Malaria research toward disease elimination

Studying malaria transmission biology using scRNA-sequencing provides information on within-host strain diversity and transcriptional states. Here, we comment on our collaborative efforts at establishing single-cell capacities in sub-Saharan Africa and the challenges encountered in Mali’s endemic setting.

Plasmodium malariae is a cause of malaria in humans and related species have been identified in non-human primates. Here, the authors use genomic analyses to establish that human P. malariae arose from a host switch of an ape parasite whilst a species infecting New World monkeys can be traced to a reverse zoonosis.

The function of RNA-binding domain abundant in Apicomplexans (RAP) protein family members is largely unknown. Here, using high-throughput functional genomics, including metabolomics, Hollin et al. characterize two RAP proteins that are essential for Plasmodium falciparum survival and control mitochondrial rRNAs.

Applying complexome profiling, Evers et al. unravel the composition of mitochondrial oxidative phosphorylation complexes in P. falciparum asexual and sexual blood stages. Abundance of these complexes differs between both stages, supporting the hypothesis that a mitochondrial metabolic switch is central to gametocyte development and functioning.

Here the authors use single-cell RNA-seq to profile the transmission stages of the human malaria parasite Plasmodium falciparum as it progresses through the Anopheles mosquito. They highlight unique patterns of gene usage throughout this development and identify potential pleiotropic genes that function at multiple life cycle stages.

After transmission of Plasmodium sporozoites from infected mosquitoes, parasites first infect hepatocytes. Here, Cha et al. identify a sporozoite ligand (phospholipid scramblase) and the hepatocytic receptor (carbamoyl-phosphate synthetase 1) as relevant for hepatocyte invasion and show that an antibody to hepatocyte-binding peptide 1 (HP1), which structurally mimics the sporozoite ligand, partially protects mice from infection.

During each replication cycle of P. falciparum in the human bloodstream, a small proportion of parasites commits to sexual development and differentiates into transmission-relevant gametocytes. Applying CRISPR-based genome editing, Boltryk et al. engineer P. falciparum lines with sexual commitment rates of 75% to promote future studies on gametocyte biology.

Here, Geoghegan, Evelyn et al. provide a lattice light-sheet microscopy based 4D imaging pipeline to quantitatively investigate Plasmodium spp. invasion and show that the nascent parasitophorous vacuole is predominantly formed from host’s erythrocyte membrane and undergoes continuous remodeling throughout invasion.

In placental malaria, interactions between parasite protein VAR2CSA and human glycosaminoglycan chondroitin sulfate A (CS) sequesters infected red blood cells in the placenta. Here, the authors provide cryo-EM structures of VAR2CSA and placental CS, identifying molecular interactions that could guide design of placental malaria vaccines.

Plasmodium falciparum moves by an atypical process called gliding motility which comprises of atypical myosin A (PfMyoA) and filaments of the dynamic and divergent PfActin-1 (PfAct1). Here authors present the cryo-EM structure of PfMyoA bound to filamentous PfAct1 stabilized with jasplakinolide and provide insights into the interactions that are required for the parasite to produce the force and motion required for infectivity.

Plasmodium falciparum secretes extracellular vesicles (EVs) while growing inside red blood cells (RBCs). Here the authors show that these EVs contain assembled and functional 20S proteasome complexes that remodel the cytoskeleton of naïve human RBCs, priming the RBCs for parasite invasion.

The chemokine CXCL10 is associated with pathogenesis of cerebral malaria in Plasmodium falciparum infection. Here the authors show that P. falciparum produces extracellular vesicles laden with RNAs that are taken up by monocytes resulting in a RIG-I and HUR-1 mediated mechanism of inhibition of CXCL10 protein translation.

RIFINs are Plasmodium surface antigens that suppress the immune response by binding inhibitory receptors such as LAIR1. Here, Xu et al. characterize the interaction between RIFIN-variable 2 domain and a LAIR1 domain and identify LAIR1-binding RIFINs in several Plasmodium species.

