Malaria in 2022: Increasing challenges, cautious optimism

A promising class of antiprotozoal agents, design and synthesis of novel Pyrimidine-Cinnamoyl hybrids

Malaria, caused by parasitic protozoans of the Plasmodium genus, continues to be one of the greatest global health crises, especially in Africa. The emergence of antimalarial drug resistance continues to be a health problem necessitating an urgent need for alternative and cost-effective antimalarials. Using a molecular hybridization approach, we report the design and synthesis of an efficacious novel class of antiprotozoal agents; (E)-1-(4-(4,6-diphenylpyrimidin-2-yl)piperazin-1-yl)-3-phenyl prop-2-en-1-one derivatives (8a-r). The in vitro inhibitory activity of the synthesized compounds was evaluated against the NF54 chloroquine-sensitive strain of Plasmodium falciparum. From the antiprotozoal screening, three compounds displayed propitious activity with IC50 values (0.18-0.21 μM), using quinine and chloroquine as standard antimalarials. Compounds 8o and 8l emerged as the most potent candidates with IC50 values of 0.18 ± 0.02 μM and 0.21 ± 0.001 μM with an associated good safety index of 18.59 and 16.75 to human kidney epithelial (HEK293) cells, respectively. The synthesized analogues present a new chemical architecture structurally unrelated to the current regime of antimalarial drugs, representing a valid strategy to combat resistance in P. falciparum species to current commercial drugs. We further investigated the binding affinities of the compounds against recombinant forms of two P. falciparum heat shock protein 70 homologues; PfHsp70-1 and PfHsp70-z, both of which are essential and promising druggable candidates. Compound 8l exhibited the highest binding affinity for PfHsp70-1 and PfHsp70-z. Furthermore, molecular docking revealed that compounds 8k, 8l, 8m, and 8o exhibited better fitness to PfHsp70-1, with compounds 8l and 8o showing the highest binding affinity of -10.5 kcal/mol and -10.1 kcal/mol, respectively. Therefore, it can be speculated that PfHsp70-1 may be a possible target of some of the inhibitors tested in this study. The presence of electron-donating groups on the phenyl ring of 4,6-pyrimidine moiety and cinnamoyl group demonstrated a positive correlation between the observed computational data and the biological activity. Taken together, this paper demonstrates the importance of using the molecular hybridization approach in the development of newer cinnamoyl clubbed with 4,6-diphenyl pyrimidine hybrids as potential antiprotozoal agents.

Towards Novel Antiplasmodial Agents-Design, Synthesis and Antimalarial Activity of Second-Generation β-Carboline/Chloroquine Hybrids

As the resistance of Plasmodium to the existing antimalarials increases, there is a crucial need to expand the antimalarial drug pipeline. We recently identified potent antimalarial compounds, namely harmiquins, hybrids derived from the β-carboline alkaloid harmine and 4-amino-7-chloroquinoline, a key structural motif of chloroquine (CQ). To further explore the structure-activity relationship, we synthesised 13 novel hybrid compounds at the position N-9 of the β-carboline ring and evaluated their efficacy in vitro against Plasmodium falciparum 3D7 and Dd2 strains (CQ sensitive and multi-drug resistant, respectively). All compounds exhibit persistent antimalarial activity against both strains of P. falciparum. The most interesting derivatives had low nanomolar activity against both strains (IC50 (33) = 4.7 ± 1.3 nM against Pf3D7 and 6.5 ± 2.5 nM against PfDd2; IC50 (37) = 4.6 ± 0.6 nM against 3D7 and 10.5 ± 0.4 nM against Dd2). Resistance indices (RIs) ranged from 0.9 to 5.3 compared to CQ (RI = 14.4), highlighting their superior consistency in activity against both strains. The cytotoxicity screening performed on HepG2 revealed over 3 orders of magnitude higher IC50 for most of the compounds, with SIs from 711.0 to 8081.8. Spectroscopic studies explored the affinities of newly synthesised compounds for DNA, RNA, and HSA. Both tested hybrids, 34 and 39, were intrinsically fluorescent in an aqueous medium, characterised by remarkable Stokes shifts of emission maxima (Δλ = +103 and +93 nm for 34 and 39, respectively). Fluorimetric experiments revealed that compound 34, with its shorter and more flexible linker, exhibited at least an order of magnitude higher affinity toward ds-DNAs versus ds-RNA and two orders of magnitude higher affinity toward GC-DNAs compared to 39. The behaviour of the investigated compounds upon binding to HSA is very similar, showing a strong hypsochromic shift of the emission maximum (almost Δλ = -70 nm) and demonstrating their effectiveness as fluorimetric probes for distinguishing between DNA/RNA and proteins.

Trend of RTS,S vaccine uptake in the malaria vaccine implementing programme (MVIP) pilot regions, Ghana; 2019-2022

Introduction

The uptake trend of a new vaccine is unpredictable and may reflect the quality of introduction process and community acceptance. The objective of this study was to conduct a trend analysis of RTS,S malaria vaccine uptake in the seven pilot regions of Ghana from 2019 to 2022. The findings are envisaged to strengthen malaria vaccine introductions in the future.

Methods

A retrospective analysis was conducted on routine childhood immunisation data for 2019-2022. Coverages for the first (RTS,S1), second (RTS,S2), third (RTS,S3) and fourth (RTS,S4) doses of malaria vaccine; third dose of diphtheria, tetanus, pertussis-containing vaccine (DTP3/Penta3); first dose measles-rubella (MR1) and second dose measles-rubella (MR2) vaccines were calculated. Dropout rates and uptake gaps were estimated to assess variations in the uptake of consecutive RTS,S schedules; and the differences in the uptake of RTS,S and the comparator vaccines, respectively.

Results

Nationally, the coverages of the first three doses of the RTS,S malaria vaccine rose sharply from 2019 (RTS,S1 = 54.9 %; RTS,S2 = 54.6 %; RTS,S3 = 38.6 %) through 2020 (RTS,S1 = 70.7 %; RTS,S2 = 67.4 %; RTS,S3 = 66.3 %) to peaks in 2021 (RTS,S1 = 76.0 %; RTS,S2 = 73.1 %; RTS,S3 = 74.2 %), and declined marginally in 2022 (RTS,S1 = 74.0 %; RTS,S2 = 69.9 %; RTS,S3 = 71.3 %). For the fourth dose, the low uptake in 2020 (7.5 %) was followed by a steep rise in 2021 (46.9 %) that continued, but at a reduced rate to 50.6% in 2022. The dropout rates and uptake gaps were initially high but declined consistently over the study period. Generally, the trends in vaccination coverages, and dropout rates and uptake gaps at the national level were reflected in the respective regions.

