Genetic diversity of glutamate-rich protein (GLURP) in Plasmodium falciparum isolates from school-age children in Kinshasa, DRC

Malaria infections in school-age children further make it difficult to control the disease's spread. Moreover, the genetic diversity of glutamate-rich protein, potentially a candidate for vaccine development, has not yet been investigated in the Democratic Republic of Congo. Therefore, we aimed to assess the genetic diversity of the immunodominant C-terminal repetitive region (R2) of Plasmodium falciparum glutamate-rich protein gene (pfglurp) among school-age children living in Kinshasa, DRC. We conducted nested PCR targeting R2 of pfglurp and the amplicon were directly sequenced. We summarized the prevalence of mutations of bases and amino acids and indicated the amino acid repeat sequence in the R2 region by the unit code. We then statistically analyzed whether there was a relationship between the number of mutations in the pfglurp gene and attributes. In 221 samples, haplotype 1 was the most common (n = 137, 61.99%), with the same sequence as the 3D7 strain. Regarding the number of base mutations, it was higher in urban areas than rural areas (p = 0.0363). When genetic neutrality was tested using data from 171 samples of the single strain, Tajima's D was -1.857 (p = 0.0059). In addition, FST as the genetic distance between all attributes was very small and no significant difference was observed. This study clarified the genetic mutation status and relevant patient attributes among School-age children in the DRC. We found that urban areas are more likely to harbour pfglurp mutations. Future research needs to clarify the reason and mechanism involved.

Skeleton binding protein 1 localizes to the Maurer's cleft and interacts with PfHSP70-1 and PfHSP70-x in Plasmodium falciparum gametocyte-infected erythrocytes

Plasmodium falciparum accounts for the majority of malaria deaths, due to pathology provoked by the ability of infected erythrocytes to adhere to vascular endothelium within deep tissues. The parasite recognizes endothelium by trafficking and displaying protein ligands on the surface of asexual stage infected erythrocytes, such as members of the large family of pathogenic proteins, P. falciparum erythrocyte membrane protein 1 (PfEMP1). Parasite-encoded skeleton binding protein 1 (SBP1) plays an important role in the transport of these binding-related surface proteins, via cleft-like membranous structures termed Maurer's clefts, which are present within the cytoplasm of infected erythrocytes. Erythrocytes infected with gametocyte stages accumulate in the extravascular compartment of bone marrow; and it was suggested that their surface-expressed adhesion molecule profile and protein trafficking mechanisms might differ from those in asexual stage parasites. Protein trafficking mechanisms via Maurer's clefts have been well investigated in asexual stage parasite-infected erythrocytes; but little is known regarding the gametocyte stages. In this study, we characterized SBP1 during gametocyte maturation and demonstrated that SBP1 is expressed and localizes to dot-like Maurer's cleft structures in the cytoplasm of gametocyte-infected erythrocytes. Co-immunoprecipitation and mass spectrometry assays indicated that SBP1 interacts with the molecular chaperones PfHSP70-1 and PfHSP70-x. Localization analysis suggested that some PfHSP70-1 and/or PfHSP70-x localize in a dot-like pattern within the cytoplasm of immature gametocyte-infected erythrocytes. These findings suggest that SBP1 may interact with HSP70 chaperones in the infected erythrocyte cytoplasm during the immature gametocyte stages.

Design, synthesis and Anti-Plasmodial activity of Mortiamide-Lugdunin conjugates

In this study, two linear and corresponding cyclic heptapeptide versions of mortiamide A-lugdunin hybrids were designed and synthesized by integrating an anti-malarial peptide epitope derived from Mortiamide A, combined with four residues known for their membrane interactions. Using this synthetic strategy, the sequence of mortiamide A was partly re-engineered with an epitope sequence of lugdunin along with an amino acid replacement using all-L and D/L configurations. Importantly, the re-engineered cyclic mortiamides with all-L (3) and D/L (4) configurations exhibited promising anti-malarial activities against the P. falciparum drug-sensitive TM4/8 strain with half-maximal inhibitory concentration (IC50) values of 6.2 ± 0.5 and 4.8 ± 0.1 μM, respectively. Additionally, they exhibited anti-malarial activities against the P. falciparum multidrug-resistant V1/S strain with IC50 values of 5.0 ± 2.6 and 3.7 ± 0.7 μM, respectively. Interestingly, a linear re-engineered mortiamide with D/L configuration (2) exhibited promising anti-malarial activities, surpassing those of the re-engineered cyclic mortiamides (3 and 4), against both the P. falciparum sensitive TM4/8 and multidrug-resistant V1/S strains with IC50 values of 3.6 ± 0.5 and 2.8 ± 0.7 μM (IC50 of Mortiamide A = 7.85 ± 0.97, 5.31 ± 0.24 μM against 3D7 and Dd2 strains) without any cytotoxicity at >100 µM. The presence of D/L forms in a linear structure significantly impacted the anti-malarial activity against both the P. falciparum sensitive TM4/8 strain and the multidrug-resistant V1/S strain.

Synthesis and biological evaluation of hydantoin derivatives as potent antiplasmodial agents

Malaria, a devastating disease, has claimed numerous lives and caused considerable suffering, with young children and pregnant women being the most severely affected group. However, the emergence of multidrug-resistant strains of Plasmodium and the adverse side effects associated with existing antimalarial drugs underscore the urgent need for the development of novel, well-tolerated, and more efficient drugs to combat this global health threat. To address these challenges, six new hydantoins derivatives were synthesized and evaluated for their in vitro antiplasmodial activity. Notably, compound 2c exhibited excellent inhibitory activity against the tested Pf3D7 strain, with an IC50 value of 3.97 ± 0.01 nM, three-fold better than chloroquine. Following closely, compound 3b demonstrated an IC50 value of 27.52 ± 3.37 µM against the Pf3D7 strain in vitro. Additionally, all the hydantoins derivatives tested showed inactive against human MCR-5 cells, with an IC50 value exceeding 100 μM. In summary, the hydantoin derivative 2c emerges as a promising candidate for further exploration as an antiplasmodial compound.

mSphere of Influence: Deciphering purine auxotrophy in protozoan parasites

Bruno Martorelli Di Genova works in parasitology, focusing on Toxoplasma gondii metabolism. In this mSphere of Influence article, he reflects on how the articles "Metabolic Reprogramming during Purine Stress in the Protozoan Pathogen Leishmania donovani" and "Yeast-Based High-Throughput Screen Identifies Plasmodium falciparum Equilibrative Nucleoside Transporter 1 Inhibitors That Kill Malaria Parasites" impacted him, informing his research strategies and understanding of metabolic flexibility in Toxoplasma gondii.

Novel hydrazone compounds with broad-spectrum antiplasmodial activity and synergistic interactions with antimalarial drugs

The development of novel antiplasmodial compounds with broad-spectrum activity against different stages of Plasmodium parasites is crucial to prevent malaria disease and parasite transmission. This study evaluated the antiplasmodial activity of seven novel hydrazone compounds (referred to as CB compounds: CB-27, CB-41, CB-50, CB-53, CB-58, CB-59, and CB-61) against multiple stages of Plasmodium parasites. All CB compounds inhibited blood stage proliferation of drug-resistant or sensitive strains of Plasmodium falciparum in the low micromolar to nanomolar range. Interestingly, CB-41 exhibited prophylactic activity against hypnozoites and liver schizonts in Plasmodium cynomolgi, a primate model for Plasmodium vivax. Four CB compounds (CB-27, CB-41, CB-53, and CB-61) inhibited P. falciparum oocyst formation in mosquitoes, and five CB compounds (CB-27, CB-41, CB-53, CB-58, and CB-61) hindered the in vitro development of Plasmodium berghei ookinetes. The CB compounds did not inhibit the activation of P. berghei female and male gametocytes in vitro. Isobologram assays demonstrated synergistic interactions between CB-61 and the FDA-approved antimalarial drugs, clindamycin and halofantrine. Testing of six CB compounds showed no inhibition of Plasmodium glutathione S-transferase as a putative target and no cytotoxicity in HepG2 liver cells. CB compounds are promising candidates for further development as antimalarial drugs against multidrug-resistant parasites, which could also prevent malaria transmission.