The transcription factor PfAP2-G is a key determinant of sexual commitment in Plasmodium falciparum. Here, Josling et al. define the transcriptional regulatory network of PfAP2-G by identifying its DNA binding sites genome-wide, which vary depending on the route of sexual conversion and rely on interactions with the PfAP2-I transcription factor.

While the role of Plasmodium EXP2 protein as translocon component of blood stage parasites is established, its functional role in liver stage parasites remains unclear. Here, Mello-Vieira et al. reveal that EXP2 pore-forming activity induces hepatocyte membrane repair and hence is critical for hepatocyte invasion.

Plasmodium protein phosphatase PP1 is essential for the asexual proliferation of malaria parasites. Here the authors show that PP1 regulates egress of parasites from host red blood cells, integrating parasite intrinsic pathways with environmental signals for release into the bloodstream.

The mechanism underlying periodicity of Plasmodium’s intra-erythrocytic developmental cycle (IDC) is unclear. Here, Subudhi et al. show that serpentine receptor 10 (SR10) plays a role in regulating the schedule of the IDC in line with the timing of host daily rhythms.

Mircobial symbionts of mosquitoes can affect transmission of human pathogens. Here, Herren et al. identify a microsporidian symbiont in Anopheles gambiae that impairs transmission without affecting mosquito fecundity or survival.

Rhoptries are essential organelles for invasion of erythrocytes by Plasmodium. Here, the authors characterize the rhoptry-associated protein CERLI1 using quantitative super-resolution microscopy, showing that it is important for parasite invasion and secretion of rhoptry proteins including vaccine antigens.

Here, Proto et al. show that human infective Plasmodium falciparum isolates contain an inactivating mutation in the erythrocyte invasion associated gene PfEBA165, while homologues of ape-infective Laverania species are intact, and that expression of intact PfEBA165 is incompatible with parasite growth in human erythrocytes.

Plasmodium growth is adapted to the reproductive cycle of mosquitoes, but underlying mechanisms are unclear. Here, Lampe et al. show that the blood-meal induced miR-276 balances the termination of the mosquito amino acid catabolism and egg development, providing nutrients for Plasmodium sporozoite development.

Here, the authors report transcriptomes and proteomes of oocyst sporozoite and salivary gland sporozoite stages in rodent-infectious Plasmodium yoelii parasites and human infectious Plasmodium falciparum parasites and define two waves of translational repression during sporozoite maturation.

Plasmodium vivax biology is not well understood, due to a lack of in vitro culture systems and difficulties associated with studying clinical blood samples. Here, Kim et al. use gene expression profiles from P. vivax infected patient blood and show stage-specific chloroquine response and differential regulation of male and female gametocytes.

Schizogony is essential for blood stage infection of Plasmodium parasites and produces several daughter cells. Here, Rudlaff et al. identify PfCINCH and interacting proteins as essential components of the basal complex required to establish daughter cell boundaries.

Here, Robert-Paganin et al. show that myosin A from Plasmodium falciparum is critical for red blood cell invasion and that non-canonical interactions and regulated phosphorylation are important for force generation during parasite invasion.

Malaria cases and deaths remain unacceptably high and are resurgent in several settings, though recent developments inspire optimism. This includes the approval of the world’s first malaria vaccine and results from novel vaccine candidates and trials testing innovative combinatorial interventions.

Release of genetically-modified sterile mosquitoes is a potential method of malaria control but has yet to be tested in the field. Here, the authors perform a mark-release-recapture experiment and show that genetically-modified mosquitoes have reduced survival and dispersal compared to wild-types.

In this phase 2 clinical trial, the authors assess protective efficacy of a Plasmodium vivax circumsporozoite vaccine in naïve and semi-immune individuals from controlled human malaria infection as well as antibody and IFN-γ response to vaccination.

Antibodies can have synergistic effects, but mechanisms are not well understood. Here, Ragotte et al. identify three antibodies that bind neighbouring epitopes on CyRPA, a malaria vaccine candidate, and show that lateral interactions between the antibodies slow dissociation and inhibit parasite growth synergistically.