Conclusion

The coverage of RTS,S malaria vaccine improved consistently over the study period despite the low uptake in the early phase of the pilot. While the decreasing dropout rates and uptake gaps may indicate improved community acceptance, strengthening immunisation service delivery is crucial in sustaining the observed trajectory.

Novel Plasmodium falciparum histidine-rich protein 2/3 repeat type in Ethiopian malaria infection: does this affect performance of HRP2-based malaria RDT?

BACKGROUND

Rapid diagnostic tests (RDTs) provide quick, easy, and convenient early diagnosis of malaria ensuring better case management particularly in resource-constrained settings. Nevertheless, the efficiency of HRP2-based RDT can be compromised by Plasmodium falciparum histidine-rich protein 2/3 gene deletion and genetic diversity. This study explored the genetic diversity of PfHRP2/3 in uncomplicated malaria cases from Ethiopia.

METHODS

A cross-sectional study was conducted from June 2022 to March 2023 at Metehara, Zenzelema and Kolla Shele health centres, Ethiopia. Finger-prick blood samples were collected for RDT testing and microscopic examination. For molecular analysis, parasite genomic DNA was extracted from venous blood. Plasmodium falciparum was confirmed using VarATS real time PCR. Additionally, PfHRP2/3 was amplified, and DNA amplicons were sequenced using Oxford Nanopore technology.

RESULTS

PfHRP2/3 sequences revealed small variations in the frequency and number of amino acid repeat types per isolate across the three health centres. Twelve and eight types of amino acid repeats were identified for PfHRP2 and PfHRP3, respectively, which had been previously characterized. Repeat type 1, 4 and 7 were present in both PfHRP2 and PfHRP3 amino acid sequences. Type 2 and 7 repeats were commonly dispersed in PfHRP2, while repeat types 16 and 17 were found only in PfHRP3. A novel 17 V repeat type variant, which has never been reported in Ethiopia, was identified in six PfHRP3 amino acid sequences. The majority of the isolates, as determined by the Baker's logistic regression model, belonged to group C, of which 86% of them were sensitive to PfHRP2-based RDT. Likewise, PfHRP2-based RDT detected 100% of the isolates in group A (product of type 2 × type 7 repeats ≥ 100) and 85.7% in group B (product of types 2 × type 7 repeats 50-99) at a parasitaemia level > 250 parasite/μl.

CONCLUSION

This study highlights the significant diversity observed in PfHRP2 and PfHRP3 among clinical isolates of Plasmodium falciparum in Ethiopia. This emphasizes the necessity for monitoring of PfHRP2- based RDT efficacy and their repeat type distribution using a large sample size and isolates from various ecological settings.

Nanotechnology and malaria: Evaluation of efficacy and toxicity of green nanoparticles and future perspectives

Malaria is a global health problem that causes 1.5-2.7 million deaths worldwide each year. Resistance to antimalarial drugs in malaria parasites and to insecticides in vectors is one of the most serious issues in the fight against this disease. Moreover, the lack of an effective vaccine against malaria is still a major problem. Recent developments in nanotechnology have resulted in new prospects for the fight against malaria, especially by obtaining metal nanoparticles (NPs) that are less toxic, highly biocompatible, environmentally friendly, and less expensive. Numerous studies have been conducted on the synthesis of green NPs using plants and microorganisms (bacteria, fungi, algae, actinomycetes, and viruses). To our knowledge, there is no literature review that compares toxicities and antimalarial effects of some of the existing metallic nanoparticles, revealing their advantages and disadvantages. Hence, the purpose of this work is to assess metal NPs obtained through various green synthesis processes, to display the worth of future malaria research and determine future strategies. Results revealed that there are very few studies on green NPs covering all stages of malaria parasites. Additionally, green metal nanoparticles have yet to be studied for their possible toxic effects on infected as well as healthy erythrocytes. Morever, the toxicities of green metal NPs obtained from various sources differed according to concentration, size, shape, synthesis method, and surface charge, indicating the necessity of optimizing the methods to be used in future studies. It was concluded that studies on the toxic properties of green nanoparticles would be very important for the future.

Reverse N-Substituted Hydroxamic Acid Derivatives of Fosmidomycin Target a Previously Unknown Subpocket of 1-Deoxy-d-xylulose 5-Phosphate Reductoisomerase (DXR)

Reverse analogs of the phosphonohydroxamic acid antibiotic fosmidomycin are potent inhibitors of the nonmevalonate isoprenoid biosynthesis enzyme 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR, IspC) of Plasmodium falciparum. Some novel analogs with large phenylalkyl substituents at the hydroxamic acid nitrogen exhibit nanomolar PfDXR inhibition and potent in vitro growth inhibition of P. falciparum parasites coupled with good parasite selectivity. X-ray crystallographic studies demonstrated that the N-phenylpropyl substituent of the newly developed lead compound 13e is accommodated in a subpocket within the DXR catalytic domain but does not reach the NADPH binding pocket of the N-terminal domain. As shown for reverse carba and thia analogs, PfDXR selectively binds the S-enantiomer of the new lead compound. In addition, some representatives of the novel inhibitor subclass are nanomolar Escherichia coli DXR inhibitors, whereas the inhibition of Mycobacterium tuberculosis DXR is considerably weaker.

Recent advances, challenges and updates on the development of therapeutics for malaria

Malaria has developed as a serious worldwide health issue as a result of the introduction of resistant Plasmodium species strains. Because of the common chemo resistance to most of the existing drugs on the market, it poses a severe health problem and significant obstacles in drug research. Malaria treatment has evolved during the last two decades in response to Plasmodium falciparum drug sensitivity and a return of the disease in tropical areas. Plasmodium falciparum is now highly resistant to the majority of antimalarial drugs. The parasite resistance drew focus to developing novel antimalarials to combat parasite resistance. The requirement for many novel antimalarial drugs in the future year necessitates adopting various drug development methodologies. Different innovative strategies for discovering antimalarial drugs are now being examined here. This review is primarily concerned with the description of newly synthesized antimalarial compounds, i.e. Tafenoquine, Cipargamin, Ferroquine, Artefenomel, DSM265, MMV390048 designed to improve the activity of pure antimalarial enantiomers. In this review, we selected the representative malarial drugs in clinical trials, classified them with detailed targets according to their action, discussed the relationship within the human trials, and generated a summative discussion with prospective expectations.