Characterization of drug resistance genes in Indian Plasmodium falciparum and Plasmodium vivax field isolates

One of the major challenges for malaria control and elimination is the spread and emergence of antimalarial drug resistance. Mutations in Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) field isolates for five drug resistance genes viz. crt, mdr1, dhps, dhfr and kelch known to confer resistance to choloroquine (CQ), sulfadoxine-pyrimethamine (SP) and artemisinin (ART) and its derivatives were analyzed. A total of 342 symptomatic isolates of P. falciparum (Pf) and P. vivax (Pv) from 1993 to 2014 were retrieved from malaria parasite repository at National Institute of Malaria Research (NIMR). Sample DNA was extracted from dried blood spots and various targeted single nucleotide polymorphisms (SNPs) associated with antimalarial drug resistance were analysed for these isolates. C72S (67.7%) and K76T (83.8%) mutations along with SVMNT haplotype (67.7%) predominated the study population for Pfcrt. The most prevalent SNPs were S108N (73.2%) and A437G (24.8%) and the most prevalent haplotypes were ACNRNI (51.9%) and SAKAA (74.5%) in Pfdhfr and Pfdhps respectively. Only two mutations in Pfmdr1, N86Y (26.31%) and Y184F (56.26%), were seen frequently in our study population. No mutations associated with Pfk13 were observed. For Pv, all the studied isolates showed two Pvdhps mutations, A383G and A553G, and two Pfdhfr mutations, S58R and S117N. Similarly, three mutations, viz. T958M, M908L and F1076L were found in Pvmdr1. No variations were observed in Pvcrt-o and Pvk12 genes. Overall, our study demonstrates an increase in mutations associated with SP resistance in both Pf and Pv, however, no single nucleotide polymorphisms (SNPs) associated with ART resistance have been observed for either species. Various SNPs associated with CQ resistance were seen in Pf; whereas only Pvmdr1 associated resistant SNPs were observed in Pv. Therefore, molecular characterization of drug resistance genes is essential for timely monitoring and prevention of malaria by identifying the circulating drug resistant parasites in the country.

Comparison of prevalence estimates of pfhrp2 and pfhrp3 deletions in Plasmodium falciparum determined by conventional PCR and multiplex qPCR and implications for surveillance and monitoring

OBJECTIVES

Accuracy of malaria rapid diagnostic tests is threatened by Plasmodium falciparum with pfhrp2/3 deletions. This study compares gene deletion prevalence determined by multiplex qPCR and conventional PCR (cPCR) using existing samples with clonality previously determined by microsatellite genotyping.

METHODS

Multiplex qPCR was used to estimate prevalence of pfhrp2/3 deletions in three sets of previously collected patient samples from Eritrea and Peru. The qPCR was validated by multiplex digital PCR. Sample classification was compared with cPCR, and ROC analysis used to determine the optimal ΔCq threshold that aligned results of the two assays.

RESULTS

qPCR classified 75% (637/849) of samples as single, and 212 as mixed-pfhrp2/3 genotypes, with a positive association between clonality and proportion of mixed-pfhrp2/3 genotype samples. Sample classification agreement between cPCR and qPCR was 75.1% (95% CI 68.6-80.7%) and 47.8% (95% CI 38.9-56.9%) for monoclonal and polyclonal infections. qPCR prevalence estimates of pfhrp2/3 deletions showed almost perfect (κ=0.804; 95% CI 0.714-0.895) and substantial agreement (κ=0.717; 95% CI 0.562-0.872) with cPCR for Peru and 2016 Eritrean samples, respectively. For 2019 Eritrean samples the prevalence of double pfhrp2/3 deletions was approximately two-fold higher using qPCR. The optimal threshold for matching assay results was ΔCq=3.

CONCLUSION

Multiplex qPCR and cPCR produce comparable estimates of gene deletion prevalence when monoclonal infections dominate, but qPCR provides higher estimates where multiclonal infections are common.

A case of possible transfusion-acquired malaria in Zaragoza, Spain

We present the case of a 75-year-old patient diagnosed with malaria, a native of Zaragoza, Spain, despite having no travel history to malaria-endemic regions. Following an extensive investigation, transfusion emerged as the most probable mode of transmission.

Next Generation Chemiluminescent Probes for Antimalarial Drug Discovery

Malaria is caused by parasites of the Plasmodium genus and remains one of the most pressing human health problems. The spread of parasites resistant to or partially resistant to single or multiple drugs, including frontline antimalarial artemisinin and its derivatives, poses a serious threat to current and future malaria control efforts. In vitro drug assays are important for identifying new antimalarial compounds and monitoring drug resistance. Due to its robustness and ease of use, the [3H]-hypoxanthine incorporation assay is still considered a gold standard and is widely applied, despite limited sensitivity and the dependence on radioactive material. Here, we present a first-of-its-kind chemiluminescence-based antimalarial drug screening assay. The effect of compounds on P. falciparum is monitored by using a dioxetane-based substrate (AquaSpark β-D-galactoside) that emits high-intensity luminescence upon removal of a protective group (β-D-galactoside) by a transgenic β-galactosidase reporter enzyme. This biosensor enables highly sensitive, robust, and cost-effective detection of asexual, intraerythrocytic P. falciparum parasites without the need for parasite enrichment, washing, or purification steps. We are convinced that the ultralow detection limit of less than 100 parasites of the presented biosensor system will become instrumental in malaria research, including but not limited to drug screening.

A pH Fingerprint Assay to Identify Inhibitors of Multiple Validated and Potential Antimalarial Drug Targets

New drugs with novel modes of action are needed to safeguard malaria treatment. In recent years, millions of compounds have been tested for their ability to inhibit the growth of asexual blood-stage Plasmodium falciparum parasites, resulting in the identification of thousands of compounds with antiplasmodial activity. Determining the mechanisms of action of antiplasmodial compounds informs their further development, but remains challenging. A relatively high proportion of compounds identified as killing asexual blood-stage parasites show evidence of targeting the parasite's plasma membrane Na+-extruding, H+-importing pump, PfATP4. Inhibitors of PfATP4 give rise to characteristic changes in the parasite's internal [Na+] and pH. Here, we designed a "pH fingerprint" assay that robustly identifies PfATP4 inhibitors while simultaneously allowing the detection of (and discrimination between) inhibitors of the lactate:H+ transporter PfFNT, which is a validated antimalarial drug target, and the V-type H+ ATPase, which was suggested as a possible target of the clinical candidate ZY19489. In our pH fingerprint assays and subsequent secondary assays, ZY19489 did not show evidence for the inhibition of pH regulation by the V-type H+ ATPase, suggesting that it has a different mode of action in the parasite. The pH fingerprint assay also has the potential to identify protonophores, inhibitors of the acid-loading Cl- transporter(s) (for which the molecular identity(ies) remain elusive), and compounds that act through inhibition of either the glucose transporter PfHT or glycolysis. The pH fingerprint assay therefore provides an efficient starting point to match a proportion of antiplasmodial compounds with their mechanisms of action.

Cryogenic electron tomography reveals novel structures in the apical complex of Plasmodium falciparum

Intracellular infectious agents, like the malaria parasite, Plasmodium falciparum, face the daunting challenge of how to invade a host cell. This problem may be even harder when the host cell in question is the enucleated red blood cell, which lacks the host machinery co-opted by many pathogens for internalization. Evolution has provided P. falciparum and related single-celled parasites within the phylum Apicomplexa with a collection of organelles at their apical end that mediate invasion. This apical complex includes at least two sets of secretory organelles, micronemes and rhoptries, and several structural features like apical rings and a putative pore through which proteins may be introduced into the host cell during invasion. We perform cryogenic electron tomography (cryo-ET) equipped with Volta Phase Plate on isolated and vitrified merozoites to visualize the apical machinery. Through tomographic reconstruction of cellular compartments, we see new details of known structures like the rhoptry tip interacting directly with a rosette resembling the recently described rhoptry secretory apparatus (RSA), or with an apical vesicle docked beneath the RSA. Subtomogram averaging reveals that the apical rings have a fixed number of repeating units, each of which is similar in overall size and shape to the units in the apical rings of tachyzoites of Toxoplasma gondii. Comparison of these polar rings in Plasmodium and Toxoplasma parasites also reveals them to have a structurally conserved assembly pattern. These results provide new insight into the essential and structurally conserved features of this remarkable machinery used by apicomplexan parasites to invade their respective host cells.

IMPORTANCE

Malaria is an infectious disease caused by parasites of the genus Plasmodium and is a leading cause of morbidity and mortality globally. Upon infection, Plasmodium parasites invade and replicate in red blood cells, where they are largely protected from the immune system. To enter host cells, the parasites employ a specialized apparatus at their anterior end. In this study, advanced imaging techniques like cryogenic electron tomography (cryo-ET) and Volta Phase Plate enable unprecedented visualization of whole Plasmodium falciparum merozoites, revealing previously unknown structural details of their invasion machinery. Key findings include new insights into the structural conservation of apical rings shared between Plasmodium and its apicomplexan cousin, Toxoplasma. These discoveries shed light on the essential and conserved elements of the invasion machinery used by these pathogens. Moreover, the research provides a foundation for understanding the molecular mechanisms underlying parasite-host interactions, potentially informing strategies for combating diseases caused by apicomplexan parasites.

