Influence of environmental, geographic, socio-demographic, and epidemiological factors on presence of malaria at the community level in two continents.

The interactions of environmental, geographic, socio-demographic, and epidemiological factors in shaping mosquito-borne disease transmission dynamics are complex and changeable, influencing the abundance and distribution of vectors and the pathogens they transmit. In this study, 27 years of cross-sectional malaria survey data (1990-2017) were used to examine the effects of these factors on Plasmodium falciparum and Plasmodium vivax malaria presence at the community level in Africa and Asia. Monthly long-term, open-source data for each factor were compiled and analyzed using generalized linear models and classification and regression trees. Both temperature and precipitation exhibited unimodal relationships with malaria, with a positive effect up to a point after which a negative effect was observed as temperature and precipitation increased. Overall decline in malaria from 2000 to 2012 was well captured by the models, as was the resurgence after that. The models also indicated higher malaria in regions with lower economic and development indicators. Malaria is driven by a combination of environmental, geographic, socioeconomic, and epidemiological factors, and in this study, we demonstrated two approaches to capturing this complexity of drivers within models. Identifying these key drivers, and describing their associations with malaria, provides key information to inform planning and prevention strategies and interventions to reduce malaria burden.

Preclinical development of a stabilized RH5 virus-like particle vaccine that induces improved antimalarial antibodies.

Plasmodium falciparum reticulocyte-binding protein homolog 5 (RH5) is a leading blood-stage malaria vaccine antigen target, currently in a phase 2b clinical trial as a full-length soluble protein/adjuvant vaccine candidate called RH5.1/Matrix-M. We identify that disordered regions of the full-length RH5 molecule induce non-growth inhibitory antibodies in human vaccinees and that a re-engineered and stabilized immunogen (including just the alpha-helical core of RH5) induces a qualitatively superior growth inhibitory antibody response in rats vaccinated with this protein formulated in Matrix-M adjuvant. In parallel, bioconjugation of this immunogen, termed "RH5.2," to hepatitis B surface antigen virus-like particles (VLPs) using the "plug-and-display" SpyTag-SpyCatcher platform technology also enables superior quantitative antibody immunogenicity over soluble protein/adjuvant in vaccinated mice and rats. These studies identify a blood-stage malaria vaccine candidate that may improve upon the current leading soluble protein vaccine candidate RH5.1/Matrix-M. The RH5.2-VLP/Matrix-M vaccine candidate is now under evaluation in phase 1a/b clinical trials.

Cimicifugin, a broad-spectrum inhibitor of Theileria annulata and Plasmodium falciparum CDK7.

Cyclin-dependent kinase 7 is an attractive therapeutic target for the treatment of cancers, and a previous report suggested that Plasmodium falciparum CDK7 is a potential drug target for developing new anti-malarial drugs. In this study, we aimed to characterize and evaluate the drug target potential of Theileria annulata CDK7. Theileria annulata is responsible for tropical theileriosis, which induces a phenotype similar to cancerous cells like immortalization, hyperproliferation, and dissemination. Virtual screening of the MyriaScreen II library predicted 14 compounds with high binding energies to the ATP-binding pocket of TaCDK7. Three compounds (cimicifugin, ST092793, and ST026925) of these 14 compounds were non-cytotoxic to the uninfected bovine cells (BoMac cells). Cimicifugin treatment led to the activation of the extrinsic apoptosis pathway and induced autophagy in T. annulata-infected cells. Furthermore, cimicifugin also inhibited the growth of P. falciparum, indicating that it has both anti-theilerial and anti-malarial activities and that TaCDK7 and PfCDK7 are promising drug targets.

From multisystem inflammatory syndrome in children to secondary hemophagocytic lymphohistiocytosis a series of misfortunate events: case report and review of literature.

Multisystem inflammatory syndrome of childhood (MIS-C) is a recently described entity in pediatrics post-COVID-19 pandemic. Hemophagocytic lymphohistiocytosis (HLH) is a clinical syndrome caused by an unregulated proliferation of macrophages as well as T lymphocytes. Both entities can be considered overlapping, although distinct criteria for each can be found in the literature. Herein, we report a patient with MIS-C post-COVID-19 infection, complicated with HLH secondary to Plasmodium falciparum malaria from a blood transfusion.

