Paracetamol may improve renal function in patients with severe Plasmodium knowlesi malaria, particularly in those with acute kidney injury and hemolysis, via inhibition of cell-free hemoglobin mediated oxidative kidney damage. We developed a population pharmacokinetic/pharmacodynamic (PK/PD) model to assess effects of paracetamol on creatinine, hepatotoxicity, fever clearance, and parasite clearance among Malaysian patients with predominantly non-severe knowlesi malaria using data from the PACKNOW trial (Clinical Trials Registration: NCT03056391). A total of 372 patients were included in the PK/PD analyses (paracetamol: n = 183, control: n = 189). Paracetamol PK was described using a prior PK model published in patients with falciparum malaria. The PK/PD demonstrated that higher paracetamol exposures were associated with a faster decline in both creatinine and fever clearance time, supporting its renoprotective and antipyretic effects. Increased paracetamol exposure was not associated with hepatotoxicity or serious adverse events, despite a weak positive association with liver transaminases over time. No significant relationship was observed between paracetamol exposure and parasite clearance. Overall, these findings highlight an exposure-response relationship for paracetamol and a decline in creatinine, supporting its use as a renoprotective drug in treating Plasmodium knowlesi malaria.

There are limited data on the tolerability and efficacy of pyronaridine-artesunate (Pyramax®) for the first-line treatment of Plasmodium falciparum malaria in children. A three-day course of Pyramax® plus one dose of primaquine was administered to 50 children and 70 adults (mean age of 13.8 and 31.6 years old, respectively) infected with P. falciparum in Krong Pa district, Gia Lai province in 2022 and 2023. The follow-up period was 42 days after commencement of treatment. Pyramax® was well-tolerated, with no serious adverse event reported. The PCR-adjusted adequate clinical and parasitological response at Day 42 in children was lower than in adults (86.7%, 39/45 vs 96.7%, 59/61; P=0.069). 44.9% (22/49) children and 54.3% (38/70) adults were detected with asexual parasites on Day 3, suggestive of partial artemisinin resistance. The six children, who experienced recrudescent malaria, had significantly higher median parasitemia on Day 0 (27,693 parasites/µL vs 13,395 parasites/µL; P=0.047) and lower median blood pyronaridine concentrations on Day 7 (33.0 ng/mL vs 49.2 ng/mL; P=0.106) compared to those who remained malaria-free by Day 42. The lower efficacy of Pyramax® in children is concerning and requires monitoring.

Inhibiting the inflammatory response to malaria offers a promising strategy to improve clinical outcomes and overcome immunoregulatory barriers that hinder development of antiparasitic immunity. We conducted a double-blind, randomized, placebo-controlled trial assessing whether ruxolitinib, a Janus-activated kinase (JAK) 1/2 inhibitor, can reduce inflammatory responses and enhance antiparasitic immunity in malaria-naïve volunteers inoculated with blood-stage Plasmodium falciparum . Twenty participants were inoculated and, on day 8, randomized to receive artemether-lumefantrine with either ruxolitinib or placebo. Ninety days later, participants underwent a second inoculation. Ruxolitinib was safe and well tolerated; moreover, it attenuated inflammatory responses to the initial infection, with reduced posttreatment increases in C-reactive protein and markers of disease severity, including angiopoietin-2 and intercellular adhesion molecule-1. Ruxolitinib also enhanced immune memory after the second infection, with elevated human leukocyte antigen–DRA and 4-1BB, consistent with increased T cell activation. These data support the further evaluation of ruxolitinib as an adjunctive treatment to improve clinical outcomes and boost antiparasitic immunity in clinical malaria.

