Antimalarial Drug Resistance: A Threat to Malaria Elimination

Establishment and evaluation of a qPCR method for the detection of pfmdr1 mutations in Plasmodium falciparum, the causal agent of fatal malaria

Drug resistance surveillance is a major integral part of malaria control programs. Molecular methods play a pivotal role in drug resistance detection and related molecular research. This study aimed to develop a rapid and accurate detection method for drug resistance of Plasmodium falciparum (P. falciparum). A quantitative real-time PCR (qPCR) assay has been developed that identifies the mutation at locus A256T in the P.falciparum multi-drug resistance(pfmdr1) gene producing amino acid change at position 86. The results of 198 samples detected by qPCR were consistent with nested PCR and sequencing, giving an accuracy of 94.3%. The sensitivity, specificity, positive and negative predictive value of qPCR were 85.7%, 97.6%, 90.0% and 96.4%, respectively. The results of qPCR are basically consistent with the nested PCR, which is expected to replace the nested PCR as a new molecular biological method for drug resistance detection, providing reliable technical support for global malaria prevention and control.

The dichotomy between probiotic lactic acid bacteria and Plasmodium: A promising therapeutic avenue

Our understanding of gut microbial populations and their immense influence on host immunity, health, and diseases has increased deeply in recent years. Numerous reports have identified the role of mosquito and mammalian gut microbiota in the modulation of host susceptibility to Plasmodium infection. Artemisinin resistance in malaria-endemic regions necessitates the development of new, safer, and more affordable treatments to supplement existing therapies. In this review, we compiled a colossal amount of data from numerous studies that have assessed the roles played by gut microbial communities in Plasmodium infection, progression, transmission, and severity. Most interestingly, our study points to the overwhelming evidence from experimental studies in mural malaria to human trials, suggesting that the presence of lactic acid bacteria in the gut microbiota of mammalian hosts provides a great degree of protection against malaria. Therefore, our study provides a compelling narrative for probiotic administration as an adjunct therapy for combatting malaria.

Mutations in Plasmodium falciparum Kelch13 (PfK13) dysregulates PI3K/AKT signalling pathway in artemisinin resistance

BACKGROUND

PfK13 protein mutations are associated with the emergence of artemisinin resistance in Plasmodium falciparum. PfK13 protein is essential for mediating ubiquitination and controlling the PI3K/AKT pathway. Mutant PfK13 variations can interfere with substrate binding, especially with PfPI3K, which raises PfPI3K levels.

METHODS

DUET, DynaMut2, mCSM, iStable 2.0, I-Mutant 2.0, and MuPro were utilized to study the protein stability and protein-substrate binding was studied using HADDOCK 2.4 docking algorithm between Wild-type and mutant PfK13 with the helical and catalytic domain of PfPI3K.

RESULTS

i-Stable server analysis predicted that seven, out of the nine mutations associated with artemisinin resistance (F446I, Y493H, R539T, I543T, P553L, R561H, C580Y) reduced the protein stability. HADDOCK scores of the catalytic domain underscores the significant impact of the reported mutations on the binding affinity of the PfK13 protein. Further validation through the MM_GBSA technique, the binding free energy (DDG) between the wild-type and the mutant PfK13 protein analysis revealed a loss of interactions resulting from mutations in PfK13.

CONCLUSION

The study finding suggest that mutations in the PfK13 cause destabilization in the protein structure and affects the binding of PfPI3K. Although the findings remain preliminary and require further validation, it provides the basis for further research considering the importance of the interaction of PfK13 and PfPI3K to overcome the impact of artemisinin resistance.

An overview of artemisinin-resistant malaria and associated Pfk13 gene mutations in Central Africa

Malaria caused by Plasmodium falciparum is one of the deadliest and most common tropical infectious diseases. However, the emergence of artemisinin drug resistance associated with the parasite's Pfk13 gene, threatens the public health of individual countries as well as current efforts to reduce malaria burdens globally. It is of concern that artemisinin-resistant parasites may be selected or have already emerged in Africa. This narrative review aims to evaluate the published evidence concerning validated, candidate, and novel Pfk13 polymorphisms in ten Central African countries. Results show that four validated non-synonymous polymorphisms (M476I, R539T, P553L, and P574L), directly associated with a delayed therapy response, have been reported in the region. Also, two Pfk13 polymorphisms associated to artemisinin resistance but not validated (C469F and P527H) have been reported. Furthermore, several non-validated mutations have been observed in Central Africa, and one allele A578S, is commonly found in different countries, although additional molecular and biochemical studies are needed to investigate whether those mutations alter artemisinin effects. This information is discussed in the context of biochemical and genetic aspects of Pfk13, and related to the regional malaria epidemiology of Central African countries.

In vitro, in vivo and in silico antiplasmodial profiling of the aqueous extract of Hibiscus asper HOOK F. Leaf (Malvaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Plasmodium resistance to antimalarial drugs raises the urgent need to seek for alternative treatments. Aqueous extract of Hibiscus asper leaves is currently used in malaria management but remains less documented.

AIM OF THE STUDY

The study aims to evaluate antimalarial effects of the aqueous extract of Hibiscus asper. UHPLC/MS, was used to identify some likely compounds present in the plant that were thereafter docked to some malaria parasite proteins.

STUDY DESIGN

In vitro anti-plasmodium and antioxidant, UHPLC/Ms analysis, in vivo antimalarial of the plant extract, and in silico molecular docking prediction of some identified compounds were performed to investigate the pharmacological effects of H. asper.

MATERIAL AND METHODS

The in vitro antiplasmodial activity of the extract was carried out on Plasmodium falciparum strains using SYBR-green dye; then, the curative antimalarial activity was conducted on Plasmodium berghei NK65-infected male Wistar rats. The UHPLC/MS analysis was used to identify plant compounds, followed by interactions (docking affinity) between some compounds and parasitic enzymes such as P. falciparum purine nucleoside phosphorylase (2BSX) and 6-phosphogluconate dehydrogenase (6FQY) to explore potential mechanisms of action at the molecular level.

RESULTS

No hemolysis effect of the extract was observed at concentrations up to 100 mg/mL. In vitro test of the aqueous leaves extract of H. asper showed inhibitory activity against P. falciparum Dd2 and 3D7 strains with IC50 values of 19.75 and 21.97 μg/mL, respectively. The curative antimalarial test of the H. asper extract in infected rats exhibited significant inhibition of the parasite growth (p < 0.001) with inhibition percentage of 95.11%, 97.68% and 95.59% at all the doses (50, 100 and 200 mg/kg) respectively. The extract corrected major physiological alterations such as liver and kidney impairments, oxidative stress and architectural disorganization in liver, spleen and kidneys tissues. The UHPLC/MS analysis identified 7 compounds, namely chlorogenic acid, azulene, quercetin, rhodine, 1-ethyl-2,4-dimethyl benzene and phthalan. Out of seven compounds identified in the extract quercetin and phthalan showed higher in silico inhibitory activity against P. falciparum purine nucleoside phosphorylase and Plasmodium falciparum 6-phosphosgluconate dehydrogenase parasite enzymes.

CONCLUSION

These findings indicate that H. asper could be a promising complementary medicine to manage malaria. Meanwhile, the affinity of annoted compounds with these enzymes should be further confirmed.

DNA sequence and chromatin differentiate sequence-specific transcription factor binding in the human malaria parasite Plasmodium falciparum

Development of the malaria parasite, Plasmodium falciparum, is regulated by a limited number of sequence-specific transcription factors (TFs). However, the mechanisms by which these TFs recognize genome-wide binding sites is largely unknown. To address TF specificity, we investigated the binding of two TF subsets that either bind CACACA or GTGCAC DNA sequence motifs and further characterized two additional ApiAP2 TFs, PfAP2-G and PfAP2-EXP, which bind unique DNA motifs (GTAC and TGCATGCA). We also interrogated the impact of DNA sequence and chromatin context on P. falciparum TF binding by integrating high-throughput in vitro and in vivo binding assays, DNA shape predictions, epigenetic post-translational modifications, and chromatin accessibility. We found that DNA sequence context minimally impacts binding site selection for paralogous CACACA-binding TFs, while chromatin accessibility, epigenetic patterns, co-factor recruitment, and dimerization correlate with differential binding. In contrast, GTGCAC-binding TFs prefer different DNA sequence context in addition to chromatin dynamics. Finally, we determined that TFs that preferentially bind divergent DNA motifs may bind overlapping genomic regions due to low-affinity binding to other sequence motifs. Our results demonstrate that TF binding site selection relies on a combination of DNA sequence and chromatin features, thereby contributing to the complexity of P. falciparum gene regulatory mechanisms.

Compound management in a virtual research organization: The cornerstone of a reliable MMV discovery engine

Despite the efforts towards malaria eradication, latest estimates show that the number of malaria cases is still rising, and malaria continues to have a devastating impact on people's health and livelihoods particularly in populations located in sub-Saharan Africa 1. As a Product Development Partnership (PDP), MMV Medicines for Malaria Venture (MMV) plays a crucial role by using public and philanthropic funds to engage the pharmaceutical industry and academic research institutions to discover, develop and deliver the new drugs needed to control and eradicate malaria. MMV Discovery, working with partners, has developed a robust pipeline of molecules and a reliable discovery engine able to support research projects from screening to candidate nomination, providing access to centers of expertise and evaluating the profile and potential of molecules. To efficiently support this malaria discovery effort, MMV and its partners have established a state-of-the-art compound management network, supporting all discovery activities. This network serves both discovery projects and open innovation initiatives, such as MMV Open, tailoring workflows to align with distinct project objectives. In addition to this, MMV has implemented reliable integrated logistic tools and interfaces. These tools enable the efficient management and tracking of individual not solubilized (dry) samples of project compounds, as well as dedicated, solubilized libraries of compounds designated for primary screens targeting malaria and other neglected diseases.

