Artemether-Lumefantrine Versus Chloroquine for the Treatment of Uncomplicated Plasmodium knowlesi Malaria: An Open-Label Randomized Controlled Trial CAN KNOW

Longitudinal changes in iron homeostasis in human experimental and clinical malaria

Background

The interaction between iron deficiency and malaria is incompletely understood. We evaluated longitudinal changes in iron homeostasis in volunteers enrolled in malaria volunteer infection studies (VIS) and in Malaysian patients with falciparum and vivax malaria.

Methods

We retrieved samples and associated data from 55 participants enrolled in malaria VIS, and 171 malaria patients and 30 healthy controls enrolled in clinical studies in Malaysia. Ferritin, hepcidin, erythropoietin, and soluble transferrin receptor (sTfR) were measured by ELISA.

Results

In the VIS, participants' parasitaemia was correlated with baseline mean corpuscular volume (MCV), but not iron status (ferritin, hepcidin or sTfR). Ferritin, hepcidin and sTfR all increased during the VIS. Ferritin and hepcidin normalised by day 28, while sTfR remained elevated. In VIS participants, baseline iron status (ferritin) was associated with post-treatment increases in liver transaminase levels. In Malaysian malaria patients, hepcidin and ferritin were elevated on admission compared to healthy controls, while sTfR increased following admission. Hepcidin normalised by day 28; however, ferritin and sTfR both remained elevated 4 weeks following admission.

Conclusion

Our findings demonstrate that parasitaemia is associated with an individual's MCV rather than iron status. The persistent elevation in sTfR 4 weeks post-infection in both malaria VIS and clinical malaria may reflect a causal link between malaria and iron deficiency.

Single cell transcriptomics shows that malaria promotes unique regulatory responses across multiple immune cell subsets

Plasmodium falciparum malaria drives immunoregulatory responses across multiple cell subsets, which protects from immunopathogenesis, but also hampers the development of effective anti-parasitic immunity. Understanding malaria induced tolerogenic responses in specific cell subsets may inform development of strategies to boost protective immunity during drug treatment and vaccination. Here, we analyse the immune landscape with single cell RNA sequencing during P. falciparum malaria. We identify cell type specific responses in sub-clustered major immune cell types. Malaria is associated with an increase in immunosuppressive monocytes, alongside NK and γδ T cells which up-regulate tolerogenic markers. IL-10-producing Tr1 CD4 T cells and IL-10-producing regulatory B cells are also induced. Type I interferon responses are identified across all cell types, suggesting Type I interferon signalling may be linked to induction of immunoregulatory networks during malaria. These findings provide insights into cell-specific and shared immunoregulatory changes during malaria and provide a data resource for further analysis.

Quantification of parasite clearance in Plasmodium knowlesi infections

BACKGROUND

The incidence of zoonotic Plasmodium knowlesi infections in humans is rising in Southeast Asia, leading to clinical studies to monitor the efficacy of anti-malarial treatments for knowlesi malaria. One of the key outcomes of anti-malarial drug efficacy is parasite clearance. For Plasmodium falciparum, parasite clearance is typically estimated using a two-stage method, that involves estimating parasite clearance for individual patients followed by pooling of individual estimates to derive population estimates. An alternative approach is Bayesian hierarchical modelling which simultaneously analyses all parasite-time patient profiles to determine parasite clearance. This study compared these methods for estimating parasite clearance in P. knowlesi treatment efficacy studies, with typically fewer parasite measurements per patient due to high susceptibility to anti-malarials.

METHODS

Using parasite clearance data from 714 patients with knowlesi malaria and enrolled in three trials, the Worldwide Antimalarial Resistance Network (WWARN) Parasite Clearance Estimator (PCE) standard two-stage approach and Bayesian hierarchical modelling were compared. Both methods estimate the parasite clearance rate from a model that incorporates a lag phase, slope, and tail phase for the parasitaemia profiles.

RESULTS

The standard two-stage approach successfully estimated the parasite clearance rate for 678 patients, with 36 (5%) patients excluded due to an insufficient number of available parasitaemia measurements. The Bayesian hierarchical estimation method was applied to the parasitaemia data of all 714 patients. Overall, the Bayesian method estimated a faster population mean parasite clearance (0.36/h, 95% credible interval [0.18, 0.65]) compared to the standard two-stage method (0.26/h, 95% confidence interval [0.11, 0.46]), with better model fits (compared visually). Artemisinin-based combination therapy (ACT) is more effective in treating P. knowlesi than chloroquine, as confirmed by both methods, with a mean estimated parasite clearance half-life of 2.5 and 3.6 h, respectively using the standard two-stage method, and 1.8 and 2.9 h using the Bayesian method.