OBJECTIVES:We assessed the therapeutic efficacy of pyronaridine-artesunate (Pyramax®) for the treatment of uncomplicated Plasmodium falciparum malaria in Gia Lai province, Central Vietnam where parasites are partially resistant to artemisinins. METHODS:In an open-label, single-arm trial, Pyramax® was administered to 120 patients (adults and children) infected with P. falciparum residing in Gia Lai province from March 2022 to December 2023. Patients received Pyramax® once daily for 3 days and single-dose primaquine under direct observation therapy. Patients' Day 7 blood pyronaridine concentrations were measured by liquid chromatography-mass spectrometry to determine drug exposure. RESULTS:After Pyramax® treatment, the proportion of patients with PCR-adjusted adequate clinical and parasitological response at Day 42 was 92.5% (95% CI: 85.5-96.2; 98/106). The median parasite and fever clearance times were 84 h (range: 24-132) and 36 h (range: 12-108), respectively. The median (IQR) parasite clearance half-life was 7.4 h (6.3-8.4), with 50.4% (60/119) of patients had parasites detected by microscopy at 72 h after commencing treatment, suggestive of partial artemisinin resistance. The eight patients who experienced malaria recrudescence had lower (P = 0.065) blood pyronaridine concentrations (mean 39.6 ng/mL, median 33.3 ng/mL, range: 12.4-90.5) compared to the 95 patients who were malaria-free by Day 42 (median 47.6 ng/mL, range: 10.6-123.0). CONCLUSIONS:Although Pyramax® remains efficacious in treating P. falciparum, the lower pyronaridine concentrations in patients who had recrudescent malaria are worrisome and suggest that reduced pyronaridine exposure may be responsible for the Pyramax® treatment failures.

Inhibiting the host inflammatory response to malaria represents a potential strategy to improve clinical outcomes and inhibit immunoregulatory pathways that underlie suboptimal development of antiparasitic immunity. Ruxolitinib is a JAK 1/2 inhibitor that reduces inflammatory biomarkers when used in myeloproliferative disorders, and inhibits type-1 interferons and enhances CD4+ T cell immunity when combined with anti-parasitic drugs in animal models. Here we report the results of a double-blind randomised placebo-controlled trial evaluating the ability of ruxolitinib to reduce inflammatory responses and boost anti-parasitic immunity in malaria-naive volunteers inoculated with blood-stage Plasmodium falciparum. Twenty participants were inoculated, and randomized on day 8 to receive artemether-lumefantrine with either ruxolitinib or placebo. Ninety days later, participants who remained eligible were re-inoculated with a second infection. Ruxolitinib was safe and well-tolerated, and attenuated the host inflammatory response to the initial infection, with reduced post-treatment increases in the inflammatory biomarker CRP, as well as markers of disease severity including angiopoietin-2 and ICAM-1. Further, ruxolitinib enhanced the immune memory response following a second inoculation, with increased plasma levels of HLA-DR and CXCL13, indicating enhanced immune activation and germinal centre responses, respectively. These data support the further evaluation of ruxolitinib as an adjunctive treatment to improve clinical outcomes and boost anti-parasitic immunity in clinical malaria. ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial Australian New Zealand Clinical Trials Registry (ACTRN12621000866808). ### Funding Statement This study was funded by the Australian National Health and Medical Research Council (NHMRC); Ideas Grant to BEB and MJB (GNT2002957). BEB and JCM are supported by NHMRC Investigator Grants (2016792 and 2016396 respectively); MJB is supported by a Snow Medical Fellowship (2022/SF167) and CSL Centenary Fellowship. The QIMR Berghofer Clinical Malaria group receives core funding from Medicines for Malaria Venture (MMV) to support the conduct of malaria volunteer infection studies. Work in the Stanford Human Immune Monitoring Center was supported by the Gates Foundation [INV-008378]. The conclusions and opinions expressed in this work are those of the author(s) alone and shall not be attributed to the Foundation. Under the grant conditions of the Foundation, a Creative Commons Attribution 4.0 License has already been assigned to the Author Accepted Manuscript version that might arise from this submission. Please note works submitted as a preprint have not undergone a peer review process. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was approved by the QIMR Berghofer Medical Research Institute Human Research Ethics Committee (P3696) and ethically reviewed in minimising duplication of ethics by the Australian Departments of Defence and Veterans Affairs Human Research Ethics Committee. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors. NUlisa and phospho CyTOF whole blood data is publicly available: DOI 10.5281/zenodo.15080321 and DOI 10.5281/zenodo.14872946