Elevated Inflammation Associated with Markers of Neutrophil Function and Gastrointestinal Disruption in Pilot Study of Plasmodium fragile Co-Infection of ART-Treated SIVmac239+ Rhesus Macaques

Human immunodeficiency virus (HIV) and malaria, caused by infection with Plasmodium spp., are endemic in similar geographical locations. As a result, there is high potential for HIV/Plasmodium co-infection, which increases the pathology of both diseases. However, the immunological mechanisms underlying the exacerbated disease pathology observed in co-infected individuals are poorly understood. Moreover, there is limited data available on the impact of Plasmodium co-infection on antiretroviral (ART)-treated HIV infection. Here, we used the rhesus macaque (RM) model to conduct a pilot study to establish a model of Plasmodium fragile co-infection during ART-treated simian immunodeficiency virus (SIV) infection, and to begin to characterize the immunopathogenic effect of co-infection in the context of ART. We observed that P. fragile co-infection resulted in parasitemia and anemia, as well as persistently detectable viral loads (VLs) and decreased absolute CD4+ T-cell counts despite daily ART treatment. Notably, P. fragile co-infection was associated with increased levels of inflammatory cytokines, including monocyte chemoattractant protein 1 (MCP-1). P. fragile co-infection was also associated with increased levels of neutrophil elastase, a plasma marker of neutrophil extracellular trap (NET) formation, but significant decreases in markers of neutrophil degranulation, potentially indicating a shift in the neutrophil functionality during co-infection. Finally, we characterized the levels of plasma markers of gastrointestinal (GI) barrier permeability and microbial translocation and observed significant correlations between indicators of GI dysfunction, clinical markers of SIV and Plasmodium infection, and neutrophil frequency and function. Taken together, these pilot data verify the utility of using the RM model to examine ART-treated SIV/P. fragile co-infection, and indicate that neutrophil-driven inflammation and GI dysfunction may underlie heightened SIV/P. fragile co-infection pathogenesis.

Increased sensitivity of malaria parasites to common antimalaria drugs after the introduction of artemether-lumefantrine: Implication of policy change and implementation of more effective drugs in fight against malaria

Single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum multi-drug resistance protein 1 (Pfmrp1) gene have previously been reported to confer resistance to Artemisinin-based Combination Therapies (ACTs) in Southeast Asia. A total of 300 samples collected from six sites between 2008 and 2019 under an ongoing malaria drug sensitivity patterns in Kenya study were evaluated for the presence of SNPs at Pfmrp1 gene codons: H191Y, S437A, I876V, and F1390I using the Agena MassARRAY® platform. Each isolate was further tested against artemisinin (ART), lumefantrine (LU), amodiaquine (AQ), mefloquine (MQ), quinine (QN), and chloroquine (CQ) using malaria the SYBR Green I-based method to determine their in vitro drug sensitivity. Of the samples genotyped, polymorphism at Pfmrp1 codon I876V was the most frequent, with 59.3% (163/275) mutants, followed by F1390I, 7.2% (20/278), H191Y, 4.0% (6/151), and S437A, 3.3% (9/274). A significant decrease in median 50% inhibition concentrations (IC50s) and interquartile range (IQR) was noted; AQ from 2.996 ng/ml [IQR = 2.604-4.747, n = 51] in 2008 to 1.495 ng/ml [IQR = 0.7134-3.318, n = 40] (P<0.001) in 2019, QN from 59.64 ng/ml [IQR = 29.88-80.89, n = 51] in 2008 to 18.10 ng/ml [IQR = 11.81-26.92, n = 42] (P<0.001) in 2019, CQ from 35.19 ng/ml [IQR = 16.99-71.20, n = 30] in 2008 to 6.699 ng/ml [IQR = 4.976-9.875, n = 37] (P<0.001) in 2019, and ART from 2.680 ng/ml [IQR = 1.608-4.857, n = 57] in 2008 to 2.105 ng/ml [IQR = 1.266-3.267, n = 47] (P = 0.0012) in 2019, implying increasing parasite sensitivity to the drugs over time. However, no significant variations were observed in LU (P = 0.2692) and MQ (P = 0.0939) respectively, suggesting stable parasite responses over time. There was no statistical significance between the mutation at 876 and parasite sensitivity to selected antimalarials tested, suggesting stable sensitivity for the parasites with 876V mutations. These findings show that Kenyan parasite strains are still sensitive to AQ, QN, CQ, ART, LU, and MQ. Despite the presence of Pfmrp1 mutations in parasites among the population.

Impact of different mutations on Kelch13 protein levels, ART resistance, and fitness cost in Plasmodium falciparum parasites

Reduced susceptibility to ART, the first-line treatment against malaria, is common in South East Asia (SEA). It is associated with point mutations, mostly in kelch13 (k13) but also in other genes, like ubp1. K13 and its compartment neighbors (KICs), including UBP1, are involved in endocytosis of host cell cytosol. We tested 135 mutations in KICs but none conferred ART resistance. Double mutations of k13C580Y with k13R539T or k13C580Y with ubp1R3138H, did also not increase resistance. In contrast, k13C580Y parasites subjected to consecutive RSAs did, but the k13 sequence was not altered. Using isogenic parasites with different k13 mutations, we found correlations between K13 protein amount, resistance, and fitness cost. Titration of K13 and KIC7 indicated that the cellular levels of these proteins determined resistance through the rate of endocytosis. While fitness cost of k13 mutations correlated with ART resistance, ubp1R3138H caused a disproportionately higher fitness cost.

IMPORTANCE

Parasites with lowered sensitivity to artemisinin-based drugs are becoming widespread. However, even in these "resistant" parasites not all parasites survive treatment. We found that the proportion of surviving parasites correlates with the fitness cost of resistance-inducing mutations which might indicate that the growth disadvantages prevents resistance levels where all parasites survive treatment. We also found that combining two common resistance mutations did not increase resistance levels. However, selection through repeated ART-exposure did, even-though the known resistance genes, including k13, were not further altered, suggesting other causes of increased resistance. We also observed a disproportionally high fitness cost of a resistance mutation in resistance gene ubp1. Such high fitness costs may explain why mutations in ubp1 and other genes functioning in the same pathway as k13 are rare. This highlights that k13 mutations are unique in their ability to cause resistance at a comparably low fitness cost.

Acetyl-CoA Synthetase Mutations S868G and V949I Do Not Confer Resistance to Antimalarial Drugs in vitro in Plasmodium falciparum

Plasmodium falciparum acetyl-CoA synthetase (PfACAS) protein is an important source of acetyl-CoA. We detected the mutations S868G and V949I in PfACAS by whole-genome sequencing analysis in some recrudescent parasites after antimalarial treatment with artesunate and dihydroartemisinin-piperaquine, suggesting that they may confer drug resistance. Using CRISPR/Cas9 technology, we engineered parasite lines carrying the PfACAS S868G and V949I mutations in two genetic backgrounds and evaluated their susceptibility to antimalarial drugs in vitro. The results demonstrated that PfACAS S868G and V949I mutations alone or in combination were not enough to provide resistance to antimalarial drugs.

Curing mosquitoes with genetic approaches for malaria control

Malaria remains a persistent global public health challenge because of the limitations of current prevention tools. The use of transgenic mosquitoes incapable of transmitting malaria, in conjunction with existing methods, holds promise for achieving elimination of malaria and preventing its reintroduction. In this context, population modification involves the spread of engineered genetic elements through mosquito populations that render them incapable of malaria transmission. Significant progress has been made in this field over the past decade in revealing promising targets, optimizing genetic tools, and facilitating the transition from the laboratory to successful field deployments, which are subject to regulatory scrutiny. This review summarizes recent advances and ongoing challenges in 'curing' Anopheles vectors of the malaria parasite.

Advancing liposome technology for innovative strategies against malaria

This review discusses the potential of liposomes as drug delivery systems for antimalarial therapies. Malaria continues to be a significant cause of mortality and morbidity, particularly among children and pregnant women. Drug resistance due to patient non-compliance and troublesome side effects remains a significant challenge in antimalarial treatment. Liposomes, as targeted and efficient drug carriers, have garnered attention owing to their ability to address these issues. Liposomes encapsulate hydrophilic and/or hydrophobic drugs, thus providing comprehensive and suitable therapeutic drug delivery. Moreover, the potential of passive and active drug delivery enables drug concentration in specific target tissues while reducing adverse effects. However, successful liposome formulation is influenced by various factors, including drug physicochemical characteristics and physiological barriers encountered during drug delivery. To overcome these challenges, researchers have explored modifications in liposome nanocarriers to achieve efficient drug loading, controlled release, and system stability. Computational approaches have also been adopted to predict liposome system stability, membrane integrity, and drug-liposome interactions, improving formulation development efficiency. By leveraging computational methods, optimizing liposomal drug delivery systems holds promise for enhancing treatment efficacy and minimizing side effects in malaria therapy. This review consolidates the current understanding and highlights the potential of liposome strategies against malaria.

Anti-inflammatory and immunomodulatory effects of mesenchymal stem cell therapy on parasitic drug resistance

INTRODUCTION

The emergence of antiparasitic drug resistance poses a concerning threat to animals and humans. Mesenchymal Stem Cells (MSCs) have been widely used to treat infections in humans, pets, and livestock. Although this is an emerging field of study, the current review outlines possible mechanisms and examines potential synergism in combination therapies and the possible harmful effects of such an approach.

AREAS COVERED

The present study delved into the latest pre-clinical research on utilizing MSCs to treat parasitic infections. As per investigations, the introduction of MSCs to patients grappling with parasitic diseases like schistosomiasis, malaria, cystic echinococcosis, toxoplasmosis, leishmaniasis, and trypanosomiasis has shown a reduction in parasite prevalence. This intervention also alters the levels of both pro- and anti-inflammatory cytokines. Furthermore, the combined administration of MSCs and antiparasitic drugs has demonstrated enhanced efficacy in combating parasites and modulating the immune response.

EXPERT OPINION

Mesenchymal stem cells are a potential solution for addressing parasitic drug resistance. This is mainly because of their remarkable immunomodulatory abilities, which can potentially help combat parasites' resistance to drugs.

Ten-year trend analysis of malaria prevalence in Gindabarat district, West Shawa Zone, Oromia Regional State, Western Ethiopia

BACKGROUND

Malaria is a major public health concern in Ethiopia, where more than half of the population lives in malaria risk areas. While several studies have been conducted in different eco-epidemiological settings in Ethiopia, there is a notable scarcity of data on the prevalence of malaria in the Gindabarat district. Therefore, this study aimed to analyse 10-year trend of malaria prevalence in Gindabarat district, West Shawa Zone of Oromia, Western Ethiopia.

METHODS

A retrospective laboratory record review was conducted at Gindabarat General Hospital and Gindabarat District Health Office from September 2011 to August 2020. The retrieved data included the date of examination, age, sex and laboratory results of the blood smears, including the Plasmodium species identified. Data were summarized and presented in the form of tables, figures, and frequencies to present the results. The data were analysed using SPSS (version 25.0) and Microsoft Excel.