Linking Cerebral Malaria Pathogenesis to APOE-Mediated Amyloidosis: Observations and Hypothesis.

Although most children with cerebral malaria fully recover, more than a fifth of the survivors develop post-discharge neurodevelopmental sequelae suggestive of advanced neuronal injury. However, the cerebral molecular processes initiating neurological dysfunction in cerebral malaria are still debatable. In this article, we explore available data and hypothesise that cerebral malaria might be linked to APOE-mediated amyloidosis, one of the pathological processes associated with Alzheimer's disease. If our hypothesis is tested and found to be true, it could have far-reaching implications for what we know about cerebral malaria pathogenesis.

Genetic analysis of the circumsporozoite gene in Plasmodium falciparum isolates from Cameroon: Implications for efficacy and deployment of RTS,S/AS01 vaccine.

Current understanding of genetic polymorphisms and natural selection in Plasmodium falciparum circumsporozoite (PfCSP), the leading malaria vaccine, is crucial for the development of next-generation vaccines, and such data is lacking in Africa. Blood samples were collected among Plasmodium-infected individuals living in four Cameroonian areas (Douala, Maroua, Mayo-Oulo, Pette). DNA samples were amplified using nested PCR protocols, sequenced, and BLASTed. Single nucleotide polymorphisms (SNPs) were analysed in each PfCSP region, and their impact on PfCSP function/structure was predicted in silico. The N-terminal region showed a limited polymorphism with four haplotypes, and three novel SNPs (N68Y, R87W, K93E) were found. Thirty-five haplotypes were identified in the central region, with several variants (e.g., NVNP and KANP). The C-terminal region was also highly diverse, with 25 haplotypes and eight novel SNPs (N290D, N308I, S312G, K317A, V344I, D356E, E357L, D359Y). Most polymorphic codon sites were mainly observed in the Th2R subregion in isolates from Douala and Pette. The codon site 321 was under episodic positive selection. One novel (E357L) and three known (K322I, G349D, D359Y) SNPs show an impact on function/structure. This study showed extensive genetic diversity with geographical patterns and evidence of the selection of Cameroonian PfCSP central and C-terminal regions.

Relation between the Dantu blood group variant and bacteraemia in Kenyan children: a population-based case control study.

BACKGROUND: The Dantu blood group variant protects against P. falciparum infections but its wider consequences have not been previously explored. Here, we investigate the impact of Dantu on susceptibility to bacteraemia. METHODS: We conducted a case-control study in children presenting with community-acquired bacteraemia to Kilifi County Hospital in Kenya between 1998 and 2010. We used logistic regression to test for associations between the Dantu marker SNP rs186873296 A>G and both all-cause and pathogen-specific bacteraemia under an additive model. We used date of admission as a proxy measure of malaria transmission intensity, given known differences in malaria prevalence over the course of the study. RESULTS: Dantu was associated with protection from all-cause bacteraemia (OR=0.81, p=0.014), the association being greatest in homozygotes (OR=0.30, p=0.013). This protection was shared across the major bacterial pathogens but, notably, was only significant during the era of high malaria-transmission pre-2003 (OR=0.79, p=0.023). CONCLUSIONS: Consistent with previous studies showing the indirect impact on bacteraemia risk of other malaria-associated red cell variants, our study also shows that Dantu is protective against bacteraemia via its effect on malaria risk. Dantu does not appear to be under balancing selection through an increased risk of bacterial infections.

Repurposing of Drug Bank Compounds against Plasmodium falciparum Dihydroorotate Dehydrogenase as novel anti malarial drug candidates by Computational approaches.