The emergence and spread of chloroquine-resistant Plasmodium vivax have necessitated the assessment of alternative blood schizonticidal drugs. In Vietnam, chloroquine-resistant P. vivax malaria has been reported. In an open-label, single-arm trial, the safety, tolerability, and efficacy of pyronaridine-artesunate (Pyramax, PA) was evaluated in Dak Nong province, Vietnam. A 3-day course of PA was administered to adults and children (>= 20 kg) infected with P. vivax. Patients also received primaquine (0.25 mg/kg daily for 14 days). PA was well tolerated with transient asymptomatic increases in liver transaminases. The per-protocol proportion of patients with day 42 PCR-unadjusted adequate clinical and parasitological response was 96.0% (95% CI, 84.9%-99.0%, n = 48/50). The median parasite clearance time was 12 h (range, 12-36 h), with a median fever clearance time of 24 h (range, 12-60 h). Single nucleotide polymorphisms (SNPs) as potential genetic markers of reduced drug susceptibility were analyzed in three putative drug resistance markers, Pvcrt-o, Pvmdr1, and PvK12. Insertion at position K10 of the Pvcrt-o gene was found in 74.6% (44/59) of isolates. Pvmdr1 SNPs at Y976F and F1076L were present in 61% (36/59) and 78% (46/59), respectively. Amplification of Pvmdr1 gene (two copies) was found in 5.1% (3/59) of parasite samples. Only 5.1% (3/59) of isolates had mutation 552I of the PvK12 gene. Overall, PA rapidly cleared P. vivax blood asexual stages and was highly efficacious in treating vivax malaria, with no evidence of artemisinin resistance found. PA provides an alternative to chloroquine treatment for vivax malaria in Vietnam. CLINICAL TRIALS This study is registered with the Australian New Zealand Clinical Trials Registry as ACTRN12618001429246.

BACKGROUND:Novel and highly sensitive point-of-care malaria diagnostic and surveillance tools that are rapid and affordable are urgently needed to support malaria control and elimination. METHODS:We demonstrated the potential of near-infrared spectroscopy (NIRS) technique to detect malaria parasites both, in vitro, using dilutions of infected red blood cells obtained from Plasmodium falciparum cultures and in vivo, in mice infected with P. berghei using blood spotted on slides and non-invasively, by simply scanning various body areas (e.g., feet, groin and ears). The spectra were analysed using machine learning to develop predictive models for infection. FINDINGS:Using NIRS spectra of in vitro cultures and machine learning algorithms, we successfully detected low densities (<10-7 parasites/μL) of P. falciparum parasites with a sensitivity of 96% (n = 1041), a specificity of 93% (n = 130) and an accuracy of 96% (n = 1171) and differentiated ring, trophozoite and schizont stages with an accuracy of 98% (n = 820). Furthermore, when the feet of mice infected with P. berghei with parasitaemia ≥3% were scanned non-invasively, the sensitivity and specificity of NIRS were 94% (n = 66) and 86% (n = 342), respectively. INTERPRETATION:These data highlights the potential of NIRS technique as rapid, non-invasive and affordable tool for surveillance of malaria cases. Further work to determine the potential of NIRS to detect malaria in symptomatic and asymptomatic malaria cases in the field is recommended including its capacity to guide current malaria elimination strategies.

The devastating impact of malaria includes significant mortality and illness worldwide. Increasing resistance of the causative parasite, Plasmodium, to existing antimalarial drugs underscores a need for additional compounds with distinct modes of action in the therapeutic development pipeline. Here we showcase peptide-drug conjugates (PDCs) as an attractive compound class, in which therapeutic or lead antimalarials are chemically conjugated to cell-penetrating peptides. This approach aims to enhance selective uptake into Plasmodium-infected red blood cells and impart additional cytotoxic actions on the intraerythrocytic parasite, thereby enabling targeted drug delivery and dual modes of action. We describe the development of PDCs featuring four compounds with antimalarial activity-primaquine, artesunate, tafenoquine and methotrexate-conjugated to three cell-penetrating peptide scaffolds with varied antiplasmodial activity, including active and inactive analogues of platelet factor 4 derived internalization peptide (PDIP), and a cyclic polyarginine peptide. Development of this diverse set of PDCs featured distinct and adaptable conjugation strategies, to produce conjugates with in vitro antiplasmodial activities ranging from low nanomolar to low micromolar potencies according to the drug cargo and bioactivity of the partner peptide. Overall, this study establishes a strategic and methodological framework for the further development of dual mode of action peptide-drug antimalarial therapeutics.