Evaluating Malaria Rapid Diagnostic Tests and Microscopy for Detecting Plasmodium Infection and Status of Plasmodium falciparum Histidine-Rich Protein 2/3 Gene Deletions in Southeastern Nigeria

Delays in malaria diagnosis increase treatment failures and deaths. In endemic regions, standard diagnostic methods are microscopy and malaria rapid diagnostic tests (mRDTs) detecting Plasmodium falciparum histidine-rich protein 2/3 (PFHRP2/PFHRP3), but gene deletions can allow certain parasites to remain undetected. We enlisted a cohort comprising 207 symptomatic individuals, encompassing both children and adults, at a hospital in Nnewi, Nigeria. The prevalence of parasites was determined using a highly sensitive, species-specific quantitative polymerase chain reaction (SS-qPCR). Within a subset of 132 participants, we assessed the sensitivity and specificity of microscopy and HRP2-mRDTs in comparison to SS-qPCR for the detection of P. falciparum. We also investigated the prevalence of pfhrp2/pfhrp3 gene deletions. Greater sensitivity was achieved with mRDTs (95%) compared with microscopy (77%). Also, mRDTs exhibited greater specificity (68%) than microscopy (44%). The positive predictive value of mRDTs (89%) surpassed that of microscopy (80%), suggesting a greater probability of accurately indicating the presence of infection. The negative predictive value of mRDTs (82%) was far greater than microscopy (39%). Of the 165 P. falciparum-positive samples screened for pfhrp2/pfhrp3 gene deletions, one gene deletion was detected in one sample. Regarding infection prevalence, 84% were positive for Plasmodium spp. (by reverse transcription [RT]-qPCR), with P. falciparum responsible for the majority (97%) of positive cases. Thus, exclusive reliance on microscopy in endemic areas may impede control efforts resulting from false negatives, underscoring the necessity for enhanced training and advocating for high-throughput molecular testing such as RT-qPCR or qPCR at referral centers to address limitations.

A comprehensive review of synthetic strategies and SAR studies for the discovery of PfDHODH inhibitors as antimalarial agents. Part 1: triazolopyrimidine, isoxazolopyrimidine and pyrrole-based (DSM) compounds

One of the deadliest infectious diseases, malaria, still has a significant impact on global morbidity and mortality. Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) catalyzes the fourth step in de novo pyrimidine nucleotide biosynthesis and has been clinically validated as an innovative and promising target for the development of novel targeted antimalarial drugs. PfDHODH inhibitors have the potential to significantly slow down parasite growth at the blood and liver stages. Several PfDHODH inhibitors based on various scaffolds have been explored over the past two decades. Among them, triazolopyrimidines, isoxazolopyrimidines, and pyrrole-based derivatives known as DSM compounds showed tremendous potential as novel antimalarial agents, and one of the triazolopyrimidine-based compounds (DSM265) was able to reach phase IIa clinical trials. DSM compounds were synthesized as PfDHODH inhibitors with various substitutions based on structure-guided medicinal chemistry approaches and further optimised as well. For the first time, this review provides an overview of all the synthetic approaches used for the synthesis, alternative synthetic routes, and novel strategies involving various catalysts and chemical reagents that have been used to synthesize DSM compounds. We have also summarized SAR study of all these PfDHODH inhibitors. In an attempt to assist readers, scientists, and researchers involved in the development of new PfDHODH inhibitors as antimalarials, this review provides accessibility of all synthetic techniques and SAR studies of the most promising triazolopyrimidines, isoxazolopyrimidines, and pyrrole-based PfDHODH inhibitors.

In Silico Approach Triterpene Glycoside of H. atra Targeting Orotidine 5-Monophosphate Decarboxylase Protein (PfOMPDC) in P. falciparum Infection Mechanism

This study accessed the potential antimalarial activity of triterpene glycoside of H. atra through targeting orotidine 5-monophosphate decarboxylase protein (PfOMPDC) in P. falciparum by molecular docking. Nine triterpene glycosides from H. atra extract modeled the structure by the Corina web server and interacted with PfOMPDC protein by using Hex 8.0.0. The docking results were visualized and analyzed by Discovery Studio version 21.1.1. 17-Hydroxyfuscocineroside B showed the lowest binding energy in PfOMPDC interaction, which was -1,098.13 kJ/mol. Holothurin A3, echinoside A, and fuscocineroside C showed low binding energy. Nine triterpene glycosides of H. atra performed interaction with PfOMPDC protein at the same region. Holothurin A1 posed interaction with PfOMPDC protein by 8 hydrogen bonds, 3 hydrophobic interactions, and 8 unfavorable bonds. Several residues were detected in the same active sites of other triterpene glycosides. Residue TYR111 was identified in all triterpene glycoside complexes, except holothurin A3 and calcigeroside B. In summary, the triterpene glycoside of H. atra is potentially a drug candidate for malaria therapeutic agents. In vitro and in vivo studies were required for further investigation.

Design and Evaluation of Chimeric Plasmodium falciparum Circumsporozoite Protein-Based Malaria Vaccines

Efficacy data on two malaria vaccines, RTS,S and R21, targeting Plasmodium falciparum circumsporozoite protein (PfCSP), are encouraging. Efficacy may be improved by induction of additional antibodies to neutralizing epitopes outside of the central immunodominant repeat domain of PfCSP. We designed four rPfCSP-based vaccines in an effort to improve the diversity of the antibody response. We also evaluated P. falciparum merozoite surface protein 8 (PfMSP8) as a malaria-specific carrier protein as an alternative to hepatitis B surface antigen. We measured the magnitude, specificity, subclass, avidity, durability, and efficacy of vaccine-induced antibodies in outbred CD1 mice. In comparison to N-terminal- or C-terminal-focused constructs, immunization with near full-length vaccines, rPfCSP (#1) or the chimeric rPfCSP/8 (#2), markedly increased the breadth of B cell epitopes recognized covering the N-terminal domain, junctional region, and central repeat. Both rPfCSP (#1) and rPfCSP/8 (#2) also elicited a high proportion of antibodies to conformation-dependent epitopes in the C-terminus of PfCSP. Fusion of PfCSP to PfMSP8 shifted the specificity of the T cell response away from PfCSP toward PfMSP8 epitopes. Challenge studies with transgenic Plasmodium yoelii sporozoites expressing PfCSP demonstrated high and consistent sterile protection following rPfCSP/8 (#2) immunization. Of note, antibodies to conformational C-terminal epitopes were not required for protection. These results indicate that inclusion of the N-terminal domain of PfCSP can drive responses to protective, repeat, and non-repeat B cell epitopes and that PfMSP8 is an effective carrier for induction of high-titer, durable anti-PfCSP antibodies.