Plasmodium falciparum selectively degrades α-spectrin of infected erythrocytes after invasion

Remodeling the erythrocyte membrane and skeleton by the malarial parasite Plasmodium falciparum is closely associated with intraerythrocytic development. However, the mechanisms underlying this association remain unclear. In this study, we present evidence that erythrocytic α-spectrin, but not β-spectrin, was dynamically ubiquitinated and progressively degraded during the intraerythrocytic development of P. falciparum, from the ring to the schizont stage. We further observed an upregulated expression of P. falciparum phosphatidylinositol 3-kinase (PfPI3K) in the infected red blood cells during the intraerythrocytic development of the parasite. The data indicated that PfPI3K phosphorylated and activated erythrocytic ubiquitin-protein ligase, leading to increased α-spectrin ubiquitination and degradation during P. falciparum development. We further revealed that inhibition of the activity of PfPI3K impaired P. falciparum development in vitro and Plasmodium berghei infectivity in mice. These findings collectively unveil an important mechanism of PfPI3K-ubiquitin-mediated degradation of α-spectrin during the intraerythrocytic development of Plasmodium species. Proteins in the PfPI3K regulatory pathway are novel targets for effective treatment of severe malaria.

IMPORTANCE

Plasmodium falciparum is the causative agent of severe malaria that causes millions of deaths globally. The parasite invades human red blood cells and induces a cascade of alterations in erythrocytes for development and proliferation. Remodeling the host erythrocytic cytoskeleton is a necessary process during parasitization, but its regulatory mechanisms remain to be elucidated. In this study, we observed that erythrocytic α-spectrin is selectively degraded after P. falciparum invasion, while β-spectrin remained intact. We found that the α-spectrin chain was profoundly ubiquitinated by E3 ubiquitin ligase and degraded by the 26S proteasome. E3 ubiquitin ligase activity was regulated by P. falciparum phosphatidylinositol 3-kinase (PfPI3K) signaling. Additionally, blocking the PfPI3K-ubiquitin-proteasome pathway in P. falciparum-infected red blood cells reduced parasite proliferation and infectivity. This study deepens our understanding of the regulatory mechanisms of host and malarial parasite interactions and paves the way for the exploration of novel antimalarial drugs.

Usefulness of serial testing for the diagnosis of malaria in cases of fever upon return from travel

BACKGROUND

When malaria is suspected in case of fever after travel in endemic areas, the current recommendation is to repeat the malaria test at 24-hour intervals, with up to two additional tests, as long as the test result is negative. A retrospective analysis was conducted to investigate the appropriateness of this recommendation by determining the proportion of tests with negative result at first and subsequently with a positive one at second or third attempt.

METHODS

A retrospective study was conducted at the Centre for Primary Care and Public Health, Lausanne, covering a period of 15 years. All patients tested once for malaria were included. Testing included microscopy thick and thin films as well as malaria rapid diagnostic test used in combination. The main outcome measure was the proportion of patients with a first negative test result, subsequently positive on second or third test over the total patients with suspected malaria assessed. Demographic, travel, clinical, and laboratory variables were collected from patients' records to identify potential predictors of an initially negative and then positive test result.

RESULTS

Four thousand nine hundred seventy-two patients were included. Of those, 4557 (91.7%) had definitive negative test results, and 415 (8.3%) had a positive result on the first test [332/415 (80%) Plasmodium falciparum, 40/415 (9.6%) P. vivax, 21/415 (5.1%) P. ovale, 12/415 (2.9%) P. vivax/ovale, 9/415 (2.2%) P. malariae and 1/415 (0.2%) P. knowlesi], and 3/4972 (0.06%) had a positive result on the second test after a first negative result, 1/4972(0.02%) had a positive test result after 2 negative results, all with P. falciparum. One of the four patients that were positive after their initial negative test was pregnant. The very small number of patients with an initially negative test result and secondarily positive did not allow for risk factor analysis.

CONCLUSIONS

The current recommendation of serial malaria testing is not supported by the present study, a fortiori for those who do not present with a strong clinical or laboratory predictor of malaria.

A paradigm for Africa-centric vaccine development in Equatorial Guinea

The Equatorial Guinea Malaria Vaccine Initiative (EGMVI) highlights how long-term African government and international energy industry investment, plus novel partnerships, can enable clinical development of vaccines in Africa, for Africa. We review achievements and challenges of this pioneering, award-winning, public-private partnership which offers a model for future Africa-centric clinical research and development (R&D).

A severe case of Plasmodium falciparum malaria in a traveler returning from Kazakhstan, a malaria-free country

Following a two-weeks trip to Kazakhstan, a 42-year-old woman presented at the emergency department in Germany with fever, headache, nausea, and neurological symptoms. An infection with Plasmodium falciparum was rapidly diagnosed. The patient was immediately treated with intravenous artesunate and transferred to an intensive care unit. The initial parasite density was as high as 30% infected erythrocytes with 845880 parasites/µL. Since Kazakhstan was declared malaria-free in 2012, molecular testing for Plasmodium has been initiated to identify a possible origin. Genotyping of the msp-1 gene and microsatellite markers showed that the parasites are of African origin, with two different alleles indicating a polyclonal infection. After a hospitalization of 10 days, the patient was discharged in good health. Overall, our results emphasize that malaria must be on the list of differential diagnoses for patients with fever of unknown origin, even if they come from countries where malaria does not commonly occur.

Ex vivo drug susceptibility and resistance mediating genetic polymorphisms of Plasmodium falciparum in Bobo-Dioulasso, Burkina Faso

Malaria remains a leading cause of morbidity and mortality in Burkina Faso, which utilizes artemether-lumefantrine as the principal therapy to treat uncomplicated malaria and seasonal malaria chemoprevention with monthly sulfadoxine-pyrimethamine plus amodiaquine in children during the transmission season. Monitoring the activities of available antimalarial drugs is a high priority. We assessed the ex vivo susceptibility of Plasmodium falciparum to 11 drugs in isolates from patients presenting with uncomplicated malaria in Bobo-Dioulasso in 2021 and 2022. IC50 values were derived using a standard 72 h growth inhibition assay. Parasite DNA was sequenced to characterize known drug resistance-mediating polymorphisms. Isolates were generally susceptible, with IC50 values in the low-nM range, to chloroquine (median IC5010 nM, IQR 7.9-24), monodesethylamodiaquine (22, 14-46) piperaquine (6.1, 3.6-9.2), pyronaridine (3.0, 1.3-5.5), quinine (50, 30-75), mefloquine (7.1, 3.7-10), lumefantrine (7.1, 4.5-12), dihydroartemisinin (3.7, 2.2-5.5), and atovaquone (0.2, 0.1-0.3) and mostly resistant to cycloguanil (850, 543-1,290) and pyrimethamine (33,200, 18,400-54,200), although a small number of outliers were seen. Considering genetic markers of resistance to aminoquinolines, most samples had wild-type PfCRT K76T (87%) and PfMDR1 N86Y (95%) sequences. For markers of resistance to antifolates, established PfDHFR and PfDHPS mutations were highly prevalent, the PfDHPS A613S mutation was seen in 19% of samples, and key markers of high-level resistance (PfDHFR I164L; PfDHPS K540E) were absent or rare (A581G). Mutations in the PfK13 propeller domain known to mediate artemisinin partial resistance were not detected. Overall, our results suggest excellent susceptibilities to drugs now used to treat malaria and moderate, but stable, resistance to antifolates used to prevent malaria.

Revisiting the determinants of malaria transmission

Malaria parasites have coevolved with humans over thousands of years, mirroring their migration out of Africa. They persist to this day, despite continuous elimination efforts worldwide. These parasites can adapt to changing environments during infection of human and mosquito, and when expanding the geographical range by switching vector species. Recent studies in the human malaria parasite, Plasmodium falciparum, identified determinants governing the plasticity of sexual conversion rates, sex ratio, and vector competence. Here we summarize the latest literature revealing environmental, epigenetic, and genetic determinants of malaria transmission.

Absence of association between Pfnfs1 mutation and in vitro susceptibility to lumefantrine in Plasmodium falciparum

Artemether-lumefantrine (AL) is the most widely used antimalarial drug for treating uncomplicated falciparum malaria. This study evaluated whether the K65Q mutation in the Plasmodium falciparum cysteine desulfurase IscS (Pfnfs1) gene was associated with alternated susceptibility to lumefantrine using clinical parasite samples from Ghana and the China-Myanmar border area. Parasite isolates from the China-Myanmar border had significantly higher IC50 values to lumefantrine than parasites from Ghana. In addition, the K65 allele was significantly more prevalent in the Ghanaian parasites (34.5%) than in the China-Myanmar border samples (6.8%). However, no difference was observed in the lumefantrine IC50 value between the Pfnfs1 reference K65 allele and the non reference 65Q allele in parasites from the two regions. These data suggest that the Pfnfs1 K65Q mutation may not be a reliable marker for reduced susceptibility to lumefantrine.