ABSTRACTBackgroundThe long acting 8-aminoquinoline tafenoquine may be a good candidate for mass drug administration if it exhibits sufficient blood stage antimalarial activity at doses low enough to be tolerated by glucose 6-phosphate dehydrogenase (G6PD) deficient individuals.MethodsHealthy G6PD-normal adults were inoculated withPlasmodium falciparum3D7-infected erythrocytes on day 0. Different single oral doses of tafenoquine were administered on day 8. Parasitemia, and concentrations of tafenoquine and the 5,6-orthoquinone metabolite in plasma/whole blood/urine were measured and standard safety assessments performed. Curative artemether-lumefantrine therapy was administered if parasite regrowth occurred, or on day 48±2. Outcomes were parasite clearance kinetics, pharmacokinetic and pharmacokinetic/pharmacodynamic (PK/PD) parameters from modelling, and dose simulations in a theoretical endemic population.ResultsTwelve participants were inoculated and administered 200 mg (n=3), 300 mg (n=4), 400 mg (n=2), or 600 mg (n=3) tafenoquine. The parasite clearance half-life with 400 mg or 600 mg (5.4 h and 4.2 h respectively) was faster than with 200 mg or 300 mg (11.8 h and 9.6 h respectively). Parasite regrowth occurred after dosing with 200 mg (3/3 participants) and 300 mg (3/4 participants), but not after 400 mg or 600 mg. Simulations using the PK/PD model predicted that 460 mg and 540 mg would clear parasitaemia by a factor of 106and 109, respectively, in a 60 kg adult.ConclusionsAlthough a single dose or tafenoquine exhibits potentP. falciparumblood stage antimalarial activity, the estimated doses to effectively clear asexual parasitemia will require prior screening to exclude G6PD deficiency.Main pointA single oral dose of tafenoquine is effective against blood stagePlasmodium falciparuminfection. However, as the estimated dose to clear asexual parasitaemia is ≥460 mg (in adults), prior screening for glucose 6-phosphate dehydrogenase deficiency will be required.

ABSTRACT Background Blocking the transmission of parasites from humans to mosquitoes is a key component of malaria control. Tafenoquine exhibits activity against all stages of the malaria parasite and may have utility as a transmission blocking agent. We aimed to characterize the transmission blocking activity of low dose tafenoquine. Methods Healthy adults were inoculated with P. falciparum 3D7-infected erythrocytes on day 0. Piperaquine was administered on days 9 and 11 to clear asexual parasitemia while allowing gametocyte development. A single 50 mg oral dose of tafenoquine was administered on day 25. Transmission was determined by enriched membrane feeding assays pre-dose and at 1, 4 and 7 days post-dose. Artemether-lumefantrine was administered following the final assay. Outcomes were the reduction in mosquito infection and gametocytemia post-tafenoquine, and safety parameters. Results Six participants were enrolled, and all were infective to mosquitoes pre-tafenoquine, with a median 86% (range: 22–98) of mosquitoes positive for oocysts and 57% (range: 4–92) positive for sporozoites. By day 4 post-tafenoquine, the oocyst and sporozoite positivity rate had reduced by a median 35% (IQR: 16–46) and 52% (IQR: 40–62), respectively, and by day 7, 81% (IQR 36–92) and 77% (IQR 52–98), respectively. The decline in gametocyte density post-tafenoquine was not significant. No significant participant safety concerns were identified. Conclusion Low dose tafenoquine reduces P. falciparum transmission to mosquitoes, with a delay in effect. Trial registration Australian New Zealand Clinical Trials Registry (ACTRN12620000995976). Funding QIMR Berghofer Medical Research Institute.