PRL2 regulates neutrophil extracellular trap formation which contributes to severe malaria and acute lung injury

Excessive host immune responses contribute to severe malaria with high mortality. Here, we show that PRL2 in innate immune cells is highly related to experimental malaria disease progression, especially the development of murine severe malaria. In the absence of PRL2 in myeloid cells, Plasmodium berghei infection results in augmented lung injury, leading to significantly increased mortality. Intravital imaging revealed greater neutrophilic inflammation and NET formation in the lungs of PRL2 myeloid conditional knockout mice. Depletion of neutrophils prior to the onset of severe disease protected mice from NETs associated lung injury, and eliminated the difference between WT and PRL2 CKO mice. PRL2 regulates neutrophil activation and NET accumulation via the Rac-ROS pathway, thus contributing to NETs associated ALI. Hydroxychloroquine, an inhibitor of PRL2 degradation alleviates NETs associated tissue damage in vivo. Our findings suggest that PRL2 serves as an indicator of progression to severe malaria and ALI. In addition, our study indicated the importance of PRL2 in NET formation and tissue injury. It might open a promising path for adjunctive treatment of NET-associated disease.

Administration of ivermectin to cattle induced mortality, reduced fecundity and survivorship of Anopheles arabiensis in Ethiopia: an implication for expansion of vector control toolbox

BACKGROUND

Although many countries have shown interest in eliminating malaria, approaches that complement existing vector control interventions are needed because existing methods have been scaled up but malaria still persists. Therefore, the effect of ivermectin administration to cattle was evaluated for its effect on mortality, survivorship and mortality of laboratory reared Anopheles arabiensis.

METHODS

Three calves were randomly selected and injected with ivermectin at a therapeutic dose of 0.2 mg/kg, while the other two calves received no treatment and served as controls. Five tents were constructed for the trial. Calves were housed in tents (one per tent) and then 30 starved female An. arabiensis were introduced into each tent. Only fully engorged females were collected from each tent and placed in different mosquito cages to monitor their mortality, survival and fecundity. Data analysis was done using SPSS version 16.

RESULTS

During the follow-up period (until day 21), ivermectin induced significantly higher mortality when compared to controls. It resulted in an average 24-h mortality rate of 81.6% against An. arabiensis on the first day following treatment. 100% An. arabiensis that fed on ivermectin-treated calves on the first day after treatment died within four days. Egg production rate of An. arabiensis that fed on ivermectin-treated calves was significantly lower compared to controls (F = 768.7, P < 0.001).

CONCLUSION

In conclusion, ivermectin induced mortality, reduced fecundity and survivorship of laboratory maintained An. arabiensis. Further study is recommended using a wild mosquito population. Moreover, mass ivermectin administration to domestic animals could be recommended to supplement the existing indoor based interventions.

Design, synthesis and modelling of photoreactive chemical probes for investigating target engagement of plasmepsin IX and X in Plasmodium falciparum

The emergence of Plasmodium parasite resistance to current front-line antimalarial treatments poses a serious threat to global malaria control and highlights the necessity for the development of therapeutics with novel targets and mechanisms of action. Plasmepsins IX and X (PMIX/PMX) have been recognised as highly promising targets in Plasmodium due to their contribution to parasite's pathogenicity. Recent research has demonstrated that dual PMIX/PMX inhibition results in the impairment of multiple parasite's life cycle stages, which is an important feature in drug resistance prevention. Herein we report novel hydroxyethylamine photoaffinity labelling (PAL) probes, designed for PMIX/PMX target engagement and proteomics experiments in Plasmodium parasites. The prepared probes have both a photoreactive group (diazirine or benzophenone) for covalent attachment to target proteins, and a terminal alkyne handle allowing their use in bioorthogonal ligation. One of the synthesised benzophenone probes was shown to be highly promising as demonstrated by its outstanding antimalarial potency (IC50 = 15 nM versus D10 P. falciparum) and its inhibitory effect against PfPMX in an enzymatic assay. Molecular docking and molecular dynamics studies show that the inclusion of the benzophenone and alkyne handle does not alter the binding mode compared to the parent compound. The photoaffinity probe can be used in future chemical proteomics studies to allow hydroxyethylamine drug scaffold target identification and validation in Plasmodium. We expect our findings to act as a tool for future investigations on PMIX/PMX inhibition in antimalarial drug discovery.

A Review on Synthetic Thiazole Derivatives as an Antimalarial Agent

BACKGROUND

Thiazole is a widely studied core structure in heterocyclic chemistry and has proven to be a valuable scaffold in medicinal chemistry. The presence of thiazole in both naturally occurring and synthetic pharmacologically active compounds demonstrates the adaptability of these derivatives.

METHODS

The current study attempted to review and compile the contributions of numerous researchers over the last 20 years to the medicinal importance of these scaffolds, with a primary focus on antimalarial activity. The review is based on an extensive search of PubMed, Google Scholar, Elsevier, and other renowned journal sites for a thorough literature survey involving various research and review articles.

RESULTS

A comprehensive review of the antimalarial activity of the thiazole scaffold revealed potential therapeutic targets in Plasmodium species. Furthermore, the correlation of structure-activity-relationship (SAR) studies from various articles suggests that the thiazole ring has therapeutic potential.

CONCLUSION

This article intends to point researchers in the right direction for developing potential thiazole-based compounds as antimalarial agents in the future.

Immune mechanisms targeting malaria transmission: opportunities for vaccine development

INTRODUCTION

Malaria continues to remain a major global health problem with nearly a quarter of a billion clinical cases and more than 600,000 deaths in 2022. There has been significant progress toward vaccine development, however, poor efficacy of approved vaccines requiring multiple immunizing doses emphasizes the need for continued efforts toward improved vaccines. Progress to date, nonetheless, has provided impetus for malaria elimination.

AREAS COVERED

In this review we will focus on diverse immune mechanisms targeting gametocytes in the human host and gametocyte-mediated malaria transmission via the mosquito vector.

EXPERT OPINION

To march toward the goal of malaria elimination it will be critical to target the process of malaria transmission by mosquitoes, mediated exclusively by the sexual stages, i.e. male, and female gametocytes, ingested from infected vertebrate host. Studies over several decades have established antigens in the parasite sexual stages developing in the mosquito midgut as attractive targets for the development of transmission blocking vaccines (TBVs). Immune clearance of gametocytes in the vertebrate host can synergize with TBVs and directly aid in maintaining effective transmission reducing immune potential.