In this placebo-controlled trial, 10/13 malaria naïve subjects immunized with a simplified regimen of chemoattenuated P. falciparum sporozoites, PfSPZ-CVac, show sterile protection from heterologous malaria challenge. Immunization was well tolerated and induced high levels of anti-PfCSP antibodies.

Control of mosquito populations using pesticides is important for malaria elimination, but effects of pesticides on humans aren’t well understood. Here, Prahl et al. show in a cohort of pregnant Ugandan women and their infants that household spraying with bendiocarb affects the fetal immune system and response to vaccination in infancy.

Here, Larsen et al. describe differences in Fc fucosylation of P. falciparum PfEMP1-specific IgG produced in response to natural infection versus VAR2CSA-type subunit vaccination, which leads to differences in the ability to induce FcγRIIIa-dependent natural killer cell degranulation.

Plasmodium vivax reticulocyte binding protein 2b (PvRBP2b) is important for invasion of reticulocytes and PvRBP2b antibodies correlate with protection. Here, Chan et al. isolate and characterize anti-PvRBP2b human monoclonal antibodies and describe mechanisms by which these antibodies inhibit invasion.

The most advanced P. falciparum circumsporozoite protein (PfCSP)-based malaria vaccine confers partial protection. Here, Pholcharee et al. present crystal structures, binding affinities/kinetics, and in vivo protection of 8 anti-NANP antibodies to understand in vivo protection of PfCSP-targeting antibodies.

Antibodies plays critical roles in the adaptive immune response to infectious agents including malaria. Here the authors defined antibody interactions with -Fcγ-receptors expressed on immune cells with sporozoites of Plasmodium falciparum, and identified specific target epitopes of antibodies.

Vaccines that interrupt malaria transmission will be important tools for malaria elimination. Here the authors identify a human monoclonal antibody from Pfs230 vaccinated individuals that blocks transmission of Plasmodium falciparum to mosquitoes in a complement-dependent manner and reacts with gamete surface.

Gene drives may be impeded by the generation of resistant alleles following NHEJ. Here the authors develop a recoded gene-drive rescue system for the malaria mosquito, Anopheles stephensi, that targets the drive to the kynurenine hydroxylase gene for negative selection against mutated alleles.

Here, the authors identify signatures of miRNA expression differentiation associated with Plasmodium falciparum infection and parasitemia in a longitudinal pediatric cohort in Burkina Faso. In particular, expression of several miRNAs known to promote lymphocyte cell death is affected during infection.

Duffy binding protein (DBP) of Plasmodium vivax is important for invasion and is a potential vaccine candidate. Here, the authors show that PvDBP gene amplification protects P vivax in vitro against invasion inhibitory human monoclonal antibodies and is associated to infection of patients with PvDBP binding inhibitory antibodies.

Inflammasome activation plays a role in malaria pathogenesis, but details aren’t well understood. Here, the authors show that caspase-8 is a central mediator of systemic inflammation in rodent malaria and that monocytes from malaria patients express active caspases-1, -4 and -8.

Proof of protection against blood-stage P. falciparum malaria by a single immunological mechanism has been elusive. Here, using engineered anti-PfRH5 chimeric monoclonal antibodies in non-human primates, the authors show that high levels of merozoite-neutralizing antibodies can achieve protection.

Bed nets treated with insecticides have been instrumental in reducing malaria mortality, but insecticide resistance is on the rise. Here, Mugenzi et al. identify genetic variants in the P450 gene CYP6P9b of Anopheles funestus that associate with insecticide resistance and develop a PCR-based diagnostic assay to help identify pyrethroid-resistant strains.

Relapse, reinfection and recrudescence can all cause recurrent infection after treatment of Plasmodium vivax malaria in endemic areas, but are difficult to distinguish. Here the authors show that they can be differentiated probabilistically and thereby demonstrate the high efficacy of primaquine treatment in preventing relapse.

Immune activation induces long-term alterations of setpoints, impacting responses to subsequent unrelated stimuli. Here the authors show that volunteers vaccinated with BCG respond to controlled human malaria infection with increased clinical symptoms and an inverse correlation between immune activation markers and parasitemia.