RESULTS

Over the course of 10 years, a total of 11,478 blood smears were examined in the public health facilities in the district. Of the total blood smears examined, 1372 (11.95%) were microscopically confirmed malaria. Plasmodium falciparum, Plasmodium vivax and mixed infections (P. falciparum and P. vivax) accounted for 70.77%, 20.55% and 8.67% of the cases, respectively. Malaria prevalence was significantly higher among individuals aged ≥ 15 years (12.60%, x2 = 13.6, df = 2, p = 0.001) and males (14.21%, x2 = 59.7, df = 1, p = 0.001). The highest number of malaria cases was recorded from September to November.

CONCLUSION

Malaria remains a public health problem in the district. P. falciparum was the most predominant parasite species in the area. Malaria prevalence was significantly higher among individuals aged ≥ 15 years and males. There was a remarkable fluctuation in the number of malaria cases in different months and years. In the study area malaria cases peaked in 2015 and 2017 then decreasing from 2017 to 2019, with sharp increase in 2020. Moreover, this study showed malaria cases were reported in all seasons and months, but the highest was observed from September to November. Strengthening malaria control activities is essential to further reduce the burden of malaria and pave the way for the anticipated elimination.

Genome Analysis of Plasmodium falciparum: A Preliminary Observation - Sierra Leone, 2022-2023

What is already known about this topic?

Sierra Leone, with a gross domestic product (GDP) per capita below $300 and significant poverty, ranks among the world's least developed countries (LDCs). Despite its modest population of 8.6 million, the nation reports approximately 2.6 million malaria cases annually. Previously, there has been no reporting on the malaria genome data from this country.

What is added by this report?

In this study, we present the first reported whole-genome sequence analysis of 19 high parasite-density Plasmodium falciparum isolates from Sierra Leone, providing insights into the genomic epidemiology of this high-prevalence area. We found a high degree of relatedness among infections and substantial genetic diversity, consistent with the gradual reduction in overall case numbers. Moreover, our whole-genome analysis revealed that, beyond drug-resistance genes, gene families related to blood cell invasion, immune evasion, and others are undergoing directional selection. This suggests that the population in Sierra Leone has developed a relatively strong acquired immunity.

What are the implications for public health practice?

The genomic data not only facilitate the creation of single nucleotide polymorphism barcodes for case tracking but also enable the analysis of evolving transmission dynamics and selection pressures. Additionally, the samples from Sierra Leone exhibited higher selective pressures on resistance genes compared to those from Asia, a trend not commonly observed in other African samples. This suggests that less stringent healthcare systems and inconsistent treatment strategies can subject parasites to increased drug pressure, thereby accelerating the development of resistant strains.

Plasmodium falciparum Alba6 exhibits DNase activity and participates in stress response

Alba domain proteins, owing to their functional plasticity, play a significant role in organisms. Here, we report an intrinsic DNase activity of PfAlba6 from Plasmodium falciparum, an etiological agent responsible for human malignant malaria. We identified that tyrosine28 plays a critical role in the Mg2+ driven 5'-3' DNase activity of PfAlba6. PfAlba6 cleaves both dsDNA as well as ssDNA. We also characterized PfAlba6-DNA interaction and observed concentration-dependent oligomerization in the presence of DNA, which is evident from size exclusion chromatography and single molecule AFM-imaging. PfAlba6 mRNA expression level is up-regulated several folds following heat stress and treatment with artemisinin, indicating a possible role in stress response. PfAlba6 has no human orthologs and is expressed in all intra-erythrocytic stages; thus, this protein can potentially be a new anti-malarial drug target.

Sanger sequencing and deconvolution of polyclonal infections: a quantitative approach to monitor drug-resistant Plasmodium falciparum

BACKGROUND

Anti-malarial drug resistance in Plasmodium falciparum is a major public health problem in malaria-endemic regions. Although various technical improvements in sequencing methods have been introduced to identify SNPs, the conventional approach with current tools does not discriminate mixed infections, and thus can be improved for more sensitive surveillance of anti-malarial resistance to better inform control strategies.

METHODS

We developed a computational approach for deconvolution of chromatograms generated by standard Sanger sequencing of PCR amplicons in order to quantify molecular marker variants of anti-malarial drug resistance genes [Plasmodium falciparum dihydropteorate synthase (Pfdhps) and P. falciparum dihydrofolate reductase (Pfdhfr)]. We validated this computational approach using mixtures of V1/S and FCR3 at varying proportions between 0 and 100%, then applied it to field samples collected in Doneguebougou, Mali in 2018. We determined the mean fraction of resistance alleles in individual samples, as well as the prevalence of infections carrying resistant parasites.

FINDINGS

We observed a highly significant correlation between the predicted and measured proportions of V1/S and FCR3 alleles in mixed laboratory samples (all p < 0.001). Among field samples, the mean fraction of resistant Pfdhps alleles was 4.7% 431V, 95.9% 436F/A, 49.9% 437G, 0.0% 540E, 1.2% 581G and 1.5% 613S/T; corresponding prevalences were 50.0%, 100%, 72.5%, 0.0%, 25.0%, and 12.5%, respectively. The mean fraction of resistant Pfdhfr alleles was 0.6% 16V, 11.1% 50R, 89.0% 51I, 98.3% 59R, 74.7% 108T/N, 8.6% 140L and 8.7% 164L; corresponding prevalences were 12.5%, 75.0%, 100%, 100%, 100%, 50.0%, and 28.6%, respectively. We identified two new point mutations on the Pfdhps gene at codons D484T and D545N.

INTERPRETATION

Computational deconvolution of sequencing chromatograms can discriminate varying proportions of antimalarial drug-sensitive versus -resistant alleles. This cost-effective and quantitative variant-sequencing approach will be useful for population-based surveys that characterize mixed infections at the individual level to survey known and unknown mutations in P. falciparum drug-resistance genes.

FUNDING

This work was supported by the Division of Intramural Research of the National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH). HM was supported by the African Postdoctoral Training Initiative (APTI) Fellowship program jointly managed by the US NIH, The African Academy of Sciences (AAS) and Bill & Melinda Gates Foundation (BMGF); Grant Reference Number: APTI-18-01.

Efficacy of artemether-lumefantrine and dihydroartemisinin-piperaquine and prevalence of molecular markers of anti-malarial drug resistance in children in Togo in 2021

BACKGROUND

Artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DP) are the currently recommended first- and second-line therapies for uncomplicated Plasmodium falciparum infections in Togo. This study assessed the efficacy of these combinations, the proportion of Day3-positive patients (D3 +), the proportion of molecular markers associated with P. falciparum resistance to anti-malarial drugs, and the variable performance of HRP2-based malaria rapid diagnostic tests (RDTs).

METHODS

A single arm prospective study evaluating the efficacy of AL and DP was conducted at two sites (Kouvé and Anié) from September 2021 to January 2022. Eligible children were enrolled, randomly assigned to treatment at each site and followed up for 42 days after treatment initiation. The primary endpoint was polymerase chain reaction (PCR) adjusted adequate clinical and parasitological response (ACPR). At day 0, samples were analysed for mutations in the Pfkelch13, Pfcrt, Pfmdr-1, dhfr, dhps, and deletions in the hrp2/hrp3 genes.

RESULTS

A total of 179 and 178 children were included in the AL and DP groups, respectively. After PCR correction, cure rates of patients treated with AL were 97.5% (91.4-99.7) at day 28 in Kouvé and 98.6% (92.4-100) in Anié, whereas 96.4% (CI 95%: 89.1-98.8) and 97.3% (CI 95%: 89.5-99.3) were observed at day 42 in Kouvé and Anié, respectively. The cure rates of patients treated with DP at day 42 were 98.9% (CI 95%: 92.1-99.8) in Kouvé and 100% in Anié. The proportion of patients with parasites on day 3 (D3 +) was 8.5% in AL and 2.6% in DP groups in Anié and 4.3% in AL and 2.1% DP groups in Kouvé. Of the 357 day 0 samples, 99.2% carried the Pfkelch13 wild-type allele. Two isolates carried nonsynonymous mutations not known to be associated with artemisinin partial resistance (ART-R) (A578S and A557S). Most samples carried the Pfcrt wild-type allele (97.2%). The most common Pfmdr-1 allele was the single mutant 184F (75.6%). Among dhfr/dhps mutations, the quintuple mutant haplotype N51I/C59R/S108N + 437G/540E, which is responsible for SP treatment failure in adults and children, was not detected. Single deletions in hrp2 and hrp3 genes were detected in 1/357 (0.3%) and 1/357 (0.3%), respectively. Dual hrp2/hrp3 deletions, which could affect the performances of HRP2-based RDTs, were not observed.

CONCLUSION

The results of this study confirm that the AL and DP treatments are highly effective. The absence of the validated Pfkelch13 mutants in the study areas suggests the absence of ART -R, although a significant proportion of D3 + cases were found. The absence of dhfr/dhps quintuple or sextuple mutants (quintuple + 581G) supports the continued use of SP for IPTp during pregnancy and in combination with amodiaquine for seasonal malaria chemoprevention.

TRIAL REGISTRATION

ACTRN12623000344695.

Prevalence of unqualified sources of antimalarial drug prescription for children under the age of five: A study in 19 low- and middle-income countries

BACKGROUND

Antimalarial drug resistance poses a severe danger to global health. In Low- and Middle-Income Countries (LMICs), there is a lack of reliable information on antimalarial prescriptions for recent malarial fever in children under five. Our study aims to determine the prevalence of unqualified sources of antimalarial drug prescription for children under the age of five in 19 low- and middle-income countries.

METHODS

We performed a cross-sectional study of the Malaria Indicator Survey (MIS) datasets (n = 106265) across 19 LMICs. The recent MIS datasets were used, and the study only included children under five who had taken an antimalarial drug for a recent malarial fever. The outcome variable was classified into two distinct categories: those who had taken antimalarial drugs for malarial fever from qualified sources and those who did not.

FINDINGS

Among LMICs, we found that 87.1% of children under five received an antimalarial prescription from unqualified sources who had recently experienced malarial fever. In several LMICs (Tanzania, Nigeria, and Ghana), a substantial portion of recent antimalarial prescriptions for malaria was taken from unqualified sources (about 60%). Some LMICs (Guinea (31.8%), Mali (31.3%), Nigeria (20.4%), Kenya (2.6%), and Senegal (2.7%)) had low rates of antimalarial drug consumption even though children under five received a high percentage of antimalarial prescriptions from qualified sources for a recent malarial fever. Living in rural areas, having mothers with higher education, and having parents with more wealth were frequently taken antimalarial from qualified sources for recent malarial fever in children under five across the LMICs.