Mosquito-borne diseases in India over the past 50 years and their Global Public Health Implications: A Systematic Review

Mosquito-borne diseases (MBDs) pose a significant public health concern globally, and India, with its unique eco-sociodemographic characteristics, is particularly vulnerable to these diseases. This comprehensive review aims to provide an in-depth overview of MBDs in India, emphasizing their impact and potential implications for global health. The article explores distribution, epidemiology, control or elimination, and economic burden of the prevalent diseases such as malaria, dengue, chikungunya, Japanese encephalitis, and lymphatic filariasis, which collectively contribute to millions of cases annually. It sheds light on their profound effects on morbidity, mortality, and socioeconomic burdens and the potential for international transmission through travel and trade. The challenges and perspectives associated with controlling mosquito populations are highlighted, underscoring the importance of effective public health communication for prevention and early detection. The potential for these diseases to spread beyond national borders is recognized, necessitating a holistic approach to address the challenge. A comprehensive literature search was conducted, covering the past five decades (1972-2022), utilizing databases such as Web of Science, PubMed, and Google Scholar, in addition to in-person library consultations. The literature review analyzed 4,082 articles initially identified through various databases. After screening and eligibility assessment, 252 articles were included for analysis. The review focused on malaria, dengue, chikungunya, Japanese encephalitis, and lymphatic filariasis. The included studies focused on MBDs occurrence in India, while those conducted outside India, lacking statistical analysis, or published before 1970 were excluded. This review provides valuable insights into the status of MBDs in India and underscores the need for concerted efforts to combat these diseases on both national and global scales through consilience.

Administration of soluble gp130Fc disrupts M-1 macrophage polarization, dendritic cell activation, MDSC expansion and Th-17 induction during experimental cerebral malaria

Regulatory effect of IL-6 on various immune cells plays a crucial role during experimental cerebral malaria pathogenesis. IL-6 neutralization can restore distorted ratios of myeloid dendritic cells and plasmacytoid dendritic cells as well as the balance between Th-17 and T-regulatory cells. IL-6 can also influence immune cells through classical and trans IL-6 signalling pathways. As trans IL-6 signalling is reportedly involved during malaria pathogenesis, we focused on studying the effects of trans IL-6 signalling blockade on various immune cell populations and how they regulate ECM progression. Results show that administration of sgp130Fc recombinant chimera protein lowers the parasitemia, increases the survivability of Plasmodium berghei ANKA infected mice, and restores the distorted ratios of M1/M2 macrophage, mDC/pDC, and Th-17/Treg. IL-6 trans signalling blockade has been found to affect both expansion of myeloid derived suppressor cells (MDSCs) and expression of inflammatory markers on them during Plasmodium berghei ANKA infection indicating that trans IL-6 signalling might regulate various immune cells and their function during ECM. In this work for the first time, we delineate the effect of sgp130Fc administration on influencing the immunological changes within the host secondary lymphoid organ during ECM induced by Plasmodium berghei ANKA infection.

Mechanistic insights into the interaction between the host gut microbiome and malaria

Malaria is a devastating infectious disease and significant global health burden caused by the bite of a Plasmodium-infected female Anopheles mosquito. Gut microbiota was recently discovered as a risk factor of severe malaria. This review entails the recent advances on the impact of gut microbiota composition on malaria severity and consequence of malaria infection on gut microbiota in mammalian hosts. Additionally, this review provides mechanistic insight into interactions that might occur between gut microbiota and host immunity which in turn can modulate malaria severity. Finally, approaches to modulate gut microbiota composition are discussed. We anticipate this review will facilitate novel hypotheses to move the malaria-gut microbiome field forward.

Structure-Activity Relationships and Antiplasmodial Potencies of Novel 3,4-Disubstituted 1,2,5-Oxadiazoles

The 4-substituted 3-amino-1,2,5-oxadiazole 1 from the Malaria Box Project of the Medicines for Malaria Venture foundation shows very promising selectivity and in vitro activity against Plasmodium falciparum. Within the first series of new compounds, various 3-acylamino analogs were prepared. This paper now focuses on the investigation of the importance of the aromatic substituent in ring position 4. A number of new structure-activity relationships were elaborated, showing that antiplasmodial activity and selectivity strongly depend on the substitution pattern of the 4-phenyl moiety. In addition, physicochemical parameters relevant for drug development were calculated (logP and ligand efficiency) or determined experimentally (CYP3A4-inhibition and aqueous solubility). N-[4-(3-ethoxy-4-methoxyphenyl)-1,2,5-oxadiazol-3-yl]-3-methylbenzamide 51 showed high in vitro activity against the chloroquine-sensitive strain NF54 of P. falciparum (PfNF54 IC50 = 0.034 µM), resulting in a very promising selectivity index of 1526.

Manual correction of genome annotation improved alternative splicing identification of Artemisia annua

Gene annotation is essential for genome-based studies. However, algorithm-based genome annotation is difficult to fully and correctly reveal genomic information, especially for species with complex genomes. Artemisia annua L. is the only commercial resource of artemisinin production though the content of artemisinin is still to be improved. Genome-based genetic modification and breeding are useful strategies to boost artemisinin content and therefore, ensure the supply of artemisinin and reduce costs, but better gene annotation is urgently needed. In this study, we manually corrected the newly released genome annotation of A. annua using second- and third-generation transcriptome data. We found that incorrect gene information may lead to differences in structural, functional, and expression levels compared to the original expectations. We also identified alternative splicing events and found that genome annotation information impacted identifying alternative splicing genes. We further demonstrated that genome annotation information and alternative splicing could affect gene expression estimation and gene function prediction. Finally, we provided a valuable version of A. annua genome annotation and demonstrated the importance of gene annotation in future research.

Tackling the emerging Artemisinin-resistant malaria parasite by modulation of defensive oxido-reductive mechanism via nitrofurantoin repurposing

Oxidative stress-mediated cell death has remained the prime parasiticidal mechanism of front line antimalarial, artemisinin (ART). The emergence of resistant Plasmodium parasites characterized by oxidative stress management due to impaired activation of ART and enhanced reactive oxygen species (ROS) detoxification has decreased its clinical efficacy. This gap can be filled by development of alternative chemotherapeutic agents to combat resistance defense mechanism. Interestingly, repositioning of clinically approved drugs presents an emerging approach for expediting antimalarial drug development and circumventing resistance. Herein, we evaluated the antimalarial potential of nitrofurantoin (NTF), a clinically used antibacterial drug, against intra-erythrocytic stages of ART-sensitive (Pf3D7) and resistant (PfKelch13R539T) strains of P. falciparum, alone and in combination with ART. NTF exhibited growth inhibitory effect at submicro-molar concentration by arresting parasite growth at trophozoite stage. It also inhibited the survival of resistant parasites as revealed by ring survival assay. Concomitantly, in vitro combination assay revealed synergistic association of NTF with ART. NTF was found to enhance the reactive oxygen and nitrogen species, and induced mitochondrial membrane depolarization in parasite. Furthermore, we found that exposure of parasites to NTF disrupted redox balance by impeding Glutathione Reductase activity, which manifests in enhanced oxidative stress, inducing parasite death. In vivo administration of NTF, alone and in combination with ART, in P. berghei ANKA-infected mice blocked parasite multiplication and enhanced mean survival time. Overall, our results indicate NTF as a promising repurposable drug with therapeutic potential against ART-sensitive as well as resistant parasites.