Pfs25 is a transmission-blocking vaccine candidate for Plasmodium. Here, McLeod et al. analyze the antibody response to Pfs25 in sera from a clinical trial evaluating a Pfs25 vaccine candidate, identify a potent transmission-blocking antibody and determine recognized epitopes on Pfs25.

Antibodies against Plasmodium falciparum merozoites that fix complement can inhibit blood-stage replication. Here, Reiling et al. show that complement-fixing antibodies strongly correlate with protective immunity in children, identify the merozoite targets, and predict antigen combinations that should result in strong protection.

Here, Minkah et al. show that, while immunization with replication-competent Plasmodium parasites can confer sterile protection against infection, it also induces a type I interferon response that adversely affects anti-malaria immunity by affecting numbers of protective hepatic CD8 T cells and CD8 T cell function.

RTS,S/AS01E has been tested in a phase 3 malaria vaccine trial and has shown partial efficacy in children and infants. Here, the authors analyze IgG concentration and avidity to CSP in ~1000 participants and show that IgG avidity to the C-terminus of CSP is significantly associated with vaccine-mediated protection.

So far identified clostridial neurotoxins target vertebrates. Here, Contreras et al. isolate the clostridial-like neurotoxin PMP1 from Paraclostridium bifermentans strains and show that it selectively targets anopheline mosquitoes by targeting mosquito syntaxin.

Host-parasite interactions during the exoerythrocytic stage of Plasmodium infection remains poorly understood. Using dual RNA-Seq, the authors show that human mucosal immunity protein mucin-13 is upregulated during Plasmodium hepatic-stage infection and marks infected cells independent of tested Plasmodium species.

Serological markers of recent Plasmodium falciparum infection could be useful to estimate incidence. Here, the authors identify a combination of five serological markers to detect exposure to infection within the previous three months with >80% sensitivity and specificity.

Here, de Vries et al. perform a pre-clinical characterization of the antimalarial compound MMV693183: the compound targets acetyl-CoA synthetase, has efficacy in humanized mice against Plasmodium falciparum infection, blocks transmission to mosquito vectors, is safe in rats, and pharmacokinetic-pharmacodynamic modeling informs about a potential oral human dosing regimen.

Repeating fever is a hallmark of malaria. Here, a large-scale forward genetic screen in malaria-causing Plasmodium falciparum identifies genes associated with parasite tolerance to host fever, including apicoplast targeted isoprenoid biosynthesis—sharing features with artemisinin resistance.

Here Arndt et al. establish rotating-crystal magneto-optical detection (RMOD) as a near-point-of-care diagnostic tool for malaria detection and report a sensitivity and specificity of 82% and 84%, respectively, as validated by analyzing a clinical population in a high transmission setting in Papua New Guinea.

The emergence and spread of artemisinin resistance has compromised antimalarial efficacy. Here, Mok et al. apply quantitative transcriptomics, proteomics, and metabolomics to provide evidence that K13 mutations alter multiple aspects of the parasite’s intra-erythrocytic development to enhance survival following artemisinin treatment.

Malaria gametocytes are sexual-stage parasites transmitted from mammalian host’s blood back to their insect vector. Here, Prajapati et al. identify gametocyte-committed ring-stage biomarkers allowing to forecast malaria transmission potential.

During Plasmodium intra-erythrocytic developmental, parasites compromise the structural integrity of host red-blood cells. Here, Clark et al. develop a flow cytometric osmotic stability assay to show that P. vivax infection destabilizes host reticulocytes, which are less stable than P. falciparum-infected normocytes.

Here, Reader et al. screen the Medicines for Malaria Venture Pandemic Response Box in parallel against Plasmodiumasexual and liver stage parasites, stage IV/V gametocytes, gametes, oocysts and as endectocides. They identify two potent transmission-blocking drugs: a histone demethylase inhibitor ML324 and the antitubercular SQ109.

Intermittent preventive treatment with dihydroartemisinin-piperaquine (DP) is protective in children against malaria. Here, the authors analyze plasma drug concentration, malaria incidence, and drug resistance markers from a clinical trial in Uganda and determine the optimal DP dosing regimen.