INTERPRETATION

The study draws attention to the importance of national and local level preventative strategies across the LMICs to restrict antimalarial drug consumption. This is because antimalarial prescriptions from unqualified sources for recent malarial fever in children under five were shockingly high in most LMICs and had high rates of unqualified prescriptions in certain other LMICs.

A History of Malaria and Conflict

It is supposed that in all armed conflicts until World War II more humans died of infectious diseases than of the actual violence. Especially malaria left a crucial imprint on wars throughout history. The disease aggravates wartime conditions, is thus responsible for significant morbidity and mortality in conflict zones, and is at the same time more commonly found in these areas. Malaria has halted many military campaigns in the past, with prominent examples ranging from antiquity through the medieval period and into the modern era. The parasitosis still continues to play an important role in the outcome of warfare and follow-up events today and is of special public health importance in areas of the Global South, where most of its endemicity and some of the most brutal conflicts of our time are located. Vice versa, wars and ensuing population movements increase malaria transmission and morbidity as well as impede control efforts. Awareness of this and the development of strategies to overcome both malaria and wars will massively improve the well-being of the population affected.

Inhibition of malaria and babesiosis parasites by putative red blood cell targeting small molecules

Background

Chemotherapies for malaria and babesiosis frequently succumb to the emergence of pathogen-related drug-resistance. Host-targeted therapies are thought to be less susceptible to resistance but are seldom considered for treatment of these diseases.

Methods

Our overall objective was to systematically assess small molecules for host cell-targeting activity to restrict proliferation of intracellular parasites. We carried out a literature survey to identify small molecules annotated for host factors implicated in Plasmodium falciparum infection. Alongside P. falciparum, we implemented in vitro parasite susceptibility assays also in the zoonotic parasite Plasmodium knowlesi and the veterinary parasite Babesia divergens. We additionally carried out assays to test directly for action on RBCs apart from the parasites. To distinguish specific host-targeting antiparasitic activity from erythrotoxicity, we measured phosphatidylserine exposure and hemolysis stimulated by small molecules in uninfected RBCs.

Results

We identified diverse RBC target-annotated inhibitors with Plasmodium-specific, Babesia-specific, and broad-spectrum antiparasitic activity. The anticancer MEK-targeting drug trametinib is shown here to act with submicromolar activity to block proliferation of Plasmodium spp. in RBCs. Some inhibitors exhibit antimalarial activity with transient exposure to RBCs prior to infection with parasites, providing evidence for host-targeting activity distinct from direct inhibition of the parasite.

Conclusions

We report here characterization of small molecules for antiproliferative and host cell-targeting activity for malaria and babesiosis parasites. This resource is relevant for assessment of physiological RBC-parasite interactions and may inform drug development and repurposing efforts.

Frequency-dependent ecological interactions increase the prevalence, and shape the distribution, of pre-existing drug resistance

The evolution of resistance remains one of the primary challenges for modern medicine from infectious diseases to cancers. Many of these resistance-conferring mutations often carry a substantial fitness cost in the absence of treatment. As a result, we would expect these mutants to undergo purifying selection and be rapidly driven to extinction. Nevertheless, pre-existing resistance is frequently observed from drug-resistant malaria to targeted cancer therapies in non-small cell lung cancer (NSCLC) and melanoma. Solutions to this apparent paradox have taken several forms from spatial rescue to simple mutation supply arguments. Recently, in an evolved resistant NSCLC cell line, we found that frequency-dependent ecological interactions between ancestor and resistant mutant ameliorate the cost of resistance in the absence of treatment. Here, we hypothesize that frequency-dependent ecological interactions in general play a major role in the prevalence of pre-existing resistance. We combine numerical simulations with robust analytical approximations to provide a rigorous mathematical framework for studying the effects of frequency-dependent ecological interactions on the evolutionary dynamics of pre-existing resistance. First, we find that ecological interactions significantly expand the parameter regime under which we expect to observe pre-existing resistance. Next, even when positive ecological interactions between mutants and ancestors are rare, these resistant clones provide the primary mode of evolved resistance because even weak positive interaction leads to significantly longer extinction times. We then find that even in the case where mutation supply alone is sufficient to predict pre-existing resistance, frequency-dependent ecological forces still contribute a strong evolutionary pressure that selects for increasingly positive ecological effects (negative frequency-dependent selection). Finally, we genetically engineer several of the most common clinically observed resistance mechanisms to targeted therapies in NSCLC, a treatment notorious for pre-existing resistance. We find that each engineered mutant displays a positive ecological interaction with their ancestor. As a whole, these results suggest that frequency-dependent ecological effects can play a crucial role in shaping the evolutionary dynamics of pre-existing resistance.

Evaluating the genetic diversity of the Plasmodium vivax siap2 locus: A promising candidate for an effective malaria vaccine?

Malaria is the deadliest parasitic disease in the world. Traditional control measures have become less effective; hence, there is a need to explore alternative strategies, such as antimalarial vaccines. However, designing an anti-Plasmodium vivax vaccine is considered a challenge due to the complex parasite biology and the antigens' high genetic diversity. Recently, the sporozoite invasion-associated protein 2 (SIAP2) has been suggested as a potential antigen to be considered in vaccine design due to its significance during hepatocyte invasion. However, its use may be limited by the incomplete understanding of gene/protein diversity. Here, the genetic diversity of pvsiap2 using P. vivax DNA samples from Colombia was assessed. Through PCR amplification and sequencing, we compared the Colombian sequences with available worldwide sequences, revealing that pvsiap2 displays low genetic diversity. Molecular evolutionary analyses showed that pvsiap2 appears to be influenced by directional selection. Moreover, the haplotypes found differ by a few mutational steps and several of them were shared between different geographical areas. On the other hand, several conserved regions within PvSIAP2 were predicted as potential B-cell or T-cell epitopes. Considering these characteristics and its role in hepatocyte invasion, the PvSIAP2 protein emerges as a promising antigen to be considered in a multi-antigen-multi-stage (multivalent) fully effective vaccine against P. vivax malaria.

Antimalarial Drug Combination Predictions Using the Machine Learning Synergy Predictor (MLSyPred©) tool

PURPOSE

Antimalarial drug resistance is a global public health problem that leads to treatment failure. Synergistic drug combinations can improve treatment outcomes and delay the development of drug resistance. Here, we describe the implementation of a freely available computational tool, Machine Learning Synergy Predictor (MLSyPred©), to predict potential synergy in antimalarial drug combinations.

METHODS

The MLSyPred© synergy prediction method extracts molecular fingerprints from the drugs' biochemical structures to use as features and also cleans and prepares the raw data. Five machine learning algorithms (Logistic Regression, Random Forest, Support vector machine, Ada Boost, and Gradient Boost) were implemented to build prediction models. Implementation and application of the MLSyPred© tool were tested using datasets from 1540 combinations of 79 drugs and compounds biologically evaluated in pairs for three strains of Plasmodium falciparum (3D7, HB3, and Dd2).

RESULTS

The best prediction models were obtained using Logistic Regression for antimalarials with the strains Dd2 and HB3 (0.81 and 0.70 AUC, respectively) and Random Forest for antimalarials with 3D7 (0.69 AUC). The MLSyPred© tool yielded 45% precision for synergistically predicted antimalarial drug combinations that were annotated and biologically validated, thus confirming the functionality and applicability of the tool.

CONCLUSION

 The MLSyPred© tool is freely available and represents a promising strategy for discovering potential synergistic drug combinations for further development as novel antimalarial therapies.

Repurposing FDA-approved drugs to target malaria through inhibition of dihydrofolate reductase in the folate biosynthesis pathway: A prospective approach

Dihydrofolate reductase (DHFR) is a ubiquitous enzyme that regulates the biosynthesis of tetrahydrofolate among various species of Plasmodium parasite. It is a validated target of the antifolate drug pyrimethamine (Pyr) in Plasmodium falciparum (Pf), but its clinical efficacy has been hampered due to the emergence of drug resistance. This has made the attempt to screen Food & Drug Administration-approved drugs against wild- and mutant PfDHFR by employing an in-silico pipeline to identify potent candidates. The current study has followed a virtual screening approach for identifying potential DHFR inhibitors from DrugBank database, based on a structure similarity search of candidates, followed by absorption, distribution, metabolism, and excretion estimation. The screened drugs were subjected to various parameters like docking, molecular mechanics with generalized born and surface area solvation calculations, and molecular simulations. We have thus identified two potential drug candidates, duloxetine and guanethidine, which can be repurposed to be tested for their efficacy against wild type and drug resistant falciparum malaria.

Putative molecular markers of Plasmodium falciparum resistance to antimalarial drugs in malaria parasites from Ghana

Introduction

Antimalarial drugs including artemisinin-based combination therapy (ACT) regimens and sulphadoxine-pyrimethamine (SP) are used in Ghana for malaria therapeutics and prophylaxis respectively. The genetic basis of Plasmodium falciparum development of drug resistance involves single nucleotide polymorphisms in genes encoding proteins for multiple cellular and metabolic processes. The prevalence of single nucleotide polymorphisms in nine P. falciparum genes linked to ACT and SP resistance in the malaria parasite population was determined.

Methods

Archived filter paper blood blot samples from patients aged 9 years and below with uncomplicated malaria reporting at 10 sentinel sites located in three ecological zones for the Malaria Therapeutic Efficacy Studies were used. The samples used were collected from 2007-2018 malaria transmission seasons and mutations in the genes were detected using PCR and Sanger sequencing.

Results

In all 1,142 samples were used for the study. For falcipain-2 gene (pffp2), Sanger sequencing was successful for 872 samples and were further analysed. The prevalence of the mutants was 45% (392/872) with pffp2 markers V51I and S59F occurring in 15.0% (128/872) and 3.0% (26/872) of the samples respectively. Prevalence of other P. falciparum gene mutations: coronin (pfcoronin) was 44.8% (37/90); cysteine desulfurase (pfnfs) was 73.9% (68/92); apicoplast ribosomal protein S10 (pfarps10) was 36.8% (35/95); ferredoxin (pffd) was 8.8% (8/91); multidrug resistance protein-1 (pfmrp1) was 95.2.0% (80/84); multidrug resistance protein-2 (pfmrp2) was 91.4% (32/35); dihydrofolate reductase (pfdhfr) was 99.0% (84/85); dihydropteroate synthase (pfdhps) was 72% (68/95).