This study aimed to repurpose Drug Bank Compounds against P. falciparum Dihydroorotate dehydrogenase (Pf-DHODH)a potential molecular target for antimalarial drug development due to its vital role in P. falciparum survival. Initially, the MATGEN server was used to screen drugs against Pf-DHODH (PDB ID 6GJG), followed by revalidating the results through docking by Autodock Vina through PyRx. Based on the docking results, three drugs namely, Talnifumate, Sulfaphenazole, and (3S)-N-[(2S)-1-[2-(1H-indol-3-yl)ethylamino]-1-oxopropan-2-yl]-1-(4-methoxyphenyl)-5-oxopyrrolidine-3-carboxamide-were subjected to molecular dynamics simulation for 100 ns. Molecular dynamics simulation results indicate that (3S)-N-[(2S)-1-[2-(1H-indol-3-yl)ethylamino]-1-oxopropan-2-yl]-1-(4-methoxyphenyl)-5-oxopyrrolidine-3-carboxamide- and Sulfaphenazole may target Pf-DHODH by forming a stable protein-ligand complex as they showed better free binding energy -130.58 kJ/mol, and -79.84 kJ/mol, respectively as compared to the free binding energy 116.255 kJ/mol of the reference compound; 3,6-dimethyl- ~ {N}-[4-(trifluoromethyl)phenyl]-[1,2]oxazolo[5,4-d]pyrimidin-4-amine. Although the studied compounds are drugs, still we applied Lipinski's rules and ADMET analysis that reconfirmed that these drugs have favorable drug-like properties. In conclusion, the results of the study show that Talniflumate and Sulfaphenazole may be potential antimalarial drug candidates.The derivatives of these drugs could be designed and tested to develop better drugs against Plasmodium species.

Malaria Tropica: An Autopsy Case Report With a Discussion on the Presence of Malaria in Bulgaria.

Malaria is an infectious disease caused by several types of parasitic plasmodia and transmitted to humans through Anopheles mosquitoes. The disease has long been widespread and has caused a significant number of deaths and decreased life quality from sequelae worldwide. As understanding of the disease increased immensely at the beginning of the 20th century, eradication plans were implemented to decrease disease transmission. This led to the successful eradication of malaria across predominantly industrialized countries, with multiple geographic areas remaining malaria endemic zones to this day. With climate changes and migration, the risk of reintroduction of malaria to malaria-free zones has risen due to relatively easy travel to endemic zones and importation of cases. On the one hand, this is a significant public health risk and, on the other, a challenge to the medical system, as healthcare workers in malaria-free zones are often ill-prepared to recognize, diagnose, and treat malaria cases. Herein, we present an autopsy and histopathology case report of tropical (falciparum) malaria, complicated with blackwater fever (malignant malaria) with prevalent gross and histopathological changes, including hemomelanin deposition in the spline, liver, and bone marrow; visible parasitic forms in the remaining red blood cells; Durk's granulomas, sludge, and petechial hemorrhages in the central nervous system; and hemoglobin casts within the renal tubular structures. We also discuss the history and risk of reintroducing malaria into a malaria-free zone - Bulgaria.

Cellular immune response to SARS-CoV-2 and clinical presentation in individuals exposed to endemic malaria.

Ghana and other parts of West Africa have experienced lower COVID-19 mortality rates than other regions. This phenomenon has been hypothesized to be associated with previous exposure to infections such as malaria. This study investigated the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the influence of previous malaria exposure. Blood samples were collected from individuals with asymptomatic or symptomatic COVID-19 (n = 217). A variety of assays were used to characterize the SARS-CoV-2-specific immune response, and malaria exposure was quantified using Plasmodium falciparum ELISA. The study found evidence of attenuated immune responses to COVID-19 among asymptomatic individuals, with elevated proportions of non-classical monocytes and greater memory B cell activation. Symptomatic patients displayed higher P. falciparum-specific T cell recall immune responses, whereas asymptomatic individuals demonstrated elevated P. falciparum antibody levels. Summarily, this study suggests that P. falciparum exposure-associated immune modulation may contribute to reduced severity of SARS-CoV-2 infection among people living in malaria-endemic regions.

Transcriptomic analyses of differentially expressed human genes, micro RNAs and long-non-coding RNAs in severe, symptomatic and asymptomatic malaria infection.