CONCLUSION

For clinical studies of P. knowlesi with frequent parasite measurements, the standard two-stage approach (WWARN's PCE) is recommended as this method is straightforward to implement. For studies with fewer parasite measurements per patient, the Bayesian approach should be considered. Regardless of method used, ACT is more efficacious than chloroquine, confirming the findings of the original trials.

Diagnostic accuracy and limit of detection of ten malaria parasite lactate dehydrogenase-based rapid tests for Plasmodium knowlesi and P. falciparum

Background

Plasmodium knowlesi causes zoonotic malaria across Southeast Asia. First-line diagnostic microscopy cannot reliably differentiate P. knowlesi from other human malaria species. Rapid diagnostic tests (RDTs) designed for P. falciparum and P. vivax are used routinely in P. knowlesi co-endemic areas despite potential cross-reactivity for species-specific antibody targets.

Methods

Ten RDTs were evaluated: nine to detect clinical P. knowlesi infections from Malaysia, and nine assessing limit of detection (LoD) for P. knowlesi (PkA1-H.1) and P. falciparum (Pf3D7) cultures. Targets included Plasmodium-genus parasite lactate dehydrogenase (pan-pLDH) and P. vivax (Pv)-pLDH.

Results

Samples were collected prior to antimalarial treatment from 127 patients with microscopy-positive PCR-confirmed P. knowlesi mono-infections. Median parasitaemia was 788/µL (IQR 247-5,565/µL). Pan-pLDH sensitivities ranged from 50.6% (95% CI 39.6–61.5) (SD BIOLINE) to 87.0% (95% CI 75.1–94.6) (First Response^® and CareStart™ PAN) compared to reference PCR. Pv-pLDH RDTs detected P. knowlesi with up to 92.0% (95% CI 84.3-96.7%) sensitivity (Biocredit™). For parasite counts ≥200/µL, pan-pLDH (Standard Q) and Pv-pLDH RDTs exceeded 95% sensitivity. Specificity of RDTs against 26 PCR-confirmed negative controls was 100%. Sensitivity of six highest performing RDTs were not significantly different when comparing samples taken before and after (median 3 hours) antimalarial treatment. Parasite ring stages were present in 30% of pre-treatment samples, with ring stage proportions (mean 1.9%) demonstrating inverse correlation with test positivity of Biocredit™ and two CareStart™ RDTs.

For cultured P. knowlesi, CareStart™ PAN demonstrated the lowest LoD at 25 parasites/µL; LoDs of other pan-pLDH ranged from 98 to >2000 parasites/µL. Pv-pLDH LoD for P. knowlesi was 49 parasites/µL. No false-positive results were observed in either P. falciparum-pLDH or histidine-rich-protein-2 channels.

Conclusion

Selected RDTs demonstrate sufficient performance for detection of major human malaria species including P. knowlesi in co-endemic areas where microscopy is not available, particularly for higher parasite counts, although cannot reliably differentiate among non-falciparum malaria.

Clinical management of Plasmodium knowlesi malaria

The zoonotic parasite Plasmodium knowlesi has emerged as an important cause of human malaria in parts of Southeast Asia. The parasite is indistinguishable by microscopy from the more benign P. malariae, but can result in high parasitaemias with multiorgan failure, and deaths have been reported. Recognition of severe knowlesi malaria, and prompt initiation of effective therapy is therefore essential to prevent adverse outcomes. Here we review all studies reporting treatment of uncomplicated and severe knowlesi malaria. We report that although chloroquine is effective for the treatment of uncomplicated knowlesi malaria, artemisinin combination treatment is associated with faster parasite clearance times and lower rates of anaemia during follow-up, and should be considered the treatment of choice, particularly given the risk of administering chloroquine to drug-resistant P. vivax or P. falciparum misdiagnosed as P. knowlesi malaria in co-endemic areas. For severe knowlesi malaria, intravenous artesunate has been shown to be highly effective and associated with reduced case-fatality rates, and should be commenced without delay. Regular paracetamol may also be considered for patients with severe knowlesi malaria or for those with acute kidney injury, to attenuate the renal damage resulting from haemolysis-induced lipid peroxidation.