Discussion

The observation of numerous mutations in these genes of interest in the Ghanaian isolates, some of which have been implicated in delayed parasite clearance is of great interest. The presence of these genotypes may account for the decline in the efficacies of ACT regimens being used to treat uncomplicated malaria in the country. The need for continuous monitoring of these genetic markers to give first-hand information on parasite susceptibility to antimalarial drugs to inform policy makers and stakeholders in malaria elimination in the country is further discussed.

Long-Read Sequencing and De Novo Genome Assembly Pipeline of Two Plasmodium falciparum Clones (Pf3D7, PfW2) Using Only the PromethION Sequencer from Oxford Nanopore Technologies without Whole-Genome Amplification

Antimalarial drug resistance has become a real public health problem despite WHO measures. New sequencing technologies make it possible to investigate genomic variations associated with resistant phenotypes at the genome-wide scale. Based on the use of hemisynthetic nanopores, the PromethION technology from Oxford Nanopore Technologies can produce long-read sequences, in contrast to previous short-read technologies used as the gold standard to sequence Plasmodium. Two clones of P. falciparum (Pf3D7 and PfW2) were sequenced in long-read using the PromethION sequencer from Oxford Nanopore Technologies without genomic amplification. This made it possible to create a processing analysis pipeline for human Plasmodium with ONT Fastq only. De novo assembly revealed N50 lengths of 18,488 kb and 17,502 kb for the Pf3D7 and PfW2, respectively. The genome size was estimated at 23,235,407 base pairs for the Pf3D7 clone and 21,712,038 base pairs for the PfW2 clone. The average genome coverage depth was estimated at 787X and 653X for the Pf3D7 and PfW2 clones, respectively. This study proposes an assembly processing pipeline for the human Plasmodium genome using software adapted to large ONT data and the high AT percentage of Plasmodium. This search provides all the parameters which were optimized for use with the software selected in the pipeline.

The role of P450 enzymes in malaria and other vector-borne infectious diseases

Vector-borne infectious diseases are still an important global health problem. Malaria is the most important among them, mainly pediatric, life-threatening disease. Malaria and other vector-borne disorders caused by parasites, bacteria, and viruses have a strong impact on public health and significant economic costs. Most vector-borne diseases could be prevented by vector control, with attention to the ecological and biodiversity conservation aspects. Chemical control with pesticides and insecticides is widely used as a measure of prevention although increasing resistance to insecticides is a serious issue in vector control. Metabolic resistance is the most common mechanism and poses a big challenge. Insect enzyme systems, including monooxygenase CYP P450 enzymes, are employed by vectors mainly to metabolize insecticides thus causing resistance. The discovery and application of natural specific inhibitors/blockers of vector P450 enzymes as synergists for commonly used pesticides will contribute to the "greening" of insecticides. Besides vector CYPs, host CYP enzymes could also be exploited to fight against vector-borne diseases: using mostly their detoxifying properties and involvement in the immune response. Here, we review published research data on P450 enzymes from all players in vector-borne infections, that is, pathogens, vectors, and hosts, regarding the potential role of CYPs in disease. We discuss strategies on how to exploit cytochromes P450 in vector-borne disease control.

Direct long read visualization reveals metabolic interplay between two antimalarial drug targets

Increases in the copy number of large genomic regions, termed genome amplification, are an important adaptive strategy for malaria parasites. Numerous amplifications across the Plasmodium falciparum genome contribute directly to drug resistance or impact the fitness of this protozoan parasite. During the characterization of parasite lines with amplifications of the dihydroorotate dehydrogenase (DHODH) gene, we detected increased copies of an additional genomic region that encompassed 3 genes (~5 kb) including GTP cyclohydrolase I (GCH1 amplicon). While this gene is reported to increase the fitness of antifolate resistant parasites, GCH1 amplicons had not previously been implicated in any other antimalarial resistance context. Here, we further explored the association between GCH1 and DHODH copy number. Using long read sequencing and single read visualization, we directly observed a higher number of tandem GCH1 amplicons in parasites with increased DHODH copies (up to 9 amplicons) compared to parental parasites (3 amplicons). While all GCH1 amplicons shared a consistent structure, expansions arose in 2-unit steps (from 3 to 5 to 7, etc copies). Adaptive evolution of DHODH and GCH1 loci was further bolstered when we evaluated prior selection experiments; DHODH amplification was only successful in parasite lines with pre-existing GCH1 amplicons. These observations, combined with the direct connection between metabolic pathways that contain these enzymes, lead us to propose that the GCH1 locus is beneficial for the fitness of parasites exposed to DHODH inhibitors. This finding highlights the importance of studying variation within individual parasite genomes as well as biochemical connections of drug targets as novel antimalarials move towards clinical approval.

Prediction of malaria positivity using patients' demographic and environmental features and clinical symptoms to complement parasitological confirmation before treatment

BACKGROUND

Current malaria diagnosis methods that rely on microscopy and Histidine Rich Protein-2 (HRP2)-based rapid diagnostic tests (RDT) have drawbacks that necessitate the development of improved and complementary malaria diagnostic methods to overcome some or all these limitations. Consequently, the addition of automated detection and classification of malaria using laboratory methods can provide patients with more accurate and faster diagnosis. Therefore, this study used a machine-learning model to predict Plasmodium falciparum (Pf) antigen positivity (presence of malaria) based on sociodemographic behaviour, environment, and clinical features.

METHOD

Data from 200 Nigerian patients were used to develop predictive models using nested cross-validation and sequential backward feature selection (SBFS), with 80% of the dataset randomly selected for training and optimisation and the remaining 20% for testing the models. Outcomes were classified as Pf-positive or Pf-negative, corresponding to the presence or absence of malaria, respectively.

RESULTS

Among the three machine learning models examined, the penalised logistic regression model had the best area under the receiver operating characteristic curve for the training set (AUC = 84%; 95% confidence interval [CI]: 75-93%) and test set (AUC = 83%; 95% CI: 63-100%). Increased odds of malaria were associated with higher body weight (adjusted odds ratio (AOR) = 4.50, 95% CI: 2.27 to 8.01, p < 0.0001). Even though the association between the odds of having malaria and body temperature was not significant, patients with high body temperature had higher odds of testing positive for the Pf antigen than those who did not have high body temperature (AOR = 1.40, 95% CI: 0.99 to 1.91, p = 0.068). In addition, patients who had bushes in their surroundings (AOR = 2.60, 95% CI: 1.30 to 4.66, p = 0.006) or experienced fever (AOR = 2.10, 95% CI: 0.88 to 4.24, p = 0.099), headache (AOR = 2.07; 95% CI: 0.95 to 3.95, p = 0.068), muscle pain (AOR = 1.49; 95% CI: 0.66 to 3.39, p = 0.333), and vomiting (AOR = 2.32; 95% CI: 0.85 to 6.82, p = 0.097) were more likely to experience malaria. In contrast, decreased odds of malaria were associated with age (AOR = 0.62, 95% CI: 0.41 to 0.90, p = 0.012) and BMI (AOR = 0.47, 95% CI: 0.26 to 0.80, p = 0.006).

CONCLUSION

Newly developed routinely collected baseline sociodemographic, environmental, and clinical features to predict Pf antigen positivity may be a valuable tool for clinical decision-making.

Naphthyl bearing 1,3,4-thiadiazoleacetamides targeting the parasitic folate pathway as anti-infectious agents: in silico, synthesis, and biological approach

Malaria is still a complex and lethal parasitic infectious disease, despite the availability of effective antimalarial drugs. Resistance of malaria parasites to current treatments necessitates new antimalarials targeting P. falciparum proteins. The present study reported the design and synthesis of a series of a 2-(4-substituted piperazin-1-yl)-N-(5-((naphthalen-2-yloxy)methyl)-1,3,4-thiadiazol-2-yl)acetamide hybrids for the inhibition of Plasmodium falciparum dihydrofolate reductase (PfDHFR) using computational biology tools followed by chemical synthesis, structural characterization, and functional analysis. The synthesized compounds were evaluated for their in vitro antimalarial activity against CQ-sensitive PfNF54 and CQ-resistant PfW2 strain. Compounds T5 and T6 are the most active compounds having anti-plasmodial activity against PfNF54 with IC50 values of 0.94 and 3.46 μM respectively. Compound T8 is the most active against the PfW2 strain having an IC50 of 3.91 μM. Further, these active hybrids (T5, T6, and T8) were also evaluated for enzyme inhibition assay against PfDHFR. All the tested compounds were non-toxic against the Hek293 cell line with good selectivity indices. Hemolysis assay also showed non-toxicity of these compounds on normal uninfected human RBCs. In silico molecular docking studies were carried out in the binding pocket of both the wild-type and quadruple mutant Pf-DHFR-TS to gain further insights into probable modes of action of active compounds. ADME prediction and physiochemical properties support their drug-likeness. Additionally, they were screened for antileishmanial activity against L. donovani promastigotes to explore broader applications. Thus, this study provides molecular frameworks for developing potent antimalarials and antileishmanial agents.

Marmesin isolated from Celtis durandii Engl. root bioactive fraction inhibits β-hematin formation and contributes to antiplasmodial activity

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria is a leading cause of death in many developing countries, especially in sub-Saharan Africa. Nigeria is endowed with an abundance of medicinal plants, many of which are used to treat malaria. Celtis durandii Engl. is one such plant used as a traditional antimalarial remedy in southeast Nigeria. However, its antiplasmodial potential is poorly explored.

AIM OF THE STUDY

The study aimed at identifying the antiplasmodial components of C. durandii root extract through antiplasmodial activity-guided fractionation.

MATERIALS AND METHODS

Dichloromethane/methanol mixture extract (1:1 v/v) of C. durandii root was prepared and partitioned against water to obtain the organic phase, which was further separated by column chromatography into nine (C1 - C9) fractions. The antiplasmodial activity was evaluated by in vitro screening of the different fractions against drug-sensitive and drug-resistant Plasmodium falciparum strains. Further purification of the active column fractions resulted in a potent anti-Plasmodial compound that was subsequently investigated for its effect on β-hematin formation. Additionally, the isolated compound was characterized and identified as marmesin using mass spectrometry and nuclear magnetic resonance spectroscopy.