Malaria transmission and endemicity in Africa remains hugely disproportionate compared to the rest of the world. The complex life cycle of P. falciparum (Pf) between the vertebrate human host and the anopheline vector results in differential expression of genes within and between hosts. An in-depth understanding of Pf interaction with various human genes through regulatory elements will pave way for identification of newer tools in the arsenal for malaria control. Therefore, the regulatory elements (REs) involved in the over- or under-expression of various host immune genes hold the key to elucidating alternative control measures that can be applied for disease surveillance, prompt diagnosis and treatment. We carried out an RNAseq analysis to identify differentially expressed genes and network elucidation of non-coding RNAs and target genes associated with immune response in individuals with different clinical outcomes. Raw RNAseq datasets, retrieved for analyses include individuals with severe (Gambia-20), symptomatic (Burkina Faso-15), asymptomatic (Mali-16) malaria as well as uninfected controls (Tanzania-20; Mali-36). Of the total 107 datasets retrieved, we identified 5534 differentially expressed genes (DEGs) among disease and control groups. A peculiar pattern of DEGs was observed, with individuals presenting with severe/symptomatic malaria having the highest and most diverse upregulated genes, while a reverse phenomenon was recorded among asymptomatic and uninfected individuals. In addition, we identified 141 differentially expressed micro RNA (miRNA), of which 78 and 63 were upregulated and downregulated respectively. Interactome analysis revealed a moderate interaction between DEGs and miRNAs. Of all identified miRNA, five were unique (hsa-mir-32, hsa-mir-25, hsa-mir-221, hsa-mir-29 and hsa-mir-148) because of their connectivity to several genes, including hsa-mir-221 connected to 16 genes. Six-hundred and eight differentially expressed long non coding RNA (lncRNA) were also identified, including SLC7A11, LINC01524 among the upregulated ones. Our study provides important insight into host immune genes undergoing differential expression under different malaria conditions. It also identified unique miRNAs and lncRNAs that modify and/or regulate the expression of various immune genes. These regulatory elements we surmise, have the potential to serve a diagnostic purpose in discriminating between individuals with severe/symptomatic malaria and those with asymptomatic infection or uninfected, following further clinical validation from field isolates.

Chemoproteomics validates selective targeting of Plasmodium M1 alanyl aminopeptidase as an antimalarial strategy.

New antimalarial drug candidates that act via novel mechanisms are urgently needed to combat malaria drug resistance. Here, we describe the multi-omic chemical validation of Plasmodium M1 alanyl metalloaminopeptidase as an attractive drug target using the selective inhibitor, MIPS2673. MIPS2673 demonstrated potent inhibition of recombinant Plasmodium falciparum (PfA-M1) and Plasmodium vivax (PvA-M1) M1 metalloaminopeptidases, with selectivity over other Plasmodium and human aminopeptidases, and displayed excellent in vitro antimalarial activity with no significant host cytotoxicity. Orthogonal label-free chemoproteomic methods based on thermal stability and limited proteolysis of whole parasite lysates revealed that MIPS2673 solely targets PfA-M1 in parasites, with limited proteolysis also enabling estimation of the binding site on PfA-M1 to within ~5 Å of that determined by X-ray crystallography. Finally, functional investigation by untargeted metabolomics demonstrated that MIPS2673 inhibits the key role of PfA-M1 in haemoglobin digestion. Combined, our unbiased multi-omic target deconvolution methods confirmed the on-target activity of MIPS2673, and validated selective inhibition of M1 alanyl metalloaminopeptidase as a promising antimalarial strategy.

The effect of single low-dose primaquine treatment for uncomplicated Plasmodium falciparum malaria on haemoglobin levels in Ethiopia: a longitudinal cohort study.