Knowlesi malaria: Human risk factors, clinical spectrum, and pathophysiology

Plasmodium knowlesi is endemic across Southeast Asia, and is the commonest cause of zoonotic malaria. The spectrum of clinical disease from P. knowlesi infection ranges from asymptomatic infection, through to severe malaria and death. Over 90% of clinical disease occurs in adults, mostly living in forest edge areas undergoing intensive land use change. With a 24-h asexual life cycle in humans, high parasite counts are possible, but most clinical cases of knowlesi malaria are uncomplicated with low parasitaemia. In co-endemic areas, median parasitaemia in knowlesi malaria is lower than that seen in vivax and falciparum malaria, suggesting a lower fever threshold. Severe malaria occurs in 6-9% of symptomatic adults. Manifestations of severe malaria from P. knowlesi are similar to those seen with falciparum malaria, with the notable absence of coma. Age, parasitaemia, cardiovascular comorbidities and delayed diagnosis are risk factors for severe disease and death, which are only seen in adults. Thrombocytopenia is near-universal in adults, likely related to platelet-red cell binding and clearance. Mechanisms underlying the microvascular sludging seen in fatal disease in non-natural primate hosts and the microvascular accumulation of parasites in fatal human disease are not clear. Marked reductions in deformability of both infected and uninfected red blood cells are associated with disease severity in both humans and other non-natural primate hosts, likely contributing to impaired microvascular perfusion and organ dysfunction. Endothelial activation, endothelial dysfunction, glycocalyx degradation and haemolysis are also associated with, and likely contribute to, severe disease and organ dysfunction, particularly acute kidney injury.

Plasmodium knowlesi detection methods for human infections-Diagnosis and surveillance

Within the overlapping geographical ranges of P. knowlesi monkey hosts and vectors in Southeast Asia, an estimated 1.5 billion people are considered at risk of infection. P. knowlesi can cause severe disease and death, the latter associated with delayed treatment occurring from misdiagnosis. Although microscopy is a sufficiently sensitive first-line tool for P. knowlesi detection for most low-level symptomatic infections, misdiagnosis as other Plasmodium species is common, and the majority of asymptomatic infections remain undetected. Current point-of-care rapid diagnostic tests demonstrate insufficient sensitivity and poor specificity for differentiating P. knowlesi from other Plasmodium species. Molecular tools including nested, real-time, and single-step PCR, and loop-mediated isothermal amplification (LAMP), are sensitive for P. knowlesi detection. However, higher cost and inability to provide the timely point-of-care diagnosis needed to guide appropriate clinical management has limited their routine use in most endemic clinical settings. P. knowlesi is likely underdiagnosed across the region, and improved diagnostic and surveillance tools are required. Reference laboratory molecular testing of malaria cases for both zoonotic and non-zoonotic Plasmodium species needs to be more widely implemented by National Malaria Control Programs across Southeast Asia to accurately identify the burden of zoonotic malaria and more precisely monitor the success of human-only malaria elimination programs. The implementation of specific serological tools for P. knowlesi would assist in determining the prevalence and distribution of asymptomatic and submicroscopic infections, the absence of transmission in certain areas, and associations with underlying land use change for future spatially targeted interventions.

The pharmacokinetic properties of artemether and lumefantrine in Malaysian patients with Plasmodium knowlesi malaria

AIMS

The aim of this study was to assess the pharmacokinetic properties of artemether, lumefantrine and their active metabolites in Plasmodium knowlesi malaria.

METHODS

Malaysian adults presenting with uncomplicated P. knowlesi infections received six doses of artemether (1.7 mg/kg) plus lumefantrine (10 mg/kg) over 3 days. Venous blood and dried blood spot (DBS) samples were taken at predetermined time-points over 28 days. Plasma and DBS artemether, dihydroartemisinin, lumefantrine and desbutyl-lumefantrine were measured using liquid chromatography-mass spectrometry. Multi-compartmental population pharmacokinetic models were developed using plasma with or without DBS drug concentrations.