ABSTRACT Plasmodium vivax infections and relapses remain a major health problem for malaria-endemic countries, deployed military personnel, and travelers. Presumptive anti-relapse therapy and radical cure using the 8-aminoquinoline drugs primaquine and tafenoquine are necessary to prevent relapses. Although it has been demonstrated that the efficacy of primaquine is associated with Cytochrome P450 2D6 (CYP2D6) activity, there is insufficient data on the role of CYP2D6 in the anti-relapse efficacy of tafenoquine. We investigated the relationship between CYP2D6 activity status and tafenoquine efficacy in preventing P. vivax relapses retrospectively using plasma samples collected from Australian Defence Force personnel deployed to Papua New Guinea and Timor-Leste who participated in clinical trials of tafenoquine during 1999–2001. The CYP2D6 gene was amplified from plasma samples and fully sequenced from 92 participant samples, comprised of relapse ( n = 31) and non-relapse ( n = 61) samples, revealing 14 different alleles. CYP2D6 phenotypes deduced from combinations of CYP2D6 alleles predicted that among 92 participants 67, 15, and 10 were normal, intermediate, and poor metabolizers, respectively. The deduced CYP2D6 phenotype did not correlate with the corresponding participant’s plasma tafenoquine concentrations that were determined in the early 2000s by high-performance liquid chromatography or liquid chromatography-mass spectrometry. Furthermore, the deduced CYP2D6 phenotype did not associate with P. vivax relapse outcomes. Our results indicate that CYP2D6 does not affect plasma tafenoquine concentrations and the efficacy of tafenoquine in preventing P. vivax relapses in the assessed Australian Defence Force personnel.

Regularly-dosed acetaminophen did not improve renal function in all patients with knowlesi malaria. In predefined subgroups of severe malaria and acute kidney injury with hemolysis, acetaminophen improved renal function and may be considered a safe renoprotective adjunct in these groups. Background Acetaminophen inhibits cell-free hemoglobin-induced lipid peroxidation and improves renal function in severe falciparum malaria but has not been evaluated in other infections with prominent hemolysis, including Plasmodium knowlesi malaria. Methods PACKNOW was an open-label, randomized, controlled trial of acetaminophen (500 mg or 1000 mg every 6 hours for 72 hours) vs no acetaminophen in Malaysian patients aged >= 5 years with knowlesi malaria of any severity. The primary end point was change in creatinine at 72 hours. Secondary end points included longitudinal changes in creatinine in patients with severe malaria or acute kidney injury (AKI), stratified by hemolysis. Results During 2016-2018, 396 patients (aged 12-96 years) were randomized to acetaminophen (n = 199) or no acetaminophen (n = 197). Overall, creatinine fell by a mean (standard deviation) 14.9% (18.1) in the acetaminophen arm vs 14.6% (16.0) in the control arm (P = .81). In severe disease, creatinine fell by 31.0% (26.5) in the acetaminophen arm vs 20.4% (21.5) in the control arm (P = .12), and in those with hemolysis by 35.8% (26.7) and 19% (16.6), respectively (P = .07). No difference was seen overall in patients with AKI; however, in those with AKI and hemolysis, creatinine fell by 34.5% (20.7) in the acetaminophen arm vs 25.9% (15.8) in the control arm (P = .041). Mixed-effects modeling demonstrated a benefit of acetaminophen at 72 hours (P = .041) and 1 week (P = .002) in patients with severe malaria and with AKI and hemolysis (P = .027 and P = .002, respectively). Conclusions Acetaminophen did not improve creatinine among the entire cohort but may improve renal function in patients with severe knowlesi malaria and in those with AKI and hemolysis.