BACKGROUND: To interrupt residual malaria transmission and achieve successful elimination of Plasmodium falciparum in low-transmission settings, the World Health Organization (WHO) recommends the administration of a single dose of 0.25 mg/kg (or 15 mg/kg for adults) primaquine (PQ) combined with artemisinin-based combination therapy (ACT), without glucose-6-phosphate dehydrogenase (G6PD) testing. However, due to the risk of haemolysis in patients with G6PD deficiency (G6PDd), PQ use is uncommon. Thus, this study aimed to assess the safety of a single low dose of PQ administered to patients with G6PD deficiency. METHODS: An observational cohort study was conducted with patients treated for uncomplicated P. falciparum malaria with either single-dose PQ (0.25 mg/kg) (SLD PQ) + ACT or ACT alone. Microscopy-confirmed uncomplicated P. falciparum malaria patients visiting public health facilities in Arjo Didessa, Southwest Ethiopia, were enrolled in the study from September 2019 to November 2022. Patients with uncomplicated P. falciparum malaria were followed up for 28 days through clinical and laboratory diagnosis, such as measurements of G6PD levels and haemoglobin (Hb) concentrations. G6PD levels were measured by a quantiative CareSTART™ POCT S1 biosensor machine. Patient interviews were also conducted, and the type and frequency of clinical complaints were recorded. Hb data were taken on days (D) 7, 14, 21, and 28 following treatment with SLD-PQ + ACT or ACT alone. RESULTS: A total of 249 patients with uncomplicated P. falciparum malaria were enrolled in this study. Of these, 83 (33.3%) patients received ACT alone, and 166 (66.7%) received ACT combined with SLD-PQ treatment. The median age of the patients was 20 (IQR 28-15) years. G6PD deficiency was found in 17 (6.8%) patients, 14 males and 3 females. There were 6 (7.2%) and 11 (6.6%) phenotypic G6PD-deficient patients in the ACT alone and ACT + SLD-PQ arms, respectively. The mean Hb levels in patients treated with ACT + SLD-PQ were reduced by an average of 0.45 g/dl (95% CI = 0.39 to 0.52) in the posttreatment phase (D7) compared to a reduction of 0.30 g/dl (95% CI = 0.14 to - 0.47) in patients treated with ACT alone (P = 0.157). A greater mean Hb reduction was observed on day 7 in the G6PDd ACT + SLD-PQ group (- 0.60 g/dL) than in the G6PDd ACT alone group (- 0.48 g/dL); however, there was no statistically significant difference (P = 0.465). Overall, D14 losses were 0.10 g/dl (95% CI = - 0.00 to 0.20) and 0.05 g/dl (95% CI = - 0.123 to 0.22) in patients with and without SLD-PQ, respectively (P = 0.412). CONCLUSIONS: This study's findings indicate that using SLD-PQ in combination with ACT is safe for uncomplicated P. falciparum malaria regardless of the patient's G6PD status in Ethiopian settings. Caution should be taken in extrapolating this finding in other settings with diverse G6DP phenotypes.

Evaluation of combination vaccines targeting transmission of Plasmodium falciparum and P. vivax.

Transmission-blocking vaccines interrupting malaria transmission within mosquitoes represent an ideal public health tool to eliminate malaria at the population level. Plasmodium falciparum and P. vivax account for more than 90% of the global malaria burden, co-endemic in many regions of the world. P25 and P48/45 are two leading candidates for both species and have shown promising transmission-blocking activity in preclinical and clinical studies. However, neither of these target antigens as individual vaccines has induced complete transmission inhibition in mosquitoes. In this study, we assessed immunogenicity of combination vaccines based on P25 and P48/45 using a DNA vaccine platform to broaden vaccine specificity against P. falciparum and P. vivax. Individual DNA vaccines encoding Pvs25, Pfs25, Pvs48/45 and Pfs48/45, as well as various combinations including (Pvs25 + Pvs48/45), (Pfs25 + Pfs48/45), (Pvs25 + Pfs25), and (Pvs48/45 + Pfs48/45), were evaluated in mice using in vivo electroporation. Potent antibody responses were induced in mice immunized with individual and combination DNA vaccines, and specific antibody responses were not compromised when combinations of DNA vaccines were evaluated against individual DNA vaccines. The anti-Pvs25 IgG from individual and combination groups revealed concentration-dependent transmission-reducing activity (TRA) in direct membrane feeding assays (DMFA) using blood from P. vivax-infected donors in Brazil and independently in ex vivo MFA using Pvs25-transgenic P. berghei. Similarly, anti-Pfs25 and anti-Pfs48/45 IgGs from mice immunized with Pfs25 and Pfs48/45 DNA vaccines individually and in various combinations revealed antibody dose-dependent TRA in standard membrane feeding assays (SMFA) using culture-derived P. falciparum gametocytes. However, antibodies induced by immunization with Pvs48/45 DNA vaccines were ineffective in DMFA and require further vaccine construct optimization, considering the possibility of induction of both transmission-blocking and transmission-enhancing antibodies revealed by competition ELISA. These studies provide a rationale for combining multiple antigens to simultaneously target transmission of malaria caused by P. falciparum and P. vivax.