RESULTS

Forty-one participants (mean age 45 years, 66% males) were recruited. Artemether-lumefantrine treatment was well tolerated and parasite clearance was prompt. Plasma and DBS lumefantrine concentrations were in close agreement and were used together in pharmacokinetic modelling, but only plasma concentrations of the other analytes were used because of poor correlation with DBS levels. The areas under the concentration-time curve (AUC_0-∞ ) for artemether, dihydroartemisinin and lumefantrine (medians 1626, 1881 and 625 098 μg.h/L, respectively) were similar to those reported in previous pharmacokinetic studies in adults and children. There was evidence of auto-induction of artemether metabolism (mean increase in clearance relative to bioavailability 25.2% for each subsequent dose). The lumefantrine terminal elimination half-life (median 9.5 days) was longer than reported in healthy volunteers and adults with falciparum malaria.

CONCLUSION

The disposition of artemether, dihydroartemisinin and lumefantrine in knowlesi malaria largely parallels that in other human malarias. DBS lumefantrine concentrations can be used in pharmacokinetic studies but DBS technology is currently unreliable for the other analytes.

A population of CD4hiCD38hi T cells correlates with disease severity in patients with acute malaria

OBJECTIVE

CD4⁺ T cells are critical mediators of immunity to Plasmodium spp. infection, but their characteristics during malarial episodes and immunopathology in naturally infected adults are poorly defined. Flow cytometric analysis of PBMCs from patients with either P. falciparum or P. knowlesi malaria revealed a pronounced population of CD4⁺ T cells co-expressing very high levels of CD4 and CD38 we have termed CD4^hiCD38^hi T cells. We set out to gain insight into the function of these novel cells.

METHODS

CD4⁺ T cells from 18 patients with P. falciparum or P. knowlesi malaria were assessed by flow cytometry and sorted into populations of CD4^hiCD38^hi or CD4^norm T cells. Gene expression in the sorted populations was assessed by qPCR and NanoString.

RESULTS

CD4^hiCD38^hi T cells expressed high levels of CD4 mRNA and canonical type 1 regulatory T-cell (TR1) genes including IL10, IFNG, LAG3 and HAVCR2 (TIM3), and other genes with relevance to cell migration and immunomodulation. These cells increased in proportion to malaria disease severity and were absent after parasite clearance with antimalarials.

CONCLUSION

In naturally infected adults with acute malaria, a prominent population of type 1 regulatory T cells arises that can be defined by high co-expression of CD4 and CD38 (CD4^hiCD38^hi) and that correlates with disease severity in patients with falciparum malaria. This study provides fundamental insights into T-cell biology, including the first evidence that CD4 expression is modulated at the mRNA level. These findings have important implications for understanding the balance between immunity and immunopathology during malaria.

Assessment of Chloroquine and Hydroxychloroquine Safety Profiles: A Systematic Review and Meta-Analysis

BACKGROUND

Chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) have recently emerged as potential antiviral and immunomodulatory options for the treatment of 2019 coronavirus disease (COVID-19). To examine the safety profiles of these medications, we systematically evaluated the adverse events (AEs) of these medications from published randomized controlled trials (RCTs).

METHODS

We systematically searched MEDLINE, the Cochrane library, the Cochrane Central Register of Controlled Trials (CENTRAL), and the ClinicalTrials.gov for all the RCTs comparing CQ or HCQ with placebo or other active agents, published before June 20, 2020. The random-effects or fixed-effects models were used to pool the risk estimates relative ratio (RR) with 95% confidence interval (CI) for the outcomes.

RESULTS

The literature search yielded 23 and 19 studies for CQ and HCQ, respectively, that satisfied our inclusion criteria. Of these studies, we performed meta-analysis on 6 studies for CQ and 18 studies for HCQ. We did not limit our analysis to published records involving viral treatment alone; data also included the usage of either CQ or HCQ for the treatment of other diseases. The trials for the CQ consisted of a total of 2,137 participants (n = 1,077 CQ, n = 1,060 placebo), while the trials for HCQ involved 2,675 participants (n = 1,345 HCQ and n = 1,330 control). The overall mild and total AEs were significantly higher in CQ-treated non-COVID-19 patients, HCQ-treated non-COVID-19 patients, and HCQ-treated COVID-19 patients. The AEs were further categorized into four groups and analyses revealed that neurologic, gastrointestinal (GI), dermatologic, and sensory AEs were higher in participants taking CQ compared to placebo, while GI, dermatologic, sensory, and cardiovascular AEs were higher in HCQ-treated COVID-19 patients compared to control patients. Moreover, subgroup analysis suggested higher AEs with respect to dosage and duration in HCQ group. Data were acquired from studies with perceived low risk of bias, so plausible bias is unlikely to seriously affect the main findings of the current study.