Analytical methods for the quantification of the new 8-aminoquinoline antimalarial tafenoquine (TQ) in human blood, plasma and urine, and the 5,6-orthoquinone tafenoquine metabolite (5,6-OQTQ) in human plasma and urine have been validated. The procedure involved acetonitrile extraction of samples followed by ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Chromatography was performed using a Waters Atlantis T3 column with a gradient of 0.1% formic acid and acetonitrile at a flow rate of 0.5 mL per minute for blood and plasma. Urine analysis was the same but with methanol containing 0.1% formic acid replacing acetonitrile mobile phase. The calibration range for TQ and 5,6-OQTQ in plasma was 1 to 1200 ng/mL, and in urine was 10 to 1000 ng/mL. Blood calibration range for TQ was 1 to 1200 ng/mL. Blood could not be validated for 5,6-OQTQ due to significant signal suppression. The inter-assay precision (coefficient of variation %) was 9.9% for TQ at 1 ng/mL in blood (n = 14) and 8.2% for TQ and 7.1% for 5,6-OQTQ at 1 ng/mL in plasma (n = 14). For urine, the inter-assay precision was 8.2% for TQ and 6.4% for 5,6-OQTQ at 10 ng/mL (n = 14). TQ and 5,6-OQTQ are stable in blood, plasma and urine for at least three months at both −80 °C and −20 °C. Once validated, the analytical methods were applied to samples collected from healthy volunteers who were experimentally infected with Plasmodium falciparum to evaluate the blood stage antimalarial activity of TQ and to determine the therapeutic dose estimates for TQ, the full details of which will be published elsewhere. In this study, the measurement of TQ and 5,6-OQTQ concentrations in samples from one of the four cohorts of participants is reported. Interestingly, TQ urine concentrations were proportional to parasite recrudescence times post dosing To our knowledge, this is the first description of a fully validated method for the measurement of TQ and 5,6-OQTQ quantification in urine.

Abstract Background Malaria elimination by 2030 is an aim of many countries in the Greater Mekong Sub-region, including Vietnam. However, to achieve this goal and accelerate towards malaria elimination, countries need to determine the extent and prevalence of asymptomatic malaria as a potential reservoir for malaria transmission and the intensity of malaria transmission. The purpose of this study was to determine the prevalence of asymptomatic malaria and seropositivity rate in several districts of Gia Lai province in the Central Highlands of Vietnam. Methods A cross-sectional survey of asymptomatic malaria and serological testing was conducted in 3283 people living at 14 communes across seven districts in Gia Lai province in December 2016 to January 2017. Finger prick capillary blood samples were tested for malaria using rapid diagnostic testing and polymerase chain reaction (PCR), as well as detecting antibodies against 3 Plasmodium falciparum and 4 Plasmodium vivax antigens by indirect enzyme-linked immunosorbent assay (ELISA). Age-seroprevalence curves were fitted using reverse catalytic models with maximum likelihood. Results The study population was predominantly male (65.9%, 2165/3283), adults (88.7%, 2911/3283) and of a minority ethnicity (72.2%, 2371/3283), with most participants being farmers and outdoor government workers (90.2%, 2960/3283). Using a small volume of blood (≈ 10 µL) the PCR assay revealed that 1.74% (57/3283) of the participants had asymptomatic malaria (P. falciparum 1.07%, P. vivax 0.40%, Plasmodium malariae 0.15% and mixed infections 0.12%). In contrast, the annual malaria prevalence rates for clinical malaria in the communities where the participants lived were 0.12% (108/90,395) in 2016 and 0.22% (201/93,184) in 2017. Seropositivity for at least one P. falciparum or one P. vivax antigen was 38.5% (1257/3262) and 31.1% (1022/3282), respectively. Age-dependent trends in the proportion of seropositive individuals in five of the districts discriminated the three districts with sustained low malaria prevalence from the two districts with higher transmission. Conclusions Asymptomatic Plasmodium carriers were found to be substantially more prevalent than clinical cases in seven districts of Gia Lai province, and a third of the population had serological evidence of previous malaria exposure. The findings add knowledge on the extent of asymptomatic malaria and transmission for developing malaria elimination strategies for Vietnam.