Dose-dependent inactivation of Plasmodium falciparum in red blood cell concentrates by treatment with short-wavelength ultraviolet light.

BACKGROUND AND OBJECTIVES: Plasmodium species are naturally transmitted by Anopheles mosquitos. The parasite infects red blood cells (RBCs) and can be transfused with blood products. In non-endemic areas, the main risk of infection arises from travellers coming back and people immigrating from malaria-endemic regions. Endemic countries face a permanent risk of infection from transfusion-transmitted malaria (TTM). TTM may cause life-threatening complications in patients dependent on blood donations. This study aimed to investigate the efficacy of Plasmodium falciparum inactivation in RBC units by treatment with short-wavelength ultraviolet C (UVC) light in the absence of photochemical additives. MATERIALS AND METHODS: RBC units were spiked with P. falciparum to a parasite density of 0.1%-1% and irradiated with up to 4.5 J/cm2 UVC. The parasite density of UVC-treated dilution series and untreated controls were compared over 3 weeks after irradiation. RESULTS: The lowest dose of 1.5 J/cm2 UVC led to a 3.1 log reduction in parasite load compared with the untreated control. The inactivation capacity was dose-dependent. Strikingly, 4.5 J/cm2 led to ≥5.3 log unit reduction, which was equivalent to a complete inactivation in two out of three experiments. CONCLUSION: Pathogen reduction with UVC light was previously shown to be effective for different bacteria and viruses, but the inactivation of parasites in RBC concentrates was not addressed until now. The present study provides evidence for significant inactivation of P. falciparum-infected RBCs by UVC light.

High Frequency of Deletions in the pfhrp2 and pfhrp3 Genes of Plasmodium falciparum in the Middle Rio Negro Region of the Brazilian Amazon.

Several countries are reporting natural populations of P. falciparum with deletions in the pfhrp2/3 genes that can lead to false-negative results in rapid diagnostic tests. To investigate the prevalence of deletion in the pfhrp2/3 genes in the Rio Negro basin in the Brazilian Amazon and identify whether there is clinical differentiation between individuals infected by these parasites, clinical samples collected from 2003 to 2016 were analyzed from symptomatic and asymptomatic P. falciparum-infected individuals. The molecular deletion of pfhrp2 and pfhrp3 genes was evaluated using the protocols recommended by the WHO. From 82 samples used, 28 (34.2%) had a single deletion in pfhrp2, 19 (23.2%) had a single deletion in pfhrp3, 15 (18.3%) had a double deletion (pfhrp2/3), and 20 (24.4%) did not have a deletion in either gene. In total, 29.3% of individuals had an asymptomatic plasmodial infection and were 3.64 times more likely to have parasites with a double deletion (pfhrp2/3) than patients with clinical malaria (p = 0.02). The high prevalence of parasites with pfhrp2/3 deletions shows the need to implement a surveillance program in this area. Deletions in parasites may be associated with the clinical pattern of the disease in this area. More studies must be carried out to elucidate these findings.

Antiplasmodial potential of isolated xanthones from Mesua ferrea Linn. roots: an in vitro and in silico molecular docking and pharmacokinetics study.