Immune tolerance caused by repeated P. falciparum infection against SE36 malaria vaccine candidate antigen and the resulting limited polymorphism

The call for second generation malaria vaccines needs not only the identification of novel candidate antigens or adjuvants but also a better understanding of immune responses and the underlying protective processes. Plasmodium parasites have evolved a range of strategies to manipulate the host immune system to guarantee survival and establish parasitism. These immune evasion strategies hamper efforts to develop effective malaria vaccines. In the case of a malaria vaccine targeting the N-terminal domain of P. falciparum serine repeat antigen 5 (SE36), now in clinical trials, we observed reduced responsiveness (lowered immunogenicity) which may be attributed to immune tolerance/immune suppression. Here, immunogenicity data and insights into the immune responses to SE36 antigen from epidemiological studies and clinical trials are summarized. Documenting these observations is important to help identify gaps for SE36 continued development and engender hope that highly effective blood-stage/multi-stage vaccines can be achieved.

Imported malaria: A 20-year retrospective study from a tertiary public hospital in Brussels, Belgium

BACKGROUND

Malaria continues to cause a significant number of infections in non-endemic regions. In this paper, we describe the epidemiological trend and morbidity of imported malaria diagnosed in a tertiary hospital in Brussels.

METHODS

We conducted a retrospective study describing a cohort of malaria episodes (in- and outpatients) at Centre Hospitalier Universitaire Saint-Pierre from 1998 to 2017. Epidemiological and clinical data were collected by reviewing medical files.

RESULTS

A total of 1011 malaria episodes were analyzed. Median age at diagnosis was 35 years, and 66 % of patients were men (672/1011). Malaria cases significantly increased over the two decades (from 17 in 1998 to 79 in 2017). Plasmodium falciparum malaria was most often diagnosed (846/935, 89 %), primarily from Central (530/935, 57 %) and West Africa (324/935, 35 %). Many cases (383/764, 50 %) were diagnosed in patients "visiting friends and relatives". HIV-infected and other immunocompromised patients were significantly more likely to present with severe malaria (at least one severity criteria as defined by the WHO) compared to other patients (24/57, 42 % vs 138/732, 19 %, p < 0.01 and 15/21, 71 % vs 147/767, 19 %, p < 0.001). Severe malaria was diagnosed in 16.9 % and the mortality rate was low (5/1011, 0.5 %).

CONCLUSION

Imported malaria increased over the years with a large, albeit stable number of cases diagnosed in patients visiting friends and relatives. These findings, along with the high rate of severe malaria in HIV and immunocompromised patients, underscore an urgent need for strengthened malaria surveillance and targeted preventive interventions.

Plasmodium falciparum heat shock proteins as antimalarial drug targets: An update

Global efforts to eradicate malaria are threatened by multiple factors, particularly the emergence of antimalarial drug resistant strains of Plasmodium falciparum. Heat shock proteins (HSPs), particularly P. falciparum HSPs (PfHSPs), represent promising drug targets due to their essential roles in parasite survival and virulence across the various life cycle stages. Despite structural similarities between human and malarial HSPs posing challenges, there is substantial evidence for subtle differences that could be exploited for selective drug targeting. This review provides an update on the potential of targeting various PfHSP families (particularly PfHSP40, PfHSP70, and PfHSP90) and their interactions within PfHSP complexes as a strategy to develop new antimalarial drugs. In addition, the need for a deeper understanding of the role of HSP complexes at the host-parasite interface is highlighted, especially heterologous partnerships between human and malarial HSPs, as this opens novel opportunities for targeting protein-protein interactions crucial for malaria parasite survival and pathogenesis.

Plasmodium falciparum proteases as new drug targets with special focus on metalloproteases

Malaria poses a significant global health threat particularly due to the prevalence of Plasmodium falciparum infection. With the emergence of parasite resistance to existing drugs including the recently discovered artemisinin, ongoing research seeks novel therapeutic avenues within the malaria parasite. Proteases are promising drug targets due to their essential roles in parasite biology, including hemoglobin digestion, merozoite invasion, and egress. While exploring the genomic landscape of Plasmodium falciparum, it has been revealed that there are 92 predicted proteases, with only approximately 14 of them having been characterized. These proteases are further distributed among 26 families grouped into five clans: aspartic proteases, cysteine proteases, metalloproteases, serine proteases, and threonine proteases. Focus on metalloprotease class shows further role in organelle processing for mitochondria and apicoplasts suggesting the potential of metalloproteases as viable drug targets. Holistic understanding of the parasite intricate life cycle and identification of potential drug targets are essential for developing effective therapeutic strategies against malaria and mitigating its devastating global impact.

A case of babesiosis in a returning traveller

Human babesiosis data in Africa is scarce. The clinical presentation and parasite morphology mimics falciparum malaria infection. Diagnostic confirmation is informed by adequate history and communication with the laboratory to activate appropriate testing. This case report describes the course of a returning traveller with persisting symptoms that resolved on tailored antimicrobial therapy following prompt collaborative diagnosis.

Contribution

Case highlighting overlapping characteristics of Babesia and malaria infection, necessitating close clinical and laboratory correlation to confirm diagnosis.

Real-time measurements of ATP dynamics via ATeams in Plasmodium falciparum reveal drug-class-specific response patterns

Malaria tropica, caused by the parasite Plasmodium falciparum (P. falciparum), remains one of the greatest public health burdens for humankind. Due to its pivotal role in parasite survival, the energy metabolism of P. falciparum is an interesting target for drug design. To this end, analysis of the central metabolite adenosine triphosphate (ATP) is of great interest. So far, only cell-disruptive or intensiometric ATP assays have been available in this system, with various drawbacks for mechanistic interpretation and partly inconsistent results. To address this, we have established fluorescent probes, based on Förster resonance energy transfer (FRET) and known as ATeam, for use in blood-stage parasites. ATeams are capable of measuring MgATP2- levels in a ratiometric manner, thereby facilitating in cellulo measurements of ATP dynamics in real-time using fluorescence microscopy and plate reader detection and overcoming many of the obstacles of established ATP analysis methods. Additionally, we established a superfolder variant of the ratiometric pH sensor pHluorin (sfpHluorin) in P. falciparum to monitor pH homeostasis and control for pH fluctuations, which may affect ATeam measurements. We characterized recombinant ATeam and sfpHluorin protein in vitro and stably integrated the sensors into the genome of the P. falciparum NF54attB cell line. Using these new tools, we found distinct sensor response patterns caused by several different drug classes. Arylamino alcohols increased and redox cyclers decreased ATP; doxycycline caused first-cycle cytosol alkalization; and 4-aminoquinolines caused aberrant proteolysis. Our results open up a completely new perspective on drugs' mode of action, with possible implications for target identification and drug development.

In silico screening of selective ATP mimicking inhibitors targeting the Plasmodium falciparum Grp94

Plasmodium falciparum parasites export more than 400 proteins to remodel the host cell environment and increase its chances of surviving and reproducing. The endoplasmic reticulum (ER) plays a central role in protein export by facilitating protein sorting and folding. The ER resident member of the Hsp90 family, glucose-regulated protein 94 (Grp94), is a molecular chaperone that facilitates the proper folding of client proteins in the ER lumen. In P. falciparum, Grp94 (PfGrp94) is essential for parasite survival, rendering it a promising anti-malarial drug target. Despite this, its druggability has not been fully explored. Consequently, this study sought to identify small molecule inhibitors targeting the PfGrp94. Potential small molecule inhibitors of PfGrp94 were designed and screened using in silico studies. Molecular docking studies indicate that two novel compounds, Compound S and Compound Z selectively bind to PfGrp94 over its human homologues. Comparatively, Compound Z had a higher affinity for PfGrp94 than Compound S. Further interrogation of the inhibitor binding using molecular dynamics (MD) analysis confirmed that Compound Z formed stable binding poses within the ATP-binding pocket of the PfGrp94 N-terminal domain (NTD) during the 250 ns simulation run. PfGrp94 interacted with Compound Z through hydrogen bonding and hydrophobic interactions with residues Asp 148, Asn 106, Gly 152, Ile 151 and Lys 113. Based on the findings of this study, Compound Z could serve as a competitive and selective inhibitor of PfGrp94 and may be useful as a starting point for the development of a potential drug for malaria.Communicated by Ramaswamy H. Sarma.

Dynamics of Plasmodium species and genotype diversity in adults with asymptomatic infection in Gabon

OBJECTIVES

We investigated the diversity and dynamics of Plasmodium infection in serially collected samples from asymptomatic participants of a clinical trial assessing the efficacy and safety of ivermectin in Gabon. We checked whether the baseline sample reflected the P. falciparum genotype and Plasmodium species diversity seen over 7 days of follow-up.