Bicyclic azetidine inhibitors are promising antimalarials that target the Plasmodium cytosolic phenylalanine tRNAsynthetase (cFRS). Here, Sharma et al. provide the biochemical and structural basis of its mechanism using co-crystal structure of PvcFRS with BRD1389.

Plasmodium falciparum infection in pregnancy is a major cause of adverse pregnancy outcomes. Here, the authors combine performance estimates of standard rapid diagnostic tests with modelling to assess whether screening at antenatal visits improves upon current intermittent preventative therapy.

The genome of the malaria parasite Plasmodium falciparum contains a record of past evolutionary forces. Here, using 2537 parasite sequences from the Democratic Republic of the Congo, the authors demonstrate how drug pressure and human movement have shaped the present-day parasite population.

Reliable plasmonic biosensors with high throughput and ease of use are highly sought after. Here, the authors report a plasmon-enhanced fluorescence antibody-aptamer biosensor based on a gold nanoparticle array, and demonstrate its use for effective specific detection of a malaria marker, at femtomolar level, in whole blood.

Plasmodium falciparum chloroquine resistance transporter (PfCRT) mediates multidrug resistance, but its natural function remains unclear. Here, Shafik et al. show that PfCRT transports host-derived peptides of 4-11 residues but not other ions or metabolites, and that drug-resistance-conferring PfCRT mutants have reduced peptide transport.

Imidazolopiperazines (IZPs) are a class of compounds under clinical development for malaria, but their mechanism of action is unclear. Here, the authors show that IZPs inhibit the parasite’s secretory pathway, affecting protein trafficking and export.

Plasmodium infection activates signaling pathways in a-nucleated erythrocytes. Here, Adderley et al. use a comprehensive antibody microarray to show that infection extensively modulates host cell signalling and that the host receptor tyrosine kinase c-MET supports Plasmodium falciparum proliferation.

Artemisinin (ART) resistance poses a problem for malaria elimination. Here, the authors perform genome-wide CRISPR screens in Toxoplasma gondii and identify that the putative transporter Tmem14c and mitochondrial heme metabolism, through mitochondrial protease DegP2, affect ART susceptibility.

Here, a cross of Plasmodium vivax malaria parasites links a chloroquine resistance (CQR) phenotype to a 76 kb region of chromosome 1 and greater expression of pvcrt, an ortholog of the Plasmodium falciparum CQR transporter gene.

Methods to diagnose malaria are of interest but can be costly or not sensitive enough to detect low levels of parasitemia. Here the authors report an ultrasensitive method by using hemozoin (a biomarker of all Plasmodium species) to catalyse the polymerization of N-isopropylacrylamide.

Here, the authors quantify early gametocyte-committed ring (gc-ring) stage Plasmodium falciparum parasites in 260 malaria patients 10 days before maturation to transmissible stage V gametocytes, and show that the ratio of circulating gc-rings is positively correlated with parasitemia and negatively correlated with body temperature.

The role of subpatent infections for malaria transmission and elimination is unclear. Here, Slater et al. analyse several malaria datasets to quantify the density, detectability, course of infection and infectiousness of subpatent infections.

Seasonal malaria chemoprevention provides substantial benefit for young children, but resistance to used drugs will likely develop. Here, Chotsiri et al. evaluate the use of dihydroartemisinin-piperaquine as a regimen in 179 children, and population-based simulations suggest that small children would benefit from a higher and extended dosage.

Primaquine (PQ) is a widely used anti-malaria drug, but its mechanism of action is unclear. Here, Camarda et al. show that PQ’s activity against liver and sexual Plasmodium stages depends on generation of hydroxylated-PQ metabolites (OH-PQm), which, undergoing further reactions, results in production of H₂O₂.

On the cusp of Plasmodium falciparum (Pf) elimination, Thailand is accelerating towards zero malaria by 2024. This commentary reviews the heart of its success—effective surveillance—and what else may be needed to reach zero on time.

Economic evaluations of public health interventions to prevent malaria should consider the adoption of wider perspectives and the inclusion of non-health impacts, particularly economic development outcomes, such as education. This is especially relevant in malaria elimination settings and in the context of the current SARS-CoV-2 pandemic.