BACKGROUND: Malaria is a major global health concern, particularly in tropical and subtropical countries. With growing resistance to first-line treatment with artemisinin, there is an urgent need to discover novel antimalarial drugs. Mesua ferrea Linn., a plant used in traditional medicine for various purposes, has previously been investigated by our research group for its cytotoxic properties. The objective of this study was to explore the compounds isolated from M. ferrea with regards to their potential antiplasmodial activity, their interaction with Plasmodium falciparum lactate dehydrogenase (PfLDH), a crucial enzyme for parasite survival, and their pharmacokinetic and toxicity profiles. METHODS: The isolated compounds were assessed for in vitro antiplasmodial activity against a multidrug-resistant strain of P. falciparum K1 using a parasite lactate dehydrogenase (pLDH) assay. In vitro cytotoxicity against Vero cells was determined using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The interactions between the isolated compounds and the target enzyme PfLDH were investigated using molecular docking. Additionally, pharmacokinetic and toxicity properties were estimated using online web tools SwissADME and ProTox-II, respectively. RESULTS: Among the seven compounds isolated from M. ferrea roots, rheediachromenoxanthone (5), which belongs to the pyranoxanthone class, demonstrated good in vitro antiplasmodial activity, with the IC50 being 19.93 µM. Additionally, there was no toxicity towards Vero cells (CC50 = 112.34 µM) and a selectivity index (SI) of 5.64. Molecular docking analysis revealed that compound (5) exhibited a strong binding affinity of - 8.6 kcal/mol towards PfLDH and was stabilized by forming hydrogen bonds with key amino acid residues, including ASP53, TYR85, and GLU122. Pharmacokinetic predictions indicated that compound (5) possessed favorable drug-like properties and desired pharmacokinetic characteristics. These include high absorption in the gastrointestinal tract, classification as a non-substrate of permeability glycoprotein (P-gp), non-inhibition of CYP2C19, ease of synthesis, a high predicted LD50 value of 4,000 mg/kg, and importantly, non-hepatotoxic, non-carcinogenic, and non-cytotoxic effects. CONCLUSIONS: This study demonstrated that compounds isolated from M. ferrea exhibit activity against P. falciparum. Rheediachromenoxanthone has significant potential as a scaffold for the development of potent antimalarial drugs.

The malaria parasite egress protease SUB1 is activated through precise, plasmepsin X-mediated cleavage of the SUB1 prodomain.

BACKGROUND: The malaria parasite Plasmodium falciparum replicates within red blood cells, then ruptures the cell in a process called egress in order to continue its life cycle. Egress is regulated by a proteolytic cascade involving an essential parasite subtilisin-like serine protease called SUB1. Maturation of SUB1 initiates in the parasite endoplasmic reticulum with autocatalytic cleavage of an N-terminal prodomain (p31), which initially remains non-covalently bound to the catalytic domain, p54. Further trafficking of the p31-p54 complex results in formation of a terminal p47 form of the SUB1 catalytic domain. Recent work has implicated a parasite aspartic protease, plasmepsin X (PMX), in maturation of the SUB1 p31-p54 complex through controlled cleavage of the prodomain p31. METHODS: Here we use biochemical and enzymatic analysis to examine the activation of SUB1 by PMX. RESULTS: We show that both p31 and p31-p54 are largely dimeric under the relatively acidic conditions to which they are likely exposed to PMX in the parasite. We confirm the sites within p31 that are cleaved by PMX and determine the order of cleavage. We find that cleavage by PMX results in rapid loss of the capacity of p31 to act as an inhibitor of SUB1 catalytic activity and we directly demonstrate that exposure to PMX of recombinant p31-p54 complex activates SUB1 activity. CONCLUSIONS: Our results confirm that precise, PMX-mediated cleavage of the SUB1 prodomain activates SUB1 enzyme activity. GENERAL SIGNIFICANCE: Our findings elucidate the role of PMX in activation of SUB1, a key effector of malaria parasite egress.

Impact on pregnancy outcomes of intermittent preventive treatment with sulfadoxine-pyrimethamine in urban and peri-urban Papua New Guinea: a retrospective cohort study.