CONCLUSIONS

Taken together, we found that participants taking either CQ or HCQ exhibited more AEs than participants taking placebo or control. Precautionary measures should be taken when using these drugs to treat COVID-19. The meta-analysis was registered on OSF (https://osf.io/jm3d9).

REGISTRATION

The meta-analysis was registered on OSF (https://osf.io/jm3d9).

Antiphosphatidylserine Immunoglobulin M and Immunoglobulin G Antibodies Are Higher in Vivax Than Falciparum Malaria, and Associated With Early Anemia in Both Species

BACKGROUND

Anemia is a major complication of vivax malaria. Antiphosphatidylserine (PS) antibodies generated during falciparum malaria mediate phagocytosis of uninfected red blood cells that expose PS and have been linked to late malarial anemia. However, their role in anemia from non-falciparum Plasmodium species is not known, nor their role in early anemia from falciparum malaria.

METHODS

We measured PS immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies in Malaysian patients with vivax, falciparum, knowlesi, and malariae malaria, and in healthy controls, and correlated antibody titres with hemoglobin. PS antibodies were also measured in volunteers experimentally infected with Plasmodium vivax and Plasmodium falciparum.

RESULTS

PS IgM and IgG antibodies were elevated in patients with vivax, falciparum, knowlesi, and malariae malaria (P < .0001 for all comparisons with controls) and were highest in vivax malaria. In vivax and falciparum malaria, PS IgM and IgG on admission correlated inversely with admission and nadir hemoglobin, controlling for parasitemia and fever duration. PS IgM and IgG were also increased in volunteers infected with blood-stage P. vivax and P. falciparum, and were higher in P. vivax infection.

CONCLUSIONS

PS antibodies are higher in vivax than falciparum malaria, correlate inversely with hemoglobin, and may contribute to the early loss of uninfected red blood cells found in malarial anemia from both species.

Assessment of Hydroxychloroquine and Chloroquine Safety Profiles: A Systematic Review and Meta-Analysis

BACKGROUND

Recently, chloroquine (CQ) and its derivative hydroxychloroquine (HCQ) have emerged as potential antiviral and immunomodulatory options for the treatment of 2019 coronavirus disease (COVID-19). To examine the safety profiles of these medications, we systematically evaluated the adverse events (AEs) of these medications from published randomized controlled trials (RCTs).

METHODS

We systematically searched PubMed, MEDLINE, Cochrane, the Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE, and the ClinicalTrials.gov for all the RCTs comparing CQ or HCQ with placebo or other active agents, published before March 31, 2020. The random-effects or fixed-effects models were used to pool the risk estimates relative ratio (RR) with 95% confidence interval (CI) for the outcomes.

RESULTS

The literature search yielded 23 and 17 studies for CQ and HCQ, respectively, that satisfied our inclusion criteria. Of these studies, we performed meta-analysis on the ones that were placebo-controlled, which included 6 studies for CQ and 14 studies for HCQ. We did not limit our analysis to published reports involving viral treatment alone; data also included the usage of either CQ or HCQ for the treatment of other diseases. The trials for the CQ consisted of a total of 2,137 participants (n=1,077 CQ, n=1,060 placebo), while the trials for HCQ involved 1,096 participants (n=558 HCQ and n=538 placebo). The overall mild or total AEs were statistically higher comparing CQ or HCQ to placebo. The AEs were further categorized into four groups and analyses revealed that neurologic, gastrointestinal, dermatologic, and ophthalmic AEs were higher in participants taking CQ compared to placebo. Although this was not evident in HCQ treated groups, further analyses suggested that there were more AEs attributed to other organ system that were not included in the categorized meta-analyses. Additionally, meta-regression analyses revealed that total AEs was affected by dosage for the CQ group.

CONCLUSIONS

Taken together, we found that participants taking either CQ or HCQ have more AEs than participants taking placebo. Precautionary measures should be taken when using these drugs to treat COVID-19.

Identification of Plasmodium knowlesi Merozoite Surface Protein-119 (PkMSP-119 ) novel binding peptides from a phage display library

OBJECTIVE

Plasmodium knowlesi, the fifth human malaria parasite, has caused mortality in humans. We aimed to identify P. knowlesi novel binding peptides through a random linear dodecapeptide phage display targeting the 19-kDa fragment of Merozoite Surface Protein-1 protein.

