostenCharles J WoodrowMahidol University. Faculty of Tropical Medicine. Mahidol-Oxford Tropical Medicine Research Unit2015-06-292021-08-172015-06-292021-08-172015-06-292014https://repository.li.mahidol.ac.th/handle/20.500.14594/63145Joint International Tropical Medicine Meeting 2014: 3D perspectives on tropical medicine: drivers, diversity and determination the 8th seminar on food-and water-borne parasitic zoonoses: 2-4 December 2014: Centara Grand Bangkok Convention Center at Central World, Bangkok, Thailand. Bangkok: Faculty of Tropical Medicine, Mahidol University; 2014. p. 227.The most sensitive rapid diagnostic tests of P. falciparum are based on detection of histidine-rich protein 2 (HRP2), but HRP2 persists in the blood after treatment and cannot be used to assess treatment response. We measured antigen levels over a 4-week period in ACT-treated hyperparasitaemic patients with P. falciparum in Uganda and Thailand (prior to the emergence of artemisinin resistance). Antigen clearance was quantified by calculation of area-undercurve (AUC) after normalization to baseline antigen level. Whole blood HRP2 levels showed a wide range of AUCs: Uganda median 415 d·% (range 48–2588); Thailand 590 d·% (33–1534). The primary determinant of AUC was admission stage; in patients presenting with >75% tiny/small rings (32/40 in Uganda, 24/38 in Thailand), median HRP2 AUCs were respectively 6.4 and 10.7-fold higher than cases with later stages (p=0.0005, <0.0001). Stage was also a key determinant of the time for the Paracheckä RDT to become negative during follow-up. These data support the hypothesis that the mechanism for HRP2 persistence is pitting in the spleen since once-infected erythrocytes returning to the circulation can provide a source for persistently high levels of HRP2 and ongoing positivity of HRP2-based RDTs.engMahidol UniversityMalariaProceeding Poster