BACKGROUND: Intermittent preventive treatment in pregnancy with sulfadoxine-pyrimethamine (IPTp-SP) reduces malaria-attributable adverse pregnancy outcomes and may also prevent low birth weight (< 2,500 g) through mechanisms independent of malaria. Malaria transmission in Papua New Guinea (PNG) is highly heterogeneous. The impact of IPTp-SP on adverse birth outcomes in settings with little or no malaria transmission, such as PNG's capital city Port Moresby, is unknown. METHODS: A retrospective cohort study was conducted amongst HIV-negative women with a singleton pregnancy who delivered at Port Moresby General Hospital between 18 July and 21 August 2022. The impact of IPTp-SP doses on adverse birth outcomes and anaemia was assessed using logistic and linear regression models, as appropriate. RESULTS: Of 1,140 eligible women amongst 1,228 consecutive births, 1,110 had a live birth with a documented birth weight. A total of 156 women (13.7%) did not receive any IPTp-SP, 347 women (30.4%) received one, 333 (29.2%) received two, and 304 (26.7%) received the recommended ≥ 3 doses of IPTp-SP. A total of 65 of 1,110 liveborn babies (5.9%) had low birth weight and there were 34 perinatal deaths (3.0%). Anaemia (haemoglobin < 100 g/L) was observed in 30.6% (243/793) of women, and 14 (1.2%) had clinical malaria in pregnancy. Compared to women receiving 0-1 dose of IPTp-SP, women receiving ≥ 2 doses had lower odds of LBW (adjusted odds ratio [aOR] 0.50; 95% confidence interval [CI] 0.26, 0.96), preterm birth (aOR 0.58; 95% CI 0.32, 1.04), perinatal death (aOR 0.49; 95% CI 0.18, 1.38), LBW/perinatal death (aOR 0.55; 95% CI 0.27, 1.12), and anaemia (OR 0.50; 95% CI 0.36, 0.69). Women who received 2 doses versus 0-1 had 45% lower odds of LBW (aOR 0.55, 95% CI 0.27, 1.10), and a 16% further (total 61%) reduction with ≥ 3 doses (aOR 0.39, 95% CI 0.14, 1.05). Birth weights for women who received 2 or ≥ 3 doses versus 0-1 were 81 g (95% CI -3, 166) higher, and 151 g (58, 246) higher, respectively. CONCLUSIONS: Provision of IPTp-SP in a low malaria-transmission setting in PNG appears to translate into substantial health benefits, in a dose-response manner, supporting the strengthening IPTp-SP uptake across all transmission settings in PNG.

Infectivity of Plasmodium parasites to Aedes aegypti and Anopheles stephensi mosquitoes maintained on blood-free meals of SkitoSnack.

BACKGROUND: Aedes and Anopheles mosquitoes are responsible for tremendous global health burdens from their transmission of pathogens causing malaria, lymphatic filariasis, dengue, and yellow fever. Innovative vector control strategies will help to reduce the prevalence of these diseases. Mass rearing of mosquitoes for research and support of these strategies presently depends on meals of vertebrate blood, which is subject to acquisition, handling, and storage issues. Various blood-free replacements have been formulated for these mosquitoes, but none of these replacements are in wide use, and little is known about their potential impact on competence of the mosquitoes for Plasmodium infection. METHODS: Colonies of Aedes aegypti and Anopheles stephensi were continuously maintained on a blood-free replacement (SkitoSnack; SS) or bovine blood (BB) and monitored for engorgement and hatch rates. Infections of Ae. aegypti and An. stephensi were assessed with Plasmodium gallinaceum and P. falciparum, respectively. RESULTS: Replicate colonies of mosquitoes were maintained on BB or SS for 10 generations of Ae. aegypti and more than 63 generations of An. stephensi. The odds of engorgement by SS- relative to BB-maintained mosquitoes were higher for both Ae. aegypti (OR = 2.6, 95% CI 1.3-5.2) and An. stephensi (OR 2.7, 95% CI 1.4-5.5), while lower odds of hatching were found for eggs from the SS-maintained mosquitoes of both species (Ae. aegypti OR = 0.40, 95% CI 0.26-0.62; An. stephensi OR = 0.59, 95% CI 0.36-0.96). Oocyst counts were similar for P. gallinaceum infections of Ae. aegypti mosquitoes maintained on SS or BB (mean ratio = [mean on SS]/[mean on BB] = 1.11, 95% CI 0.85-1.49). Similar oocyst counts were also observed from the P. falciparum infections of SS- or BB-maintained An. stephensi (mean ratio = 0.76, 95% CI 0.44-1.37). The average counts of sporozoites/mosquito showed no evidence of reductions in the SS-maintained relative to BB-maintained mosquitoes of both species. CONCLUSIONS: Aedes aegypti and An. stephensi can be reliably maintained on SS over multiple generations and are as competent for Plasmodium infection as mosquitoes maintained on BB. Use of SS alleviates the need to acquire and preserve blood for mosquito husbandry and may support new initiatives in fundamental and applied research, including novel manipulations of midgut microbiota and factors important to the mosquito life cycle and pathogen susceptibility.