Biphosphoglycerate Mutase: A Novel Therapeutic Target for Malaria?

Biphosphoglycerate mutase (BPGM) is a tri-functional enzyme expressed exclusively in erythroid cells and tissues that is responsible for the production of 2,3-biphosphoglycerate (2,3-BPG) through the Rapoport-Luebering shunt. The 2,3-BPG is required for efficient glycolysis and ATP production under anaerobic conditions, but is also a critical allosteric regulator of hemoglobin (Hb), acting to regulate oxygen release in peripheral tissues. In humans, BPGM deficiency is very rare, and is associated with reduced levels of erythrocytic 2,3-BPG and ATP, left shifted Hb-O2 dissociation curve, low P50, elevated Hb and constitutive erythrocytosis. BPGM deficiency in mice recapitulates the erythroid defects seen in human patients. A recent report has shown that BPGM deficiency in mice affords striking protection against both severe malaria anemia and cerebral malaria. These findings are reminiscent of studies of another erythrocyte specific glycolytic enzyme, Pyruvate Kinase (PKLR), which mutational inactivation protects humans and mice against malaria through impairment of glycolysis and ATP production in erythrocytes. BPGM, and PKLR join glucose-6-phosphate dehydrogenase (G6PD) and other erythrocyte variants as modulating response to malaria. Recent studies reviewed suggest glycolysis in general, and BPGM in particular, as a novel pharmacological target for therapeutic intervention in malaria.

Regulatory Functions of Hypoxia in Host-Parasite Interactions: A Focus on Enteric, Tissue, and Blood Protozoa

Body tissues are subjected to various oxygenic gradients and fluctuations and hence can become transiently hypoxic. Hypoxia-inducible factor (HIF) is the master transcriptional regulator of the cellular hypoxic response and is capable of modulating cellular metabolism, immune responses, epithelial barrier integrity, and local microbiota. Recent reports have characterized the hypoxic response to various infections. However, little is known about the role of HIF activation in the context of protozoan parasitic infections. Growing evidence suggests that tissue and blood protozoa can activate HIF and subsequent HIF target genes in the host, helping or hindering their pathogenicity. In the gut, enteric protozoa are adapted to steep longitudinal and radial oxygen gradients to complete their life cycle, yet the role of HIF during these protozoan infections remains unclear. This review focuses on the hypoxic response to protozoa and its role in the pathophysiology of parasitic infections. We also discuss how hypoxia modulates host immune responses in the context of protozoan infections.

Medicinal plants used for treatment of malaria by indigenous communities of Tororo District, Eastern Uganda

BACKGROUND

Malaria remains the leading cause of death in sub-Saharan Africa. Although recent developments such as malaria vaccine trials inspire optimism, the search for novel antimalarial drugs is urgently needed to control the mounting resistance of Plasmodium species to the available therapies. The present study was conducted to document ethnobotanical knowledge on the plants used to treat symptoms of malaria in Tororo district, a malaria-endemic region of Eastern Uganda.

METHODS

An ethnobotanical study was carried out between February 2020 and September 2020 in 12 randomly selected villages of Tororo district. In total, 151 respondents (21 herbalists and 130 non-herbalists) were selected using multistage random sampling method. Their awareness of malaria, treatment-seeking behaviour and herbal treatment practices were obtained using semi-structured questionnaires and focus group discussions. Data were analysed using descriptive statistics, paired comparison, preference ranking and informant consensus factor.

RESULTS

A total of 45 plant species belonging to 26 families and 44 genera were used in the preparation of herbal medicines for management of malaria and its symptoms. The most frequently mentioned plant species were Vernonia amygdalina, Chamaecrista nigricans, Aloe nobilis, Warburgia ugandensis, Abrus precatorius, Kedrostis foetidissima, Senna occidentalis, Azadirachta indica and Mangifera indica. Leaves (67.3%) were the most used plant part while maceration (56%) was the major method of herbal remedy preparation. Oral route was the predominant mode of administration with inconsistencies in the posology prescribed.

CONCLUSION

This study showed that the identified medicinal plants in Tororo district, Uganda, are potential sources of new antimalarial drugs. This provides a basis for investigating the antimalarial efficacy, phytochemistry and toxicity of the unstudied species with high percentage use values to validate their use in the management of malaria.

Magnitude and patterns of severe Plasmodium vivax monoinfection in Vietnam: a 4-year single-center retrospective study

Introduction

Infection with Plasmodium vivax is a recognized cause of severe malaria including deaths. The exact burden and patterns of severe P. vivax monoinfections is however still not well quantified, especially in P. vivax endemic regions. We examined the magnitude and patterns of severe malaria caused by monoinfections of P. vivax and associated predictors among patients admitted to a tertiary care center for malaria in Vietnam.

Methods

A retrospective cohort study was conducted based on the patients' medical records at the Hospital for Tropical Diseases from January 2015 to December 2018. Extracted information included demographic, epidemiologic, clinical, laboratory and treatment characteristics.

Results

Monoinfections with P. vivax were found in 153 (34.5, 95% CI 30.3-39.1%) patients of whom, uncomplicated and severe malaria were documented in 89.5% (137/153, 95% CI 83.7-93.5%) and 10.5% (16/153, 95% CI 6.5-16.3%), respectively. Patterns of severe malaria included jaundice (8 cases), hypoglycemia (3 cases), shock (2 cases), anemia (2 cases), and cerebral malaria (1 case). Among 153 patients, 73 (47.7%) had classic malaria paroxysm, 57 (37.3%) had >7 days of illness at the time of admission, and 40 (26.1%) were referred from other hospitals. A misdiagnosis as having other diseases from malaria cases coming from other hospitals was up to 32.5% (13/40). Being admitted to hospital after day 7th of illness (AOR = 6.33, 95% CI 1.14-35.30, p = 0.035) was a predictor of severe malaria. Severe malaria was statistically associated with longer hospital length of stay (p = 0.035). Early and late treatment failures and recrudescence were not recorded. All patients recovered completely.

Discussion

This study confirms the emergence of severe vivax malaria in Vietnam which is associated with delayed hospital admission and increased hospital length of stay. Clinical manifestations of P. vivax infection can be misdiagnosed which results in delayed treatment. To meet the goal of malaria elimination by 2030, it is crucial that the non-tertiary hospitals have the capacity to quickly and correctly diagnose malaria and then provide treatment for malaria including P. vivax infections. More robust studies need to be conducted to fully elucidate the magnitude of severe P. vivax in Vietnam.