RESULTS

Celtis durandii root extract exhibited promising antiplasmodial activity {IC50 (μg/ml) 5.92, 6.04, and 6.92} against PfW2mef, PfINDO, and Pf3D7 respectively. Pooled fractions with good antiplasmodial activity {IC50 (μg/ml) Pf3D7: 3.99; PfINDO: 2.24} and selectivity for the parasites (SI: 21) yielded a compound that was fourteen-fold potent in antiplasmodial activity against Pf3D7(IC50: 0.28 μg/ml). It also inhibited β-hematin formation with an IC50 = 150 μM. Further studies using spectral data, literature, and chemical databases identified the purified compound as marmesin.

CONCLUSION

This work has demonstrated that Celtis durandii root extract has good antiplasmodial activity against drug-sensitive and drug-resistant P. falciparum. The inhibition of β-hematin formation by marmesin accounts in part for this activity.

Antibiotic persistence and its impact on the environment

From boon molecules to molecules contributing to rising concern has been the sojourn of antibiotics. The problem of antibiotic contamination has gotten worse due to antibiotics' pervasive use in every aspect of the environment. One such consequence of pollution is the increase in infections with antibiotic resistance. All known antimicrobials being used for human benefit lead to their repetitive and routine release into the environment. The misuse of antibiotics has aggravated the situation to a level that we are short of antibiotics to treat infections as organisms have developed resistance against them. Overconsumption is not just limited to human health care, but also occurs in other areas such as aquaculture, livestock, and veterinary applications for the purpose of improving feed and meat products. Due to their harmful effects on non-target species, the trace level of antibiotics in the aquatic ecosystem presents a significant problem. Since the introduction of antibiotics into the environment is more than their removal, they have been given the status of persistent pollutants. The buildup of antibiotics in the environment threatens aquatic life and may lead to bacterial strains developing resistance. As newer organisms are becoming resistant, there exists a shortage of antibiotics to treat infections. This has presented a very critical problem for the health-care community. Another rising concern is that the development of newer drug molecules as antibiotics is minimal. This review article critically explains the cause and nature of the pollution and the effects of this emerging trend. Also, in the latter sections, why we need newer antibiotics is questioned and discussed.

Antimalarial Activity of Anacardium occidentale Leaf Extracts Against Plasmodium falciparum Transketolase (PfTK)

BACKGROUND

As per estimates by WHO in 2021 almost half of the world's population was at risk of malaria and > 0.6 million deaths were attributed to malaria. Therefore, the present study was aimed to explore the antimalarial activity of extracts derived from the leaves of the plant Anacardium occidentale L., which has been used traditionally for the treatment of malaria. Different extracts of A. occidentale leaves were prepared and tested for their inhibitory activity against recombinant P. falciparum transketolase (rPfTK) enzyme, in vitro. Further, growth inhibitory activity against cultivated blood stage P. falciparum parasites (3D7 strain), was studied using SYBR Green fluorescence-based in vitro assays. Acute toxicity of the hydro alcoholic extracts of leaves of A. occidentale (HELA) at different concentrations was evaluated on mice and Zebra fish embryos. HELA showed 75.45 ± 0.35% inhibitory activity against the recombinant PfTk and 99.31 ± 0.08% growth inhibition against intra-erythrocytic stages of P. falciparum at the maximum concentration (50 µg/ml) with IC50 of 4.17 ± 0.22 µg/ml. The toxicity test results showed that the heartbeat, somite formation, tail detachment and hatching of embryos were not affected when Zebra fish embryos were treated with 0.1 to 10 µg/ml of the extract. However, at higher concentrations of the extract, at 48 h (1000 µg/ml) and 96 h (100 µg/ml and 1000 µg/ml, respectively) there was no heartbeat in the fish embryos. In the acute oral toxicity tests performed on mice, the extract showed no toxicity up to 300 mg/kg body weight in mice.

CONCLUSION

The hydro-alcoholic extract of leaves of A. occidentale L. showed potent antimalarial activity against blood stage P. falciparum. Based on the observed inhibitory activity on the transketolase enzyme of P. falciparum it is likely that this enzyme is the target for the development of bioactive molecules present in the plant extracts. The promising anti-malarial activity of purified compounds from leaves of A. occidentale needs to be further explored for development of new anti-malarial therapy.

Therapeutic Potential of Marine-Derived Cyclic Peptides as Antiparasitic Agents

Parasitic diseases still compromise human health. Some of the currently available therapeutic drugs have limitations considering their adverse effects, questionable efficacy, and long treatment, which have encouraged drug resistance. There is an urgent need to find new, safe, effective, and affordable antiparasitic drugs. Marine-derived cyclic peptides have been increasingly screened as candidates for developing new drugs. Therefore, in this review, a systematic analysis of the scientific literature was performed and 25 marine-derived cyclic peptides with antiparasitic activity (1-25) were found. Antimalarial activity is the most reported (51%), followed by antileishmanial (27%) and antitrypanosomal (20%) activities. Some compounds showed promising antiparasitic activity at the nM scale, being active against various parasites. The mechanisms of action and targets for some of the compounds have been investigated, revealing different strategies against parasites.

Genetic polymorphism and natural selection of the erythrocyte binding antigen 175 region II in Plasmodium falciparum populations from Myanmar and Vietnam

Plasmodium falciparum erythrocyte binding antigen 175 (PfEBA-175) plays essential role in erythrocyte invasion by the parasite and is a leading vaccine candidate. However, its genetic diversity in global isolates is a concern in developing an universal vaccine incorporating this protein. This study aimed to investigate genetic polymorphisms and natural selection of pfeba-175 region II (RII) in Myanmar and Vietnam P. falciparum isolates. Vietnam pfeba-175 RII displayed a low genetic polymorphism, while Myanmar pfeba-175 RII showed high levels of genetic diversity across the region. Point mutations, deletion, and recombinations were main factors contributing to genetic diversities in P. falciparum populations. Global pfeba-175 RII revealed similar, but not identical, genetic polymorphisms and natural selection profiles. Despite profiles of amino acid substitutions differed among populations, five major amino acid changes (K279E, E403K, K481I, Q584K, and R664) were commonly detected in global pfeba-175 RII populations. Haplotype network and genetic differentiation analyses of global pfeba-175 RII populations demonstrated no geographical relationships. Non-neglectable level of genetic diversity was observed in global pfeba-175 RII populations, emphasizing the need to consider this when designing an effective vaccine based on this protein. This study underscores the importance of the continuous monitoring of genetic diversity of pfeba-175 RII in the global P. falciparum populations.

The landscape of drug resistance in Plasmodium falciparum malaria in the Democratic Republic of Congo: a mapping systematic review

CONTEXT

The Democratic Republic of Congo (DRC), one of the most malaria-affected countries worldwide, is a potential hub for global drug-resistant malaria. This study aimed at summarizing and mapping surveys of malaria parasites carrying molecular markers of drug-resistance across the country.

METHODS

A systematic mapping review was carried out before July 2023 by searching for relevant articles through seven databases (PubMed, Embase, Scopus, African Journal Online, African Index Medicus, Bioline and Web of Science).

RESULTS

We identified 1541 primary studies of which 29 fulfilled inclusion criteria and provided information related to 6385 Plasmodium falciparum clinical isolates (collected from 2000 to 2020). We noted the PfCRT K76T mutation encoding for chloroquine-resistance in median 32.1% [interquartile interval, IQR: 45.2] of analyzed malaria parasites. The proportion of parasites carrying this mutation decreased overtime, but wide geographic variations persisted. A single isolate had encoded the PfK13 R561H substitution that is invoked in artemisinin-resistance emergence in the Great Lakes region of Africa. Parasites carrying various mutations linked to resistance to the sulfadoxine-pyrimethamine combination were widespread and reflected a moderate resistance profile (PfDHPS A437G: 99.5% [IQR: 3.9]; PfDHPS K540E: 38.9% [IQR: 47.7]) with median 13.1% [IQR: 10.3] of them being quintuple IRN-GE mutants (i.e., parasites carrying the PfDHFR N51I-C59R-S108N and PfDHPS A437G-K540E mutations). These quintuple mutants tended to prevail in eastern regions of the country. Among circulating parasites, we did not record any parasites harboring mutations related to mefloquine-resistance, but we could suspect those with decreased susceptibility to quinine, amodiaquine, and lumefantrine based on corresponding molecular surrogates.

CONCLUSIONS

Drug resistance poses a serious threat to existing malaria therapies and chemoprevention options in the DRC. This review provides a baseline for monitoring public health efforts as well as evidence for decision-making in support of national malaria policies and for implementing regionally tailored control measures across the country.

Changes in contributions of different Anopheles vector species to malaria transmission in east and southern Africa from 2000 to 2022

BACKGROUND

Malaria transmission in Africa is facilitated by multiple species of Anopheles mosquitoes. These vectors have different behaviors and vectorial capacities and are affected differently by vector control interventions, such as insecticide-treated nets and indoor residual spraying. This review aimed to assess changes in the contribution of different vector species to malaria transmission in east and southern Africa over 20 years of widespread insecticide-based vector control.

METHODS

We searched PubMed, Global Health, and Web of Science online databases for articles published between January 2000 and April 2023 that provided species-specific sporozoite rates for different malaria vectors in east and southern Africa. We extracted data on study characteristics, biting rates, sporozoite infection proportions, and entomological inoculation rates (EIR). Using EIR data, the proportional contribution of each species to malaria transmission was estimated.

RESULTS

Studies conducted between 2000 and 2010 identified the Anopheles gambiae complex as the primary malaria vector, while studies conducted from 2011 to 2021 indicated the dominance of Anopheles funestus. From 2000 to 2010, in 57% of sites, An. gambiae demonstrated higher parasite infection prevalence than other Anopheles species. Anopheles gambiae also accounted for over 50% of EIR in 76% of the study sites. Conversely, from 2011 to 2021, An. funestus dominated with higher infection rates than other Anopheles in 58% of sites and a majority EIR contribution in 63% of sites. This trend coincided with a decline in overall EIR and the proportion of sporozoite-infected An. gambiae. The main vectors in the An. gambiae complex in the region were Anopheles arabiensis and An. gambiae sensu stricto (s.s.), while the important member of the An. funestus group was An. funestus s.s.

CONCLUSION

The contribution of different vector species in malaria transmission has changed over the past 20 years. As the role of An. gambiae has declined, An. funestus now appears to be dominant in most settings in east and southern Africa. Other secondary vector species may play minor roles in specific localities. To improve malaria control in the region, vector control should be optimized to match these entomological trends, considering the different ecologies and behaviors of the dominant vector species.