METHODS

Blood samples were collected at inclusion, every 8 hours until hour 72, daily until day 7, and on day 14. Plasmodium species was determined by qPCR and pfmsp1 length polymorphism was assessed for P. falciparum genotyping.

RESULTS

In 17/48 (35%) individuals, all pfmsp1 genotypes identified during the assessed period were detected at baseline; in 31/48 (65%), new genotypes were found during follow-up. Additional sampling at hour 24 allowed the identification of all genotypes seen over 7 days in 50% of the individuals. Ivermectin did not impact the genotype dynamics. Mixed Plasmodium spp. infections were detected in 28/49 (57%) individuals at baseline, and detection of non-falciparum infections during follow-up varied.

CONCLUSIONS

Our results reveal complex intra-host dynamics of P. falciparum genotypes and Plasmodium species and underscore the importance of serial sampling in clinical trials for antimalarial drugs with asymptomatically P. falciparum-infected individuals. This might allow a more accurate identification of genotypes in multiple infections, impacting the assessment of drug efficacy.

Malaria vaccination: hurdles to reach high-risk children

Ensuring that malaria vaccines deliver maximum public health impact is non-trivial. Drawing on current research, this article examines hurdles that malaria immunization may face to reach high-risk children and explores the policy implications. The analysis finds health system related risks with the potential to reduce the ability of malaria vaccines to provide equitable protection. Deployment of effective frameworks to tackle these risks so as to strengthen within-country equity and progress tracking should be entangled with the deployment of the vaccines. To capture more comprehensively disease- and system-related risks to child health and survival, vaccine allocation criteria should expand their data and indicator breadth. Factoring molecular, clinical, and epidemiological features of antimalarial drug resistance into vaccine allocation frameworks is critical to effectively reflect current and future risks to malaria control interventions. It is proposed that approximately 6-15 children would need to be vaccinated to prevent a malaria adverse outcome. Vaccine purchasing and delivery costs may overwhelm endemic countries' health systems given the sizeable number needed to vaccinate, the population of at-risk children, and limited government financing of the health sector. Innovations in health financing are pivotal to ensuring the cost-effectiveness and sustainability of immunization programs aiming to attain and maintain universal and equitable protection.

High Target Homology Does Not Guarantee Inhibition: Aminothiazoles Emerge as Inhibitors of Plasmodium falciparum

In this study, we identified three novel compound classes with potent activity against Plasmodium falciparum, the most dangerous human malarial parasite. Resistance of this pathogen to known drugs is increasing, and compounds with different modes of action are urgently needed. One promising drug target is the enzyme 1-deoxy-d-xylulose-5-phosphate synthase (DXPS) of the methylerythritol 4-phosphate (MEP) pathway for which we have previously identified three active compound classes against Mycobacterium tuberculosis. The close structural similarities of the active sites of the DXPS enzymes of P. falciparum and M. tuberculosis prompted investigation of their antiparasitic action, all classes display good cell-based activity. Through structure-activity relationship studies, we increased their antimalarial potency and two classes also show good metabolic stability and low toxicity against human liver cells. The most active compound 1 inhibits the growth of blood-stage P. falciparum with an IC50 of 600 nM. The results from three different methods for target validation of compound 1 suggest no engagement of DXPS. All inhibitor classes are active against chloroquine-resistant strains, confirming a new mode of action that has to be further investigated.

Genetic complexity alters drug susceptibility of asexual and gametocyte stages of Plasmodium falciparum to antimalarial candidates

Malaria elimination requires interventions able to target both the asexual blood stage (ABS) parasites and transmissible gametocyte stages of Plasmodium falciparum. Lead antimalarial candidates are evaluated against clinical isolates to address key concerns regarding efficacy and to confirm that the current, circulating parasites from endemic regions lack resistance against these candidates. While this has largely been performed on ABS parasites, limited data are available on the transmission-blocking efficacy of compounds with multistage activity. Here, we evaluated the efficacy of lead antimalarial candidates against both ABS parasites and late-stage gametocytes side-by-side, against clinical P. falciparum isolates from southern Africa. We additionally correlated drug efficacy to the genetic diversity of the clinical isolates as determined with a panel of well-characterized, genome-spanning microsatellite markers. Our data indicate varying sensitivities of the isolates to key antimalarial candidates, both for ABS parasites and gametocyte stages. While ABS parasites were efficiently killed, irrespective of genetic complexity, antimalarial candidates lost some gametocytocidal efficacy when the gametocytes originated from genetically complex, multiple-clone infections. This suggests a fitness benefit to multiclone isolates to sustain transmission and reduce drug susceptibility. In conclusion, this is the first study to investigate the efficacy of antimalarial candidates on both ABS parasites and gametocytes from P. falciparum clinical isolates where the influence of parasite genetic complexity is highlighted, ultimately aiding the malaria elimination agenda.

A Dangerous Relationship: A Case of Imported Plasmodium falciparum and Salmonella Typhi Coinfection

Malaria is a parasitic disease transmitted by the bite of female Anopheles mosquitoes. Although domestic malaria case notification in our country is not seen in World Health Organization records, cases originating from abroad are detected. Travelers to countries where malaria is endemic can become infected with the parasite. In our country, an average of 200-250 cases of malaria originating from abroad are reported every year. Approximately 75% of malaria cases of foreign origin detected in our country are P. falciparum malaria. Malaria and salmonellosis are infections especially seen in developing countries. Although malaria-Salmonella coinfection is rare, early diagnosis and treatment are important in terms of its high mortality rate. Preliminary information and initiation of chemoprophylaxis in travels to regions where the disease is endemic remain important in transmission. In this presentation, a case was examined following a business trip to Africa without any chemoprophylaxis, who applied to a local hospital upon symptoms and was diagnosed with P. falciparum and Salmonella Typhi coinfection but given incomplete treatment. After returning to our country, the patient applying to us with complaints of high fever, chills, nausea, diarrhea and abdominal pain and was discharged with ful recovery.

Molecular modelling approaches can reveal the Molecular interactions established between antimalarial targets of hemozoin pathway and the organic phytochemicals of Artocarpus species

Ayurveda, the traditional Indian medical system, has potential applications in early malaria treatment. In an in silico docking study, 50 phytochemicals from two plants Artocarpus lakoocha Roxb. (AL) And Artocarpus heterophyllus Lam. (AH), were examined for their interactions with anti-malarial proteins (PDB IDs: 3BWK, 3BPF, 1LF3). The nucleotide analogue Artemisinin, a current malaria treatment, served as a positive control. Result showed that phytochemicals from AL and AH exhibited binding affinities as high as -9.6 kcal/mol, respectively. Additionally, molecular dynamics simulation for Artocarpin: 3BPF demonstrated stable complexes over 100 ns. Notably, Artocarpin and Quercetin displayed higher binding affinities (up to -9.6 as well as -9.5 kcal/mol, respectively) compared to Artemisinin (-7.5 up to kcal/mol), have shown. Pharmacokinetic predictions indicated the compounds were likely non-carcinogenic, water-soluble and biologically safe. In-vitro analysis using β-Hematin assay supported these findings, suggesting the phytochemicals as Hemozoin pathway inhibitors.

Increase of Plasmodium falciparum parasites carrying lumefantrine-tolerance molecular markers and lack of South East Asian pfk13 artemisinin-resistance mutations in samples collected from 2013 to 2016 in Côte d'Ivoire

One of the major obstacles to malaria elimination in the world is the resistance in Plasmodium falciparum to most antimalarial drugs. This study aimed to estimate the prevalence of molecular markers of antimalarial drugs resistance in Côte d'Ivoire. Samples were collected from 2013 to 2016 from asymptomatic and symptomatic subjects in Abengourou, Abidjan, Grand Bassam, and San Pedro. A total of 704 participants aged between 1 year and 65 years (Mean age: 9 years ± 7.7) were enrolled. All the dried filter paper blood spots were genotyped by sequencing. Plasmodium falciparum kelch propeller domain 13 (pfk13) gene were analyzed for all the samples, while 344 samples were examined for Plasmodium falciparum multi-drug resistance 1 (pfmdr1). Overall, the success rate of molecular tests was 98.8% (340/344), 99.1% (341/344), and 94.3% (664/704) for pfmdr1 N86Y, pfmdr1 Y184F, and pfk13 genes respectively. Molecular analysis revealed twenty (5.9%; 20/340) and 219 (64.2%; 219/341) mutant alleles for pfmdr1 86Y and pfmdr1 184 F, respectively. Twenty-nine mutations in pfk13 gene (4.4%; 29/664) with 2.7% (18/664) of non-synonymous mutations was found. None of the mutations previously described in South East Asia (SEA) involved in P. falciparum resistance to artemisinin derivatives were observed in this study. According to year of collection, a decrease of the prevalence of pfk13 mutation (from 3.6 to 1.8%) and pfmdr1 N86Y mutation (from 8.5 to 4.5%) and an increase of mutant allele of pfmdr1 Y184F proportion (from 39.8 to 66.4%) were found. Comparing to previous studies in the country, this study showed an increase in lumefantrine tolerance of P. falciparum strains. This demonstrates the importance of establishing a strong system for molecular surveillance of malaria in Côte d'Ivoire.