Safe drugs with high potential to block malaria transmission revealed by a spleen-mimetic screening

Malaria parasites like Plasmodium falciparum multiply in red blood cells (RBC), which are cleared from the bloodstream by the spleen when their deformability is altered. Drug-induced stiffening of Plasmodium falciparum-infected RBC should therefore induce their elimination from the bloodstream. Here, based on this original mechanical approach, we identify safe drugs with strong potential to block the malaria transmission. By screening 13 555 compounds with spleen-mimetic microfilters, we identified 82 that target circulating transmissible form of P. falciparum. NITD609, an orally administered PfATPase inhibitor with known effects on P. falciparum, killed and stiffened transmission stages in vitro at nanomolar concentrations. Short exposures to TD-6450, an orally-administered NS5A hepatitis C virus inhibitor, stiffened transmission parasite stages and killed asexual stages in vitro at high nanomolar concentrations. A Phase 1 study in humans with a primary safety outcome and a secondary pharmacokinetics outcome ( https://clinicaltrials.gov , ID: NCT02022306) showed no severe adverse events either with single or multiple doses. Pharmacokinetic modelling showed that these concentrations can be reached in the plasma of subjects receiving short courses of TD-6450. This physiologically relevant screen identified multiple mechanisms of action, and safe drugs with strong potential as malaria transmission-blocking agents which could be rapidly tested in clinical trials.

A Critical Review on Human Malaria and Schistosomiasis Vaccines: Current State, Recent Advancements, and Developments

Malaria and schistosomiasis are two major parasitic diseases that remain leading causes of morbidity and mortality worldwide. Co-infections of these two parasites are common in the tropics, where both diseases are endemic. The clinical consequences of schistosomiasis and malaria are determined by a variety of host, parasitic, and environmental variables. Chronic schistosomiasis causes malnutrition and cognitive impairments in children, while malaria can cause fatal acute infections. There are effective drugs available to treat malaria and schistosomiasis. However, the occurrence of allelic polymorphisms and the rapid selection of parasites with genetic mutations can confer reduced susceptibility and lead to the emergence of drug resistance. Moreover, the successful elimination and complete management of these parasites are difficult due to the lack of effective vaccines against Plasmodium and Schistosoma infections. Therefore, it is important to highlight all current vaccine candidates undergoing clinical trials, such as pre-erythrocytic and erythrocytic stage malaria, as well as a next-generation RTS,S-like vaccine, the R21/Matrix-M vaccine, that conferred 77% protection against clinical malaria in a Phase 2b trial. Moreover, this review also discusses the progress and development of schistosomiasis vaccines. Furthermore, significant information is provided through this review on the effectiveness and progress of schistosomiasis vaccines currently under clinical trials, such as Sh28GST, Sm-14, and Sm-p80. Overall, this review provides insights into recent progress in malarial and schistosomiasis vaccines and their developmental approaches.

Significance of Plasmodium berghei Amino Acid Transporter 1 in Food Vacuole Functionality and Its Association with Cerebral Pathogenesis

The food vacuole plays a central role in the blood stage of parasite development by digesting host hemoglobin acquired from red blood cells and detoxifying the host heme released during hemoglobin digestion into hemozoin. Blood-stage parasites undergo periodic schizont bursts, releasing food vacuoles containing hemozoin. Clinical studies in malaria-infected patients and in vivo animal studies have shown the association of hemozoin with disease pathogenesis and abnormal host immune responses in malaria. Here, we perform a detailed in vivo characterization of putative Plasmodium berghei amino acid transporter 1 localized in the food vacuole to understand its significance in the malaria parasite. We show that the targeted deletion of amino acid transporter 1 in Plasmodium berghei leads to a swollen food vacuole phenotype with the accumulation of host hemoglobin-derived peptides. Plasmodium berghei amino acid transporter 1-knockout parasites produce less hemozoin, and the hemozoin crystals display a thin morphology compared with wild-type parasites. The knockout parasites show reduced sensitivity to chloroquine and amodiaquine by showing recrudescence. More importantly, mice infected with the knockout parasites are protected from cerebral malaria and display reduced neuronal inflammation and cerebral complications. Genetic complementation of the knockout parasites restores the food vacuole morphology with hemozoin levels similar to that of wild-type parasites, causing cerebral malaria in the infected mice. The knockout parasites also show a significant delay in male gametocyte exflagellation. Our findings highlight the significance of amino acid transporter 1 in food vacuole functionality and its association with malaria pathogenesis and gametocyte development. IMPORTANCE Food vacuoles of the malaria parasite are involved in the degradation of red blood cell hemoglobin. The amino acids derived from hemoglobin degradation support parasite growth, and the heme released is detoxified into hemozoin. Antimalarials such as quinolines target hemozoin formation in the food vacuole. Food vacuole transporters transport hemoglobin-derived amino acids and peptides from the food vacuole to the parasite cytosol. Such transporters are also associated with drug resistance. Here, we show that the deletion of amino acid transporter 1 in Plasmodium berghei leads to swollen food vacuoles with the accumulation of hemoglobin-derived peptides. The transporter-deleted parasites generate less hemozoin with thin crystal morphology and show reduced sensitivity to quinolines. Mice infected with transporter-deleted parasites are protected from cerebral malaria. There is also a delay in male gametocyte exflagellation, affecting transmission. Our findings uncover the functional significance of amino acid transporter 1 in the life cycle of the malaria parasite.

Targeting plasmodium α-tubulin-1 to block malaria transmission to mosquitoes

Plasmodium ookinetes use an invasive apparatus to invade mosquito midguts, and tubulins are the major structural proteins of this apical complex. We examined the role of tubulins in malaria transmission to mosquitoes. Our results demonstrate that the rabbit polyclonal antibodies (pAb) against human α-tubulin significantly reduced the number of P. falciparum oocysts in Anopheles gambiae midguts, while rabbit pAb against human β-tubulin did not. Further studies showed that pAb, specifically against P. falciparum α-tubulin-1, also significantly limited P. falciparum transmission to mosquitoes. We also generated mouse monoclonal antibodies (mAb) using recombinant P. falciparum α-tubulin-1. Out of 16 mAb, two mAb, A3 and A16, blocked P. falciparum transmission with EC50 of 12 μg/ml and 2.8 μg/ml. The epitopes of A3 and A16 were determined to be a conformational and linear sequence of EAREDLAALEKDYEE, respectively. To understand the mechanism of the antibody-blocking activity, we studied the accessibility of live ookinete α-tubulin-1 to antibodies and its interaction with mosquito midgut proteins. Immunofluorescent assays showed that pAb could bind to the apical complex of live ookinetes. Moreover, both ELISA and pull-down assays demonstrated that insect cell-expressed mosquito midgut protein, fibrinogen-related protein 1 (FREP1), interacts with P. falciparum α-tubulin-1. Since ookinete invasion is directional, we conclude that the interaction between Anopheles FREP1 protein and Plasmodium α-tubulin-1 anchors and orients the ookinete invasive apparatus towards the midgut PM and promotes the efficient parasite infection in the mosquito.