Acute and subacute oral toxicity of artemisinin-hydroxychloroquine sulfate tablets in beagle dogs

Artemisinin-hydroxychloroquine sulfate tablets (AH) are regarded as a relatively inexpensive and novel combination therapy for the treatment of various forms of malaria, particularly aminoquinoline drugs-resistant strains of Plasmodium falciparum. Our aim was to conduct acute and subacute oral toxicity studies in non-rodents to obtain more nonclinical data on the safety of AH. Acute toxicity evaluation was performed in beagle dogs at single doses of 230, 530, 790, 1180, 2660, and 5000 mg/kg. Beagle dogs at doses of 0, 56, 84, and 126 mg/kg were used to assess subacute toxicity for 14 days. The approximate lethal dose range for acute oral administration of AH in dogs is found to be 790-1180 mg/kg, and toxic symptoms prior to death include gait instability, limb weakness, mental fatigue, tachypnea, and convulsion. Repeated doses of AH in dogs caused vomiting, soft feces, decreased activity, anorexia, and splenic red pulp vacuolation. Of note, AH could reduce body weight gain and prolong the QTc interval of individual dogs. Therefore, the no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) of oral administration of AH for 14 days in dogs are determined to be 84 mg/kg and 126 mg/kg, respectively.

Impact of the microbiome on mosquito-borne diseases

Mosquito-borne diseases present a significant threat to human health, with the possibility of outbreaks of new mosquito-borne diseases always looming. Unfortunately, current measures to combat these diseases such as vaccines and drugs are often either unavailable or ineffective. However, recent studies on microbiomes may reveal promising strategies to fight these diseases. In this review, we examine recent advances in our understanding of the effects of both the mosquito and vertebrate microbiomes on mosquito-borne diseases. We argue that the mosquito microbiome can have direct and indirect impacts on the transmission of these diseases, with mosquito symbiotic microorganisms, particularly Wolbachia bacteria, showing potential for controlling mosquito-borne diseases. Moreover, the skin microbiome of vertebrates plays a significant role in mosquito preferences, while the gut microbiome has an impact on the progression of mosquito-borne diseases in humans. As researchers continue to explore the role of microbiomes in mosquito-borne diseases, we highlight some promising future directions for this field. Ultimately, a better understanding of the interplay between mosquitoes, their hosts, pathogens, and the microbiomes of mosquitoes and hosts may hold the key to preventing and controlling mosquito-borne diseases.

Prioritised identification of structural classes of natural products from higher plants in the expedition of antimalarial drug discovery

The emergence and spread of drug-recalcitrant Plasmodium falciparum parasites threaten to reverse the gains made in the fight against malaria. Urgent measures need to be taken to curb this impending challenge. The higher plant-derived sesquiterpene, quinoline alkaloids, and naphthoquinone natural product classes of compounds have previously served as phenomenal chemical scaffolds from which integral antimalarial drugs were developed. Historical successes serve as an inspiration for the continued investigation of plant-derived natural products compounds in search of novel molecular templates from which new antimalarial drugs could be developed. The aim of this study was to identify potential chemical scaffolds for malaria drug discovery following analysis of historical data on phytochemicals screened in vitro against P. falciparum. To identify these novel scaffolds, we queried an in-house manually curated database of plant-derived natural product compounds and their in vitro biological data. Natural products were assigned to different structural classes using NPClassifier. To identify the most promising chemical scaffolds, we then correlated natural compound class with bioactivity and other data, namely (i) potency, (ii) resistance index, (iii) selectivity index and (iv) physicochemical properties. We used an unbiased scoring system to rank the different natural product classes based on the assessment of their bioactivity data. From this analysis we identified the top-ranked natural product pathway as the alkaloids. The top three ranked super classes identified were (i) pseudoalkaloids, (ii) naphthalenes and (iii) tyrosine alkaloids and the top five ranked classes (i) quassinoids (of super class triterpenoids), (ii) steroidal alkaloids (of super class pseudoalkaloids) (iii) cycloeudesmane sesquiterpenoids (of super class triterpenoids) (iv) isoquinoline alkaloids (of super class tyrosine alkaloids) and (v) naphthoquinones (of super class naphthalenes). Launched chemical space of these identified classes of compounds was, by and large, distinct from that of 'legacy' antimalarial drugs. Our study was able to identify chemical scaffolds with acceptable biological properties that are structurally different from current and previously used antimalarial drugs. These molecules have the potential to be developed into new antimalarial drugs.

Antimalarial drug efficacy and resistance in malaria-endemic countries in HANMAT-PIAM_net countries of the Eastern Mediterranean Region 2016-2020: Clinical and genetic studies

INTRODUCTION

The World Health Organization recommends regular monitoring of the efficacy of nationally recommended antimalarial drugs. We present the results of studies on the efficacy of recommended antimalarials and molecular markers of artemisinin and partner resistance in Afghanistan, Pakistan, Somalia, Sudan and Yemen.

METHODS

Single-arm prospective studies were conducted to evaluate the efficacy of artesunate-sulfadoxine-pyrimethamine (ASSP) in Afghanistan and Pakistan, artemether-lumefantrine (AL) in all countries, or dihydroartemisinin-piperaquine (DP) in Sudan for the treatment of Plasmodium falciparum. The efficacy of chloroquine (CQ) and AL for the treatment of Plasmodium vivax was evaluated in Afghanistan and Somalia, respectively. Patients were treated and monitored for 28 (CQ, ASSP and AL) or 42 (DP) days. Polymerase chain reaction (PCR)-corrected cure rate and parasite positivity rate at Day 3 were estimated. Mutations in the P. falciparum kelch 13 (Pfk13) gene and amplifications of plasmepsin (Pfpm2) and multidrug resistance-1 (Pfmdr-1) genes were also studied.

RESULTS

A total of 1680 (249 for ASSP, 1079 for AL and 352 for DP) falciparum cases were successfully assessed. A PCR-adjusted ASSP cure rate of 100% was observed in Afghanistan and Pakistan. For AL, the cure rate was 100% in all but four sites in Sudan, where cure rates ranged from 92.1% to 98.8%. All but one patient were parasite-free at Day 3. For P. vivax, cure rates were 98.2% for CQ and 100% for AL. None of the samples from Afghanistan, Pakistan and Yemen had a Pfk13 mutation known to be associated with artemisinin resistance. In Sudan, the validated Pfk13 R622I mutation accounted for 53.8% (14/26) of the detected non-synonymous Pfk13 mutations, most of which were repeatedly detected in Gadaref. A prevalence of 2.7% and 9.3% of Pfmdr1 amplification was observed in Pakistan and Yemen, respectively.

CONCLUSION

High efficacy of ASSP, AL and DP in the treatment of uncomplicated falciparum infection and of CQ and AL in the treatment of P. vivax was observed in the respective countries. The repeated detection of a relatively high rate of Pfk13 R622I mutation in Sudan underscores the need for close monitoring of the efficacy of recommended ACTs, parasite clearance rates and Pfk13 mutations in Sudan and beyond. Registration numbers of the trials: ACTRN12622000944730 and ACTRN12622000873729 for Afghanistan, ACTRN12620000426987 and ACTRN12617001025325 for Pakistan, ACTRN12618001224213 for Somalia, ACTRN12617000276358, ACTRN12622000930785 and ACTRN12618001800213 for Sudan and ACTRN12617000283370 for Yemen.

Increasing Prevalence of Artemisinin-Resistant HRP2-Negative Malaria in Eritrea

BACKGROUND

Although the clinical efficacy of antimalarial artemisinin-based combination therapies in Africa remains high, the recent emergence of partial resistance to artemisinin in Plasmodium falciparum on the continent is troubling, given the lack of alternative treatments.

METHODS

In this study, we used data from drug-efficacy studies conducted between 2016 and 2019 that evaluated 3-day courses of artemisinin-based combination therapy (artesunate-amodiaquine or artemether-lumefantrine) for uncomplicated malaria in Eritrea to estimate the percentage of patients with day-3 positivity (i.e., persistent P. falciparum parasitemia 3 days after the initiation of therapy). We also assayed parasites for mutations in Pfkelch13 as predictive markers of partial resistance to artemisinin and screened for deletions in hrp2 and hrp3 that result in variable performance of histidine rich protein 2 (HRP2)-based rapid diagnostic tests for malaria.

RESULTS

We noted an increase in the percentage of patients with day-3 positivity from 0.4% (1 of 273) in 2016 to 1.9% (4 of 209) in 2017 and 4.2% (15 of 359) in 2019. An increase was also noted in the prevalence of the Pfkelch13 R622I mutation, which was detected in 109 of 818 isolates before treatment, from 8.6% (24 of 278) in 2016 to 21.0% (69 of 329) in 2019. The odds of day-3 positivity increased by a factor of 6.2 (95% confidence interval, 2.5 to 15.5) among the patients with Pfkelch13 622I variant parasites. Partial resistance to artemisinin, as defined by the World Health Organization, was observed in Eritrea. More than 5% of the patients younger than 15 years of age with day-3 positivity also had parasites that carried Pfkelch13 R622I. In vitro, the R622I mutation conferred a low level of resistance to artemisinin when edited into NF54 and Dd2 parasite lines. Deletions in both hrp2 and hrp3 were identified in 16.9% of the parasites that carried the Pfkelch13 R622I mutation, which made them potentially undetectable by HRP2-based rapid diagnostic tests.

CONCLUSIONS

The emergence and spread of P. falciparum lineages with both Pfkelch13-mediated partial resistance to artemisinin and deletions in hrp2 and hrp3 in Eritrea threaten to compromise regional malaria control and elimination campaigns. (Funded by the Bill and Melinda Gates Foundation and others; Australian New Zealand Clinical Trials Registry numbers, ACTRN12618001223224, ACTRN12618000353291, and ACTRN12619000859189.).

Strategies for deploying triple artemisinin-based combination therapy in the Greater Mekong Subregion

BACKGROUND

This is a qualitative study to identify implementation challenges for deploying triple artemisinin-based combination therapy (TACT) in the Greater Mekong Subregion (GMS) of Southeast Asia and to explore strategies to overcome these challenges.

METHODS

In-depth interviews were conducted in three countries that have repeatedly been confronted with ACT failures: Cambodia, Vietnam, and Lao PDR. Thirty-nine key stakeholders in the healthcare systems in these countries were interviewed. One participatory workshop was conducted in Cambodia, where scenarios for potential TACT deployment were discussed.