Solar geoengineering, an emergency climate intervention, could shift one billion people back into areas of malaria risk. Regional tradeoffs and potential adverse outcomes point to the need for health sector planning with Global South leadership.

Climate conditions and urbanization can be major drivers of vector-borne infections. Here the authors demonstrate that an often-neglected climate variable, humidity, is an important factor for malaria epidemics in two urban areas in India.

Plasmodium vivax generally accounts for a low proportion of malaria cases in Africa, but population-level data on the distribution of infections is limited. Here, the authors use data from the Democratic Republic of the Congo and show that the prevalence is low (~3%) and diffusely spread.

Release of freshwater into the oceans as a result of ice sheet melting could impact the distribution of climate-sensitive diseases. Here, the authors show that a rapid ice sheet melting in Greenland could cause an emergence of malaria in Southern Africa whilst transmission risks in West Africa may decline.

In this longitudinal study of an incident (new infections) and chronic (asymptomatic infections) cohort of Plasmodium falciparum infection in children in Burkina Faso, the authors show higher gametocyte production and mosquito infectivity in chronic infections.

Malaria transmission-blocking vaccines are in development, but roll-out strategies have not been assessed. Here, the authors show that transmission-blocking activity is likely to be higher in the field than in laboratory conditions, and that school-aged children are an important group to target.

Asymptomatic malaria infections contribute to transmission. Here, Sumner et al. infer participant-to-mosquito transmission by sampling naturally-fed mosquitoes from households in Western Kenya and find that asymptomatic infections more than double the odds of transmission to a mosquito compared to symptomatic infections.

The genetic diversity of Plasmodium vivax strains in South Asia isn’t well described. Here, the authors sequence P. vivax from returning UK travelers and establish South Asian isolates as subpopulation distinct from East African and South East Asian isolates.

Indoor residual spraying (IRS) of insecticide is one of the primary malaria vector control initiatives, but implementation is limited. Here, the authors show that discontinuation of IRS in Uganda was associated with increased malaria incidence, and introduction of IRS was associated with decreased incidence.

Insecticide treated nets (ITNs) are an important part of malaria control in Africa and WHO targets aim for 80% coverage. This study estimates the spatio-temporal access and use of ITNs in Africa from 2000-2020, and shows that both metrics have improved over time but access remains below WHO targets.

Prior studies mapping climatologically suitable areas for malaria transmission have used relatively simple thresholds for precipitation. Here the authors show that when models incorporate hydrological processes a more complex pattern of malaria suitability emerges in Africa and future shifts in suitability are more pronounced.

Malaria prevalence in Papua New Guinea has risen in recent years after almost a decade of decline. In this study, the authors demonstrate that long-lasting insecticidal nets used in the country that were manufactured since 2013 have significantly reduced bioefficacy.

Four genome-wide associated loci are currently known for malaria susceptibility. Here, the authors expand on earlier work by combining data from 11 malaria-endemic countries and additional population sequencing informing an African-enriched imputation reference panel, with findings including a previously unreported association on chromosome 6.

Investigating malaria transmission at three sites in Uganda, the authors identify super-spreaders and show that super-spreading is more prominent at low-intensity transmission, and that seasonality and environmental stochasticity have a greater influence on super-spreading.

Understanding genomic variation in Plasmodium falciparum parasites and inferring migration patterns can guide malaria elimination strategies. Using genome-wide data for 1722 parasites collected from 54 districts, the authors use identity-by-descent approaches to estimate regional parasite migration and spread of artemisinin drug resistance.

Here, Nelson et al. use amplicon next-generation sequencing of two P. falciparum polymorphic gene regions to investigate the genetic similarity of parasite populations across time and space in a pediatric cohort in Kenya. They identify both micro- and macro-scale structuring of malaria parasites in this high-transmission setting, which could inform future intervention strategies.

Foreign aid is necessary to control tropical diseases in endemic countries. Here the authors outline the steps taken to control malaria in Africa since 2000 and present an economic model to propose that US$25−30 per capita will be needed to avoid a disease trap.