METHODS

rPkMSP-1₁₉ protein was heterologously expressed using Expresso^® Solubility and Expression Screening System and competent E. cloni^® 10G cells according to protocol. Three rounds of biopanning were performed on purified rPkMSP-1₁₉ to identify binding peptides towards rPkMSP-1₁₉ using Ph.D.™-12 random phage display library. Binding sites of the identified peptides to PkMSP-1₁₉ were in silico predicted using the CABS-dock web server.

RESULTS

Four phage peptide variants that bound to PkMSP-1₁₉ were identified after three rounds of biopanning, namely Pkd1, Pkd2, Pkd3 and Pkd4. The sequences of both Pkd1 and Pkd2 consist of a large number of histidine residues. Pkd1 showed positive binding signal with 6.1× vs. BSA control. Docking results showed that Pkd1 and Pkd2 were ideal binding peptides for PkMSP-1₁₉ .

CONCLUSION

We identified two novel binding peptides of PkMSP-1₁₉ , Pkd1 (HFPFHHHKLRAH) and Pkd2 (HPMHMLHKRQHG), through phage display. They provide a valuable starting point for the development of novel therapeutics.

Malaria: What's New in the Management of Malaria?

The global burden of malaria remains high, with 216 million cases causing 445,000 deaths in 2016 despite first-line treatment with artemisinin-based combination therapy. Decreasing transmission in Africa shifts the risk for severe malaria to older age groups as premunition wanes. Prompt diagnosis and treatment with intravenous artesunate in addition to appropriate supportive management are critical to reduce deaths from severe malaria. Effective individual management is challenging in settings with limited resources for higher-level care. Adjunctive therapies targeting the underlying pathophysiological pathways have the potential to reduce mortality. Resistance to artemisinin derivatives and their partner drugs threaten malaria management and control.

IgM in human immunity to Plasmodium falciparum malaria

Most studies on human immunity to malaria have focused on the roles of immunoglobulin G (IgG), whereas the roles of IgM remain undefined. Analyzing multiple human cohorts to assess the dynamics of malaria-specific IgM during experimentally induced and naturally acquired malaria, we identified IgM activity against blood-stage parasites. We found that merozoite-specific IgM appears rapidly in Plasmodium falciparum infection and is prominent during malaria in children and adults with lifetime exposure, together with IgG. Unexpectedly, IgM persisted for extended periods of time; we found no difference in decay of merozoite-specific IgM over time compared to that of IgG. IgM blocked merozoite invasion of red blood cells in a complement-dependent manner. IgM was also associated with significantly reduced risk of clinical malaria in a longitudinal cohort of children. These findings suggest that merozoite-specific IgM is an important functional and long-lived antibody response targeting blood-stage malaria parasites that contributes to malaria immunity.

Human challenge models: tools to accelerate the development of malaria vaccines

INTRODUCTION

Malaria challenge models, where healthy human volunteers are intentionally infected with Plasmodium species parasites under controlled conditions, can be undertaken in several well-defined ways. These challenge models enable evaluation of the kinetics of parasite growth and clearance, host-pathogen interactions and the host immune response. They can facilitate discovery of candidate diagnostic biomarkers and novel vaccine targets. As translational tools they can facilitate testing of candidate vaccines and drugs and evaluation of diagnostic tests.

AREAS COVERED

Until recently, malaria human challenge models have been limited to only a few Plasmodium falciparum strains and used exclusively in malaria-naïve volunteers in non-endemic regions. Several recent advances include the use of alternate P. falciparum strains and other species of Plasmodia, as well as strains attenuated by chemical, radiation or genetic modification, and the conduct of studies in pre-exposed individuals. Herein, we discuss how this diversification is enabling more thorough vaccine efficacy testing and informing rational vaccine development.

EXPERT OPINION

The ability to comprehensively evaluate vaccine efficacy in controlled settings will continue to accelerate the translation of candidate malaria vaccines to the clinic, and inform the development and optimisation of potential vaccines that would be effective against multiple strains in geographically and demographically diverse settings.