Association between asymptomatic Plasmodium falciparum malaria infection, anaemia and mean corpuscular volume of school children in the Volta Region of Ghana

Background

Although, several studies have reported abnormal Mean Corpuscular Volume (MCV) values and anaemia associated with malaria infections with a focus on Plasmodium falciparum among patients with complicated and uncomplicated malaria, none has looked at the association with asymptomatic malaria. This study aimed to assess this association.

Methods

We conducted a cross-sectional study using 3 mL of blood samples from 549 children aged 5-17 years attending 5 schools selected in the Volta Region. Semi-structured questionnaires were administered to the children to obtain demographic data. Blood samples were collected to estimate the children's full blood count (FBC) and malaria status. Data obtained were analysed using STATA 15 software. P-values of less than 0.05 were considered statistically significant.

Results

Most of the children in this study (49.9%) had normal MCV (81.3-91.3 fL) with an overall malaria prevalence of 55.6 % (95% CI: 51.3-59.8) and anaemia prevalence of 48.6% (95% CI 44.4-52.9). Most anaemic children had normal MCV (81.3-91.3 fL) (49.8, 95% CI 43.7-56.0). The predicted probability of malaria was highly likely among children with normal MCV (81.3-91.3 fL) but with high variability and uncertainty among those with low MCV (<81.3 fL) and high MCV (>91.3 fL).

Conclusion

This study shows a reduced predicted probability of malaria among children with low and high MCV, playing a protective function against malaria. Further studies are required to elucidate the interaction.

Molecular Players at the Sorting Stations of Malaria Parasite 'Plasmodium falciparum'

The apicomplexan pathogenic parasite 'Plasmodium falciparum' (Pf) is responsible for most of the malaria related mortality. It resides in and refurbishes the infected red blood cells (iRBCs) for its own survival and to suffice its metabolic needs. Remodeling of host erythrocytes involves alteration of physical and biochemical properties of the membrane and genesis of new parasite induced structures within the iRBCs. The generated structures include knobs and solute ion channels on the erythrocyte surface and specialized organelles i.e. Maurer's clefts (MCs) in the iRBC cytosol. The above processes are mediated by exporting a large repertoire of proteins to the host cell, most of which are transported via MCs, the sorting stations in parasitized erythrocytes. Information about MC biogenesis and the molecules involved in maintaining MC architecture remains incompletely elucidated. Here, we have compiled a list of experimentally known MC resident proteins, several of which have roles in maintaining its architecture and function. Our short review covers available data on the domain organization, orthologues, topology and specific roles of these proteins. We highlight the current knowledge gaps in our understanding of MCs as crucial organelles involved in parasite biology and disease pathogenesis.

IgG Subclass Switch in Volunteers Repeatedly Immunized with the Full-Length Plasmodium falciparum Merozoite Surface Protein 1 (MSP1)

Vaccines are highly effective tools against infectious diseases and are also considered necessary in the fight against malaria. Vaccine-induced immunity is frequently mediated by antibodies. We have recently conducted a first-in-human clinical trial featuring SumayaVac-1, a malaria vaccine based on the recombinant, full-length merozoite surface protein 1 (MSP1FL) formulated with GLA-SE as an adjuvant. Vaccination with MSP1FL was safe and elicited sustainable IgG antibody titers that exceeded those observed in semi-immune populations from Africa. Moreover, IgG antibodies stimulated various Fc-mediated effector mechanisms associated with protection against malaria. However, these functionalities gradually waned. Here, we show that the initial two doses of SumayaVac-1 primarily induced the cytophilic subclasses IgG1 and IgG3. Unexpectedly, a shift in the IgG subclass composition occurred following the third and fourth vaccinations. Specifically, there was a progressive transition to IgG4 antibodies, which displayed a reduced capacity to engage in Fc-mediated effector functions and also exhibited increased avidity. In summary, our analysis of antibody responses to MSP1FL vaccination unveils a temporal shift towards noninflammatory IgG4 antibodies. These findings underscore the importance of considering the impact of IgG subclass composition on vaccine-induced immunity, particularly concerning Fc-mediated effector functions. This knowledge is pivotal in guiding the design of optimal vaccination strategies against malaria, informing decision making for future endeavors in this critical field.

Subcellular particles for characterization of host-parasite interactions

Parasitic diseases remain a major global health problem for humans. Parasites employ a variety of strategies to invade and survive within their hosts and to manipulate host defense mechanisms, always in the pathogen's favor. Extracellular vesicles (EVs), membrane-bound nanospheres carrying a variety of bioactive compounds, were shown to be released by the parasites during all stages of the infection, enabling growth and expansion within the host and adaptation to frequently changing environmental stressors. In this review, we discuss how the use of existing nanotechnologies and high-resolution imaging tools assisted in revealing the role of EVs during parasitic infections, enabling the quantitation, visualization, and detailed characterization of EVs. We discuss here the cases of malaria, Chagas disease and leishmaniasis as examples of parasitic neglected tropical diseases (NTDs). Unraveling the EVs' role in the NTD pathogenesis may enormously contribute to their early and reliable diagnostic, effective treatment, and prevention.

Antibody-Dependent Respiratory Burst against Plasmodium falciparum Merozoites in Individuals Living in an Area with Declining Malaria Transmission

Malaria transmission intensity affects the development of naturally acquired immunity to malaria. An absolute correlate measure of protection against malaria is lacking. However, antibody-mediated functions against Plasmodium falciparum correlate with protection against malaria. In children, antibody-mediated functions against P. falciparum decline with reduced exposure. It is unclear whether adults maintain antibody-mediated functions as malaria transmission declines. This study assessed antibody-dependent respiratory burst (ADRB) in individuals from an area with declining malaria transmission. In an age-matched analysis, we compare ADRB activity during high versus low malaria transmission periods. Age significantly predicted higher ADRB activity in the high (p < 0.001) and low (p < 0.001) malaria transmission periods. ADRB activity was higher during the high compared to the low malaria transmission period in older children and adults. Only older adults during the high malaria transmission period had their median ADRB activity above the ADRB cut-off. Ongoing P. falciparum infection influenced ADRB activity during the low (p = 0.01) but not the high (p = 0.29) malaria transmission period. These findings propose that naturally acquired immunity to P. falciparum is affected in children and adults as malaria transmission declines, implying that vaccines will be necessary to induce and maintain protection against malaria.

Classification and clinical significance of immunogenic cell death-related genes in Plasmodium falciparum infection determined by integrated bioinformatics analysis and machine learning

BACKGROUND

Immunogenic cell death (ICD) is a type of regulated cell death that plays a crucial role in activating the immune system in response to various stressors, including cancer cells and pathogens. However, the involvement of ICD in the human immune response against malaria remains to be defined.

METHODS

In this study, data from Plasmodium falciparum infection cohorts, derived from cross-sectional studies, were analysed to identify ICD subtypes and their correlation with parasitaemia and immune responses. Using consensus clustering, ICD subtypes were identified, and their association with the immune landscape was assessed by employing ssGSEA. Differentially expressed genes (DEGs) analysis, functional enrichment, protein-protein interaction networks, and machine learning (least absolute shrinkage and selection operator (LASSO) regression and random forest) were used to identify ICD-associated hub genes linked with high parasitaemia. A nomogram visualizing these genes' correlation with parasitaemia levels was developed, and its performance was evaluated using receiver operating characteristic (ROC) curves.

RESULTS

In the P. falciparum infection cohort, two ICD-associated subtypes were identified, with subtype 1 showing better adaptive immune responses and lower parasitaemia compared to subtype 2. DEGs analysis revealed upregulation of proliferative signalling pathways, T-cell receptor signalling pathways and T-cell activation and differentiation in subtype 1, while subtype 2 exhibited elevated cytokine signalling and inflammatory responses. PPI network construction and machine learning identified CD3E and FCGR1A as candidate hub genes. A constructed nomogram integrating these genes demonstrated significant classification performance of high parasitaemia, which was evidenced by AUC values ranging from 0.695 to 0.737 in the training set and 0.911 to 0.933 and 0.759 to 0.849 in two validation sets, respectively. Additionally, significant correlations between the expressions of these genes and the clinical manifestation of P. falciparum infection were observed.