RESULTS

The results section is organized around four strategic themes that emerged from the data: policy support, data and evidence, logistics and operation, and downstream engagement. The study revealed that countries in the GMS currently rely on ACT to eliminate Plasmodium falciparum malaria by 2025. TACT is, however, considered to be a useful backup strategy in case of future treatment failures and to prevent the re-establishment of malaria. The study showed that a major challenge ahead is to engage decision makers and healthcare providers into deploying TACT, given the low case incidence of falciparum malaria in the GMS. Interview respondents were also skeptical whether healthcare providers would be willing to engage in new therapies for a disease they hardly encounter anymore. Hence, elaborate information dissemination strategies were considered appropriate and these strategies should especially target village malaria workers. Respondents proposed several regulatory and programmatic strategies to anticipate the formation of TACT markets in the GMS. These strategies include early dossier submission to streamline regulatory procedures, early stakeholder engagement strategies to shorten implementation timelines, and inclusion of TACT as second-line therapy to accelerate their introduction in case they are urgently needed.

CONCLUSIONS

This paper presents a qualitative study to identify implementation challenges for deploying TACT in the GMS and to explore strategies to overcome these challenges. The findings could benefit researchers and decision makers in strategizing towards potential future deployment of TACT in the GMS to combat artemisinin and partner drug resistance.

Therapeutic efficacy of artesunate-amodiaquine and artemether-lumefantrine for the treatment of uncomplicated falciparum malaria in Chad: clinical and genetic surveillance

BACKGROUND

Artesunate-amodiaquine (AS-AQ) and artemether-lumefantrine (AL) are the currently recommended first-and second-line therapies for uncomplicated Plasmodium falciparum infections in Chad. This study assessed the efficacy of these artemisinin-based combinations, proportion of day 3 positive patients, proportions of molecular markers associated with P. falciparum resistance to anti-malarial drugs and variable performance of HRP2-based malaria rapid diagnostic tests (RDTs).

METHODS

A single-arm prospective study assessing the efficacy of AS-AQ and AL at three sites (Doba, Kelo and Koyom) was conducted between November 2020 to January 2021. Febrile children aged 6 to 59 months with confirmed uncomplicated P. falciparum infection were enrolled sequentially first to AS-AQ and then AL at each site and followed up for 28 days. The primary endpoint was PCR-adjusted adequate clinical and parasitological response (ACPR). Samples collected on day 0 were analysed for mutations in pfkelch13, pfcrt, pfmdr-1, pfdhfr, pfdhps genes and deletions in pfhrp2/pfhrp3 genes.

RESULTS

By the end of 28-day follow-up, per-protocol PCR corrected ACPR of 97.8% (CI 95% 88.2-100) in Kelo and 100% in Doba and Kayoma were observed among AL treated patients. For ASAQ, 100% ACPR was found in all sites. All, but one patient, did not have parasites detected on day 3. Out of the 215 day 0 samples, 96.7% showed pfkelch13 wild type allele. Seven isolates carried nonsynonymous mutations not known to be associated artemisinin partial resistance (ART-R). Most of samples had a pfcrt wild type allele (79% to 89%). The most prevalent pfmdr-1 allele detected was the single mutant 184F (51.2%). For pfdhfr and pfdhps mutations, the quintuple mutant allele N51I/C59R/S108N + G437A/540E responsible for SP treatment failures in adults and children was not detected. Single deletion in the pfhrp2 and pfhrp3 gene were detected in 10/215 (4.7%) and 2/215 (0.9%), respectively. Dual pfhrp2/pfhrp3 deletions, potentially threatening the efficacy of HRP2-based RDTs, were observed in 5/215 (2.3%) isolates.

CONCLUSION

The results of this study confirm that AS-AQ and AL treatments are highly efficacious in study areas in Chad. The absence of known pfkelch13 mutations in the study sites and the high parasite clearance rate at day 3 suggest the absence of ART-R. The absence of pfdhfr/pfdhps quintuple or sextuple (quintuple + 581G) mutant supports the continued use of SP for IPTp during pregnancy. The presence of parasites with dual pfhrp2/pfhrp3 deletions, potentially threatening the efficacy of HRP2-based RDTs, warrants the continued surveillance. Trial registration ACTRN12622001476729.

Nationwide spatiotemporal drug resistance genetic profiling from over three decades in Indian Plasmodium falciparum and Plasmodium vivax isolates

BACKGROUND

Drug resistance is a serious impediment to efficient control and elimination of malaria in endemic areas.

METHODS

This study aimed at analysing the genetic profile of molecular drug resistance in Plasmodium falciparum and Plasmodium vivax parasites from India over a ~ 30-year period (1993-2019). Blood samples of P. falciparum and/or P. vivax-infected patients were collected from 14 regions across India. Plasmodial genome was extracted and used for PCR amplification and sequencing of drug resistance genes in P. falciparum (crt, dhps, dhfr, mdr1, k13) and P. vivax (crt-o, dhps, dhfr, mdr1, k12) field isolates.

RESULTS

The double mutant pfcrt SVMNT was highly predominant across the country over three decades, with restricted presence of triple mutant CVIET from Maharashtra in 2012. High rates of pfdhfr-pfdhps quadruple mutants were observed with marginal presence of "fully resistant" quintuple mutant ACIRNI-ISGEAA. Also, resistant pfdhfr and pfdhps haplotype has significantly increased in Delhi between 1994 and 2010. For pfmdr1, only 86Y and 184F mutations were present while no pfk13 mutations associated with artemisinin resistance were observed. Regarding P. vivax isolates, the pvcrt-o K10 "AAG" insertion was absent in all samples collected from Delhi in 2017. Pvdhps double mutant SGNAV was found only in Goa samples of year 2008 for the first time. The pvmdr1 908L, 958M and 1076L mutations were highly prevalent in Delhi and Haryana between 2015 and 2019 at complete fixation. One nonsynonymous novel pvk12 polymorphism was identified (K264R) in Goa.

CONCLUSIONS

These findings support continuous surveillance and characterization of P. falciparum and P. vivax populations as proxy for effectiveness of anti-malarial drugs in India, especially for independent emergence of artemisinin drug resistance as recently seen in Africa.

Plasmodium falciparum FIKK 9.1 kinase modeling to screen and identify potent antimalarial agents from chemical library

The Plasmodium FIKK kinases are diverged from human kinases structurally. They harbour conserved ATP-binding domains that are non-homologous to other existing kinases. FIKK9.1 kinase is considered as an essential protein for parasite survival. It is localized in major organelles present in parasite and trafficked throughout the infected RBC. It is speculated that FIKK9.1 may phosphorylate several substrates in the parasite's proteome and contribute to parasite survival. Therefore, FIKK9.1 is an attractive target that may lead to a novel class of antimalarials. To identify specific FIKK9.1 kinase inhibitors, we virtually screened organic structural scaffolds from a library of 623 entries. The top hits were identified based on conformations and molecular interactions with the ATP biophore. The hits were also validated under in vitro conditions. In this study, we identified seven top hit organic compounds that may arrest the growth of parasites by inhibiting FIKK9.1 kinase. Evaluation of top hit compounds in antimalarial activity assay identifies that the highly substituted 1,3-selenazolidin-2-imine 1 and thiophene 2 are inhibiting parasite growth with an IC50 of 3.2 ± 0.27 μg/ml and 3.13 ± 0.16 μg/ml, respectively. These functionalized heterocyclic compounds 1 and 2 kills the malaria parasite with an IC50 of 2.68 ± 0.02 μg/ml and 3.08 ± 0.14 μg/ml, respectively. Isothermal titration calorimetry analysis indicate that ATP is binding to the FIKK9.1 kinase. The dissociation constant (Kd) is measured to be 27.8 ± 2.07 μM with a stoichiometry of n = 1. The heterocyclic scaffolds 1 and 2 were abolishing the binding of ATP into the binding pocket. They in-turn reduce the ability of FIKK9.1 kinase to phosphorylate its substrate. Our study found that compounds 1 and 2 are potent inhibitor of FIKK9.1 kinase and the inhibition of FIKK9.1 kinase using small molecules disturbs the parasite life cycle and leads to the death of parasites. This provides new insight in development of novel antimalarials.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03677-x.

Ex vivo and In vitro antiplasmodial activities of approved drugs predicted to have antimalarial activities using chemogenomics and drug repositioning approach

High malaria mortality coupled with increased emergence of resistant multi-drug resistant strains of Plasmodium parasite, warrants the development of new and effective antimalarial drugs. However, drug design and discovery are costly and time-consuming with many active antimalarial compounds failing to get approved due to safety reasons. To address these challenges, the current study aimed at testing the antiplasmodial activities of approved drugs that were predicted using a target-similarity approach. This approach is based on the fact that if an approved drug used to treat another disease targets a protein similar to Plasmodium falciparum protein, then the drug will have a comparable effect on P. falciparum. In a previous study, in vitro antiplasmodial activities of 10 approved drugs was reported of the total 28 approved drugs. In this study, six out of 18 drugs that were previously not tested, namely epirubicin, irinotecan, venlafaxine, palbociclib, pelitinib, and PD153035 were tested for antiplasmodial activity. The drug susceptibility in vitro assays against five P. falciparum reference strains (D6, 3D7, W2, DD2, and F32 ART) and ex vivo assays against fresh clinical isolates were done using the malaria SYBR Green I assay. Standard antimalarial drugs were included as controls. Epirubicin and irinotecan showed excellent antiplasmodial ex vivo activity against field isolates with mean IC50 values of 0.044 ± 0.033 μM and 0.085 ± 0.055 μM, respectively. Similar activity was observed against W2 strain where epirubicin had an IC50 value of 0.004 ± 0.0009 μM, palbociclib 0.056 ± 0.006 μM, and pelinitib 0.057 ± 0.013 μM. For the DD2 strain, epirubicin, irinotecan and PD 153035 displayed potent antiplasmodial activity (IC50 < 1 μM). Epirubicin and irinotecan showed potent antiplasmodial activities (IC50 < 1 μM) against DD2, D6, 3D7, and F32 ART strains and field isolates. This shows the potential use of these drugs as antimalarials. All the tested drugs showed antiplasmodial activities with IC50 values below 20 μM, which suggests that our target similarity-based strategy is successful at predicting antiplasmodial activity of compounds thereby circumventing challenges in antimalarial drug discovery.