An in silico quest for next-generation antimalarial drugs by targeting Plasmodium falciparum hexose transporter protein: a multi-pronged approach

The emergence of artemisinin resistance by malaria parasites is a major challenge in the fight against malaria, thus posing serious threat to the public health across the world. To tackle this, antimalarial drugs with unconventional mechanisms are therefore urgently needed. It has been reported that selective starvation of Plasmodium falciparum by blocking the function of hexose transporter 1 (PfHT1) protein, the only known transporter for glucose uptake in P. falciparum, could provide an alternative approach to fight the drug resistant malaria parasites. In this study, three high affinity molecules (BBB_25784317, BBB_26580136 and BBB_26580144) that have shown the best docked conformation and least binding energy with PfHT1 were shortlisted. The docking energy of BBB_25784317, BBB_26580136 and BBB_26580144 with PfHT1 were -12.5, -12.1 and -12.0 kcal/mol, respectively. In the follow up simulation studies, the protein 3D structure maintains considerable stability in the presence of the compounds. It was also observed that the compounds produced a number of hydrophilic and hydrophobic interactions with the protein allosteric site residues. This demonstrates strong intermolecular interaction guided by close distance hydrogen bonds of compounds with Ser45, Asn48, Thr49, Asn52, Ser317, Asn318, Ile330 and Ser334. Revalidation of compounds binding affinity was conducted by more appropriate simulation based binding free energy techniques (MM-GB/PBSA and WaterSwap). Additionally, entropy assay was performed that further strengthen the predictions. In silico pharmacokinetics confirmed that the compounds would be suitable candidates for oral delivery due to their high gastrointestinal absorption and less toxic reaction. Overall, the predicted compounds are promising and could be further sought as antimalarial leads and subjected to thorough experimental investigations.Communicated by Ramaswamy H. Sarma.

Heparin-Coated Dendronized Hyperbranched Polymers for Antimalarial Targeted Delivery

The rampant evolution of resistance in Plasmodium to all existing antimalarial drugs calls for the development of improved therapeutic compounds and of adequate targeted delivery strategies for them. Loading antimalarials in nanocarriers specifically targeted to the parasite will contribute to the administration of lower overall doses, with reduced side effects for the patient, and of higher local amounts to parasitized cells for an increased lethality toward the pathogen. Here, we report the development of dendronized hyperbranched polymers (DHPs), with capacity for antimalarial loading, that are coated with heparin for their specific targeting to red blood cells parasitized by Plasmodium falciparum. The resulting DHP-heparin complexes exhibit the intrinsic antimalarial activity of heparin, with an IC50 of ca. 400 nM, added to its specific targeting to P. falciparum-infected (vs noninfected) erythrocytes. DHP-heparin nanocarriers represent a potentially interesting contribution to the limited family of structures described so far for the loading and targeted delivery of current and future antimalarial compounds.

Highly N-Methylated Peptides from the Antarctic Sponge Inflatella coelosphaeroides Are Active against Plasmodium falciparum

Malaria, caused by the parasite Plasmodium falciparum, continues to threaten much of the world's population, and there is a pressing need for expanding treatment options. Natural products have been a vital source of such drugs, and here we report seven new highly N-methylated linear peptides, friomaramide B (2) and shagamides A-F (3-8) from the marine sponge Inflatella coelosphaeroides, collected in Antarctic waters, which demonstrate activity against three strains of blood-stage P. falciparum. The planar structures of these metabolites were solved by interpreting NMR data, as well as HRESIMS/MS fragmentation patterns, while Marfey's analysis was used to establish the configurations of the amino acids. Reisolation of the previously reported compound friomaramide A (1) allowed us to revise its structure. The panel of isolated compounds allowed establishing structure/activity relationships and provided information for future structure optimization for this class of P. falciparum inhibitory metabolites.

In Vitro and in Vivo Evaluation of the Antimalarial Activities of Kniphofia reflexa Hutchinson ex Codd

In a phytochemical investigation of the rhizomes of Kniphofia reflexa, an endemic plant used to treat relapsing fevers in Kejom, northwestern Cameroon, 12 known (1-12) compounds were obtained following chromatographic methods and purification, together with 3 new derivatives (13-15) prepared by acetylation. One-dimensional and 2-dimensional nuclear magnetic resonance spectroscopic studies together with infrared and ultraviolet spectral analyses in association with data found in the literature were used to determine the structure of the compounds. In the in vitro evaluation of compounds 1-9, 12-14, and the crude extract against Plasmodium falciparum chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains, cassiamin C (1) [IC50 0.57 ± 0.54 (D6); 0.78 ± 0.08 (W2)], and crude extract [IC50 1.06 ± 0.22 (D6); 1.08 ± 0.12 (W2)] were highly active against the parasites. Kniphofiarexine (12) was inactive. However, its derivative, kniphofiarexine B (14), was moderately active. In the in vivo studies, the extract suppressed Plasmodium berghei growth, but did not clear completely the parasites.

Increasing challenges of malaria control in sub-Saharan Africa: Priorities for public health research and policymakers

The ever-increasing cases and mortality due to malaria remains one of the most important public health threats, especially in sub-Saharan Africa-where this burden is considerably high. In 2020, sub-Saharan Africa accounted for about 95% of all cases and 96% of all malaria deaths with about 80% of these deaths reported in children under the age of 5. This review, adopting a public health focus, aimed to understand the challenges of malaria control in sub-Saharan Africa despite ongoing public health interventions. Our review highlights two important findings. First, the increasing resistance of malaria parasites to artemisinin-based combination therapy (ACT) and its partner drugs coupled with increased vector resistance to pyrethroids and insecticides is reversing the progress of public health interventions in keeping malaria under control. Second, the wanning for the efficacy of the WHO-approved vaccine i.e. RTS,S from 60 to 70% following 18 months of observation, and its short-term availability remains an impediment to achieving the WHO target of producing malaria vaccines with more than 75% efficacy by 2030. Our findings underline the need to reassess research priorities with a focus on vaccine production in sub-Saharan Africa. Furthermore, African governments and policymakers must be committed to invest both the political and financial capital in vaccine production and distribution.