Plasmodium falciparum artemisinin resistance monitoring in Sabah, Malaysia: in vivo therapeutic efficacy and kelch13 molecular marker surveillance

BACKGROUND

Spreading Plasmodium falciparum artemisinin drug resistance threatens global malaria public health gains. Limited data exist to define the extent of P. falciparum artemisinin resistance southeast of the Greater Mekong region in Malaysia.

METHODS

A clinical efficacy study of oral artesunate (total target dose 12 mg/kg) daily for 3 days was conducted in patients with uncomplicated falciparum malaria and a parasite count < 100,000/µL admitted to 3 adjacent district hospitals in Sabah, East Malaysia. On day 3 and 4 all patients were administered split dose mefloquine (total dose 25 mg/kg) and followed for 28 days. Twenty-one kelch13 polymorphisms associated with P. falciparum artemisinin resistance were also evaluated in P. falciparum isolates collected from patients presenting to health facilities predominantly within the tertiary referral area of western Sabah between 2012 and 2016.

RESULTS

In total, 49 patients were enrolled and treated with oral artesunate. 90% (44/49) of patients had cleared their parasitaemia by 48 h and 100% (49/49) within 72 h. The geometric mean parasite count at presentation was 9463/µL (95% CI 6757-13,254), with a median time to 50% parasite clearance of 4.3 h (IQR 2.0-8.4). There were 3/45 (7%) patients with a parasite clearance slope half-life of ≥ 5 h. All 278 P. falciparum isolates evaluated were wild-type for kelch13 markers.

CONCLUSION

There is no suspected or confirmed evidence of endemic artemisinin-resistant P. falciparum in this pre-elimination setting in Sabah, Malaysia. Current guidelines recommending first-line treatment with ACT remain appropriate for uncomplicated malaria in Sabah, Malaysia. Ongoing surveillance is needed southeast of the Greater Mekong sub-region.

Plasmodium knowlesi malaria: current research perspectives

Originally known to cause simian malaria, Plasmodium knowlesi is now known as the fifth human malaria species. Since the publishing of a report that largely focused on human knowlesi cases in Sarawak in 2004, many more human cases have been reported in nearly all of the countries in Southeast Asia and in travelers returning from these countries. The zoonotic nature of this infection hinders malaria elimination efforts. In order to grasp the current perspective of knowlesi malaria, this literature review explores the different aspects of the disease including risk factors, diagnosis, treatment, and molecular and functional studies. Current studies do not provide sufficient data for an effective control program. Therefore, future direction for knowlesi research is highlighted here with a final aim of controlling, if not eliminating, the parasite.

Age-Related Clinical Spectrum of Plasmodium knowlesi Malaria and Predictors of Severity

Background

Plasmodium knowlesi is increasingly reported in Southeast Asia, but prospective studies of its clinical spectrum in children and comparison with autochthonous human-only Plasmodium species are lacking.

Methods

Over 3.5 years, we prospectively assessed patients of any age with molecularly-confirmed Plasmodium monoinfection presenting to 3 district hospitals in Sabah, Malaysia.

Results

Of 481 knowlesi, 172 vivax, and 96 falciparum malaria cases enrolled, 44 (9%), 71 (41%), and 31 (32%) children aged ≤12 years. Median parasitemia was lower in knowlesi malaria (2480/μL [interquartile range, 538-8481/μL]) than in falciparum (9600/μL; P < .001) and vivax malaria. In P. knowlesi, World Health Organization-defined anemia was present in 82% (95% confidence interval [CI], 67%-92%) of children vs 36% (95% CI, 31%-41%) of adults. Severe knowlesi malaria occurred in 6.4% (95% CI, 3.9%-8.3%) of adults but not in children; the commenst severity criterion was acute kideny injury. No patient had coma. Age, parasitemia, schizont proportion, abdominal pain, and dyspnea were independently associated with severe knowlesi malaria, with parasitemia >15000/μL the best predictor (adjusted odds ratio, 16.1; negative predictive value, 98.5%; P < .001). Two knowlesi-related adult deaths occurred (fatality rate: 4.2/1000 adults).

Conclusions

Age distribution and parasitemia differed markedly in knowlesi malaria compared to human-only species, with both uncomplicated and severe disease occurring at low parasitemia. Severe knowlesi malaria occurred only in adults; however, anemia was more common in children despite lower parasitemia. Parasitemia independently predicted knowlesi disease severity: Intravenous artesunate is warranted initially for those with parasitemia >15000/μL.