CONCLUSION

This study reveals the existence of two ICD subtypes in the human immune response against P. falciparum infection. Two ICD-associated candidate hub genes were identified, and a nomogram was constructed for the classification of high parasitaemia. This study can deepen the understanding of the human immune response to P. falciparum infection and provide new targets for the prevention and control of malaria.

Biological evaluation of novel side chain containing CQTrICh-analogs as antimalarials and their development as PfCDPK1 kinase inhibitors

The rapid emergence of resistance to existing frontline antimalarial drugs emphasizes a need for the development of target-oriented molecules with novel modes of action. Given the importance of a plant-like Calcium-Dependent Protein Kinase 1 (PfCDPK1) as a stand-alone multistage signalling regulator of P. falciparum, we designed and synthesized 7-chloroquinoline-indole-chalcones tethered with a triazole (CQTrICh-analogs 7 (a-s) and 9) directed towards PfCDPK1. This was accomplished by reacting substituted 1-phenyl-3-(1-(prop-2-yn-1-yl)-1H-indol-3-yl) prop-2-en-1-one and 1-(prop-2-yn-1-yl)-1H-indole-3-carbaldehyde with 4-azido-7-chloroquinoline, respectively via a 'click' reaction. The selected CQTrICh-analogs: 7l and 7r inhibited the growth of chloroquine-sensitive 3D7 strain and -resistant RKL-9 isolate of Plasmodium falciparum, with IC50 values of 2.4 μM & 1.8 μM (7l), and 3.5 μM & 2.7 μM (7r), respectively, and showed no apparent hemolytic activity and cytotoxicity in mammalian cells. Intra-erythrocytic progression studies revealed that the active hybrids: 7l and 7r are effective against the mature stages of the parasite. 7l and 7r were found to stably interact with the catalytically active ATP-binding pocket of PfCDPK1 via energetically favourable H-bonds. The interaction was confirmed in vitro by microscale thermophoresis and kinase assays, which demonstrated that the active hybrids interact with PfCDPK1 and inhibit its kinase activity which is presumably responsible for the parasite growth inhibition. Interestingly, 7l and 7r showed no inhibitory effect on the human kinases, indicating their selectivity for the parasite kinase. We report the antiplasmodial potential of novel kinase-targeting bio-conjugates, a step towards developing pan-kinase inhibitors which is a prerequisite for multistage anti-malarial protection.

Strong isolation by distance and evidence of population microstructure reflect ongoing Plasmodium falciparum transmission in Zanzibar

The Zanzibar archipelago of Tanzania has become a low-transmission area for Plasmodium falciparum. Despite being considered an area of pre-elimination for years, achieving elimination has been difficult, likely due to a combination of imported infections from mainland Tanzania, and continued local transmission. To shed light on these sources of transmission, we applied highly multiplexed genotyping utilizing molecular inversion probes to characterize the genetic relatedness of 282 P. falciparum isolates collected across Zanzibar and in Bagamoyo District on the coastal mainland from 2016-2018. Overall, parasite populations on the coastal mainland and Zanzibar archipelago remain highly related. However, parasite isolates from Zanzibar exhibit population microstructure due to rapid decay of parasite relatedness over very short distances. This, along with highly related pairs within shehias, suggests ongoing low level local transmission. We also identified highly related parasites across shehias that reflect human mobility on the main island of Unguja and identified a cluster of highly related parasites, suggestive of an outbreak, in the Micheweni district on Pemba island. Parasites in asymptomatic infections demonstrated higher complexity of infection than those in symptomatic infections, but have similar core genomes. Our data support importation as a main source of genetic diversity and contribution to the parasite population on Zanzibar, but they also show local outbreak clusters where targeted interventions are essential to block local transmission. These results highlight the need for preventive measures against imported malaria and enhanced control measures in areas that remain receptive for malaria reemergence due to susceptible hosts and competent vectors.

Genomics reveals heterogeneous Plasmodium falciparum transmission and population differentiation in Zambia and bordering countries

Genomic surveillance plays a critical role in monitoring malaria transmission and understanding how the parasite adapts in response to interventions. We conducted genomic surveillance of malaria by sequencing 241 Plasmodium falciparum genomes from regions with varying levels of malaria transmission across Zambia. We found genomic evidence of high levels of within-host polygenomic infections, regardless of epidemiological characteristics, underscoring the extensive and ongoing endemic malaria transmission in the country. We identified country-level clustering of parasites from Zambia and neighboring countries, and distinct clustering of parasites from West Africa. Within Zambia, our identity by descent (IBD) relatedness analysis uncovered spatial clustering of closely related parasite pairs at the local level and rare cases of long-distance sharing. Genomic regions with large shared IBD segments and strong positive selection signatures identified genes involved in sulfadoxine-pyrimethamine and artemisinin combination therapies drug resistance, but no signature related to chloroquine resistance. Together, our findings enhance our understanding of P. falciparum transmission nationwide in Zambia and highlight the urgency of strengthening malaria control programs and surveillance of antimalarial drug resistance.

Mutation in the 26S proteasome regulatory subunit rpn2 gene in Plasmodium falciparum confers resistance to artemisinin

Introduction

Malaria parasites increasingly develop resistance to all drugs available in the market, hampering the goal of reducing malaria burden.

Methods

Herein, we evaluated the impact of a single-nucleotide variant, E738K, present in the 26S proteasome regulatory subunit rpn2 gene, identified in Plasmodium chabaudi resistant parasites. Plasmids carrying a functional rpn2 interspecies chimeric gene with 5' recombination region from P. falciparum and 3' from P. chabaudi were constructed and transfected into Dd2 P. falciparum parasites.

Results and discussion

The 738K variant parasite line presented increased parasite survival when subjected to dihydroartemisinin (DHA), as well as increased chymotrypsin-like activity and decreased accumulation of polyubiquitinated proteins. We thus conclude that the ubiquitin-proteasome pathway, including the 738K variant, play an important role in parasite response to DHA, being the first report of a mutation in a potential DHA drug target enhancing parasite survival and contributing to a significant advance in the understanding the biology of artemisinin resistance.

Novel 2,5-Diketopiperazines with In Vitro Activities against Protozoan Parasites of Tropical Diseases

Malaria, Chagas disease, and leishmaniasis are tropical diseases caused by protozoan parasites of the genera Plasmodium, Trypanosoma and Leishmania, respectively. These diseases constitute a major burden on public health in several regions worldwide, mainly affecting low-income populations in economically poor countries. Severe side effects of currently available drug treatments and the emergence of resistant parasites need to be addressed by the development of novel drug candidates. Natural 2,5-Diketopiperazines (2,5-DKPs) constitute N-heterocyclic secondary metabolites with a wide range of biological activities of medicinal interest. Its structural and physicochemical properties make the 2,5-DKP ring a versatile, peptide-like, and stable pharmacophore attractive for synthetic drug design. In the present work, twenty-three novel synthetic 2,5-DKPs, previously synthesized through the versatile Ugi multicomponent reaction, were assayed for their anti-protozoal activities against P. falciparum, T. cruzi, and L. infantum. Some of the 2,5-DKPs have shown promising activities against the target protozoans, with inhibitory concentrations (IC50) ranging from 5.4 to 9.5 µg/mL. The most active compounds also show low cytotoxicity (CC50), affording selectivity indices ≥ 15. Results allowed for observing a clear relationship between the substitution pattern at the aromatic rings of the 2,5-DKPs and their corresponding anti-Plasmodium activity. Finally, calculated drug-like properties of the compounds revealed points for further structure optimization of promising drug candidates.

Artificial nighttime lighting impacts Plasmodium falciparum mature stage V gametocytes infectivity in Anopheles stephensi

BACKGROUND

Malaria is one of the most important vector-borne diseases of humans with an estimated 241 million cases worldwide in 2020. As an urban and periurban mosquito species, Anopheles stephensi is exposed to artificial human stimuli like light that can alter many aspects of mosquito behaviour, physiology and metabolism. Therefore, fluctuations in the light environment may influence the host, parasite and/or mosquito biology and hence modulate risk for disease transmission. In this study, the effect of artifitial light at night on mosquito infectivity by Plasmodium falciparum during the first hours of blood digestion was tested.

METHODS

A total of three independent standard membrane feeding assays were performed to artificially fed septic and aseptic mosquitoes with P. falciparum infected blood. After blood feeding, females were transferred to incubators with different photoperiod cycles, so digestion occurred under day artificial light or dark. At 7 and 16 days post blood feeding, mosquitoes were dissected for midguts and salivary glands, respectively. Percentage of mosquitoes fed, percentage of prevalence and P. falciparum oocyst intensity between septic and aseptic mosquitoes in the two different photoperiod regimes, were compared using a Kruskal-Wallis test followed by a Dunn´s multiple comparison test .