The rise in Plasmodium falciparum resistance to dihydroartemisinin-piperaquine in Vietnam justifies the need to evaluate alternative artemisinin-based combination therapies. Between July 2018 and October 2019, a single-arm trial of pyronaridine-artesunate (Pyramax, PA) was conducted in Dak Nong province, Vietnam. PA ( 3-day course) was administered to adults and children infected with P. falciparum. PA was well tolerated by the participants. The proportion of patients with Day 42 PCR-corrected adequate clinical and parasitological response was 95.2% (95% confidence interval [CI], 82.3 to 98.8, n = 40/42) for treating falciparum malaria. The median parasite clearance half-life was 6.7 h (range, 2.6 to 11.9) and the median parasite clearance time was 72 h (range, 12 to 132) with 44.9% (22/49) of patients having positive blood films at 72 h. The two patients that recrudesced had comparable Day 7 blood pyronaridine concentrations (39.5 and 39.0 ng/ml) to the 40 patients who did not recrudesce (median 43.4 ng/ml, 95% CI, 35.1 to 54.9). Ring- stage and piperaquine survival assays revealed that of the 29 P. falciparum isolates collected from the patients before PA treatment, 22 (75.9%) had reduced susceptibility to artemisinins and 17 (58.6%) were resistant to piperaquine. Genotyping confirmed that 92.0% ( 46/50) of falciparum patients were infected with parasites bearing the Pfkelch13 C580Y mutation associated with artemisinin resistance. Of these, 56.0% (28/ 50) of the isolates also had multiple copies of the plasmepsin 2/3 genes responsible for piperaquine resistance. Overall, PA was effective in treating P. falciparum in the Central Highlands of Vietnam.

Novel 3,3'-disubstituted-5,5'-bi(1,2,4-triazine) compounds with potent in vitro activity against Plasmodium falciparum parasites were recently discovered. To improve the pharmacokinetic properties of the triazine derivatives, a new structure-activity relationship (SAR) investigation was initiated with a focus on enhancing the metabolic stability of lead compounds. These efforts led to the identification of second-generation highly potent antimalarial bis-triazines, exemplified by triazine 23, which exhibited significantly improved in vitro metabolic stability (8 and 42 μL/min/mg protein in human and mouse liver microsomes). The disubstituted triazine dimer 23 was also observed to suppress parasitemia in the Peters 4-day test with a mean ED50 value of 1.85 mg/kg/day and exhibited a fast-killing profile, revealing a new class of orally available antimalarial compounds of considerable interest.

Plasmodium falciparum resistance to dihydroartemisinin-piperaquine has spread through the Greater Mekong Subregion to southwestern Vietnam. In 2018 to 2019, we collected 127 P. falciparum isolates from Dak Nong (36), Dak Lak (55), Gia Lai (13), and Kon Tum (23) provinces in Vietnam's Central Highlands and found parasites bearing the Pfkelch13 C580Y mutation and multiple plasmepsin 2/3 genes (mean prevalence, 17.9%; range, 4.3% to 27.8%), conferring resistance to dihydroartemisinin-piperaquine. This information is important for drug policy decisions in Vietnam.

Asymptomatic parasite carriers represent a “silent” infective reservoir for malaria transmission and contributes to malaria persistence. However, limited data are available on asymptomatic malaria in Vietnam. Between November 2018 and March 2019, we conducted a malaria epidemiological survey of asymptomatic people (children ≥ 10 years old and adults ≥18 years old, n = 2,809) residing in three communes in Tuy Duc district, Dak Nong province in the Central Highlands of Vietnam. Based on the national stratification of malaria risk, Dak Buk So, Dak Ngo and Quang Truc communes were classified by the National Malaria Control Programme as low, moderate and high malaria endemic areas, respectively. Using participants’ finger prick blood samples, malaria parasites were detected by one-step reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The median age (Interquartile Range) for adults and children were 35 years (26–50) and 12 years (11–14), respectively. The prevalence of asymptomatic malaria was 1.7% (22/1,328), 3.5% (31/890) and 12.2% (72/591) for participants from Dak Buk So, Dak Ngo and Quang Truc, respectively. The prevalence of asymptomatic malaria was lower in children compared to adults: 2.6% (9/352) versus 4.7% (116/2,457) (Odds Ratio 0.53, 95% Confidence Interval 0.28 to1.02). Ownership of long-lasting insecticide-treated bed nets and hammocks was 97.1%, 99.0% and 94.7% for participants in Dak Buk So, Dak Ngo and Quang Truc, respectively, however, only 66.0%, 57.3% and 42.8% of the participants reported using bed nets every night. Of the several risk factors examined, going to the forest two weeks prior to enrolment into the study and sleeping in the forest had a significant association with participants being infected with asymptomatic malaria in Quang Truc, but not in the other two communes. Knowledge of the prevalence and distribution of asymptomatic malaria will help design and evaluate future intervention strategies for malaria elimination in Vietnam.