RESULTS

The exposition of mosquitoes to light after they took an infected blood meal has a negative effect on the successful progression of P. falciparum in the mosquito midgut. Antibiotic treatment significantly incremented the number of oocysts per midgut. Photophase significantly reduced the median oocyst intensity in both septic and aseptic mosquitoes. The percentage of oocyst reduction, understood as the percentage of reduction in the mean oocyst intensity of the parasite in the mosquito midgut between photophase and scotophase, was 51% in the case of aseptic mosquitoes and 80% for septic mosquitoes, both in the photophase condition.

CONCLUSION

Although there are still many gaps in the understanding of parasite-mosquito interactions, these results support the idea that light can, not only, influence mosquito biting behaviour but also parasite success in the mosquito midgut. Hence, light can be considered an interesting additional mosquito-control strategy to reduce mosquito-borne diseases.

Persistence of Anti-SE36 Antibodies Induced by the Malaria Vaccine Candidate BK-SE36/CpG in 5-10-Year-Old Burkinabe Children Naturally Exposed to Malaria

Information on the dynamics and decline/persistence of antibody titres is important in vaccine development. A recent vaccine trial in malaria-exposed, healthy African adults and children living in a malaria hyperendemic and seasonal area (Ouagadougou, Burkina Faso) was the first study in which BK-SE36/CpG was administered to different age groups. In 5- to 10-year-old children, the risk of malaria infection was markedly lower in the BK-SE36/CpG arm compared to the control arm. We report here data on antibody titres measured in this age-group after the high malaria transmission season of 2021 (three years after the first vaccine dose was administered). At Year 3, 83% of children had detectable anti-SE36 total IgG antibodies. Geometric mean antibody titres and the proportion of children with detectable anti-SE36 antibodies were markedly higher in the BK-SE36/CpG arm than the control (rabies) arm. The information obtained in this study will guide investigators on future vaccine/booster schedules for this promising blood-stage malaria vaccine candidate.

Genetic diversity and natural selection of apical membrane antigen-1 (ama-1) in Cameroonian Plasmodium falciparum isolates

Antigenic variation associated with genetic diversity in global Plasmodium falciparum apical membrane antigen-1 (PfAMA-1) is a major impediment to designing an effective malaria vaccine. Here, we report the first study on genetic diversity and natural selection of the Pfama-1 gene in P. falciparum isolates from Cameroon. A total of 328 P. falciparum positive samples collected during 2016 and 2019 from five localities of Cameroon were analysed. The ectodomain coding fragment of Pfama-1 gene was amplified for polymorphism profiling and natural selection analysis. A total of 108 distinct haplotypes were found in 203 P. falciparum isolates with considerable nucleotide diversity (π = 0.016) and haplotype diversity (Hd = 0.976). Most amino acid substitutions detected were scattered in ectodomain-I and few specific mutations viz P145L, K148Q, K462I, L463F, N471K, S482L, E537G, K546R and I547F were seen only in Cameroonian isolates. A tendency of natural selection towards positive diversifying selection was observed (Taj-D = 2.058). Five positively selected codon sites (P145L, S283L, Q308E/K, P330S and I547F) were identified, which overlapped with predicted B-cell epitopes and red blood cell (RBC) binding sites, suggesting their potential implication in host immune pressure and parasite-RBC binding complex modulation. The Cameroonian P. falciparum populations indicated a moderate level of genetic differentiation when compared with global sequences, with few exceptions from Vietnam and Venezuela. Our findings provide baseline data on existing Pfama-1 gene polymorphisms in Cameroonian field isolates, which will be useful information for malaria vaccine design.

Effectiveness of artemether-lumefantrine for treating uncomplicated malaria in low- and high-transmission areas of Ghana

BACKGROUND

Artemisinin-based combination therapy (ACT) has been effective in the supervised treatment of uncomplicated malaria in Ghana. Since ACT usage is primarily unsupervised, this study aimed to determine the effectiveness of artemether-lumefantrine (AL) for treating malaria patients in two transmission settings in Ghana.

METHODS

Eighty-four individuals with uncomplicated Plasmodium falciparum malaria were recruited from Lekma Hospital (LH) in Accra (low-transmission area; N = 28), southern Ghana, and King's Medical Centre (KMC) in Kumbungu (high-transmission area; N = 56), northern Ghana. Participants were followed up for 28 days after unsupervised treatment with AL. The presence of asexual parasites was determined by microscopic examination of Giemsa-stained blood smears. Plasmodium species identification was confirmed using species-specific primers targeting the 18S rRNA gene. Parasite recrudescence or reinfection was determined by genotyping the Pfmsp 1 and Pfmsp 2 genes.

RESULTS

After AL treatment, 3.6% (2/56) of the patients from KMC were parasitaemic on day 3 compared to none from the LH patients. One patient from KMC with delayed parasite clearance on day 3 remained parasite-positive by microscopy on day 7 but was parasite-free by day 14. While none of the patients from LH experienced parasite recurrence during the 28-day follow-up, three and two patients from KMC had recurrent parasitaemia on days 21 and 28, respectively. Percentage reduction in parasite densities from day 1, 2, and 3 for participants from the KMC was 63.2%, 89.5%, and 84.5%. Parasite densities for participants from the LH reduced from 98.2%, 99.8% on day 1, and 2 to 100% on day 3. The 28-day cumulative incidence rate of treatment failure for KMC was 12.8% (95% confidence interval: 1.9-23.7%), while the per-protocol effectiveness of AL in KMC was 89.47%. All recurrent cases were assigned to recrudescence after parasite genotyping by Pfmsp 1 and Pfmsp 2.

CONCLUSION

While AL is efficacious in treating uncomplicated malaria in Ghana, when taken under unsupervised conditions, it showed an 89.4% PCR-corrected cure rate in northern Ghana, which is slightly below the WHO-defined threshold.

Structural and functional characterization of 6-phosphogluconate dehydrogenase in Plasmodium falciparum (3D7) and identification of its potent inhibitors

The malarial parasite Plasmodium falciparum predominantly causes severe malaria and deaths worldwide. Moreover, resistance developed by P. falciparum to frontline drugs in recent years has markedly increased malaria-related deaths in South Asian Countries. Ribulose 5-phosphate and NADPH synthesized by Pentose Phosphate Pathway (PPP) act as a direct precursor for nucleotide synthesis and P. falciparum survival during oxidative challenges in the intra-erythrocytic growth phase . In the present study, we have elucidated the structure and functional characteristics of 6-phosphogluconate dehydrogenase (6PGD) in P. falciparum and have identified potent hits against 6PGD by pharmacophore-based virtual screening with ZINC and ChemBridge databases. Molecular docking and Molecular dynamics simulation, binding free energies (MMGBSA & MMPBSA), and Density Functional Theory (DFT) calculations were integratively employed to validate and prioritize the most potential hits. The 6PGD structure was found to have an open and closed conformation during MD simulation. The apo form of 6PGD was found to be in closed conformation, while a open conformation attributed to facilitating binding of cofactor. It was also inferred from the conformational analysis that the small domain of 6PGD has a high influence in altering the conformation that may aid in open/closed conformation of 6PGD. The top three hits identified using pharmacophore hypotheses were ChemBridge_11084819, ChemBridge_80178394, and ChemBridge_17912340. Though all three hits scored a high glide score, MMGBSA, and favorable ADMET properties, ChemBridge_11084819 and ChemBrdige_17912340 showed higher stability and binding free energy. Moreover, these hits also featured stable H-bond interactions with the active loop of 6PGD with binding free energy comparable to substrate-bound complex. Therefore, the ChemBridge_11084819 and ChemBridge_17912340 moieties demonstrate to have high therapeutic potential against 6PGD in P. falciparum.Communicated by Ramaswamy H. Sarma.

The problem of antimalarial resistance and its implications for drug discovery

INTRODUCTION

Malaria remains a devastating infectious disease with hundreds of thousands of casualties each year. Antimalarial drug resistance has been a threat to malaria control and elimination for many decades and is still of concern today. Despite the continued effectiveness of current first-line treatments, namely artemisinin-based combination therapies, the emergence of drug-resistant parasites in Southeast Asia and even more alarmingly the occurrence of resistance mutations in Africa is of great concern and requires immediate attention.

AREAS COVERED

A comprehensive overview of the mechanisms underlying the acquisition of drug resistance in Plasmodium falciparum is given. Understanding these processes provides valuable insights that can be harnessed for the development and selection of novel antimalarials with reduced resistance potential. Additionally, strategies to mitigate resistance to antimalarial compounds on the short term by using approved drugs are discussed.

EXPERT OPINION

While employing strategies that utilize already approved drugs may offer a prompt and cost-effective approach to counter antimalarial drug resistance, it is crucial to recognize that only continuous efforts into the development of novel antimalarial drugs can ensure the successful treatment of malaria in the future. Incorporating resistance propensity assessment during this developmental process will increase the likelihood of effective and enduring malaria treatments.