Melatonin as a Circadian Marker for Plasmodium Rhythms.

Plasmodium, a digenetic parasite, requires a host and a vector for its life cycle completion. Most Plasmodium species display circadian rhythmicity during their intraerythrocytic cycle within the host, aiding in immune evasion. This rhythmicity, however, diminishes in in vitro cultures, highlighting the importance of host-derived signals for synchronizing the parasite's asexual cycle. Studies indicate a species-specific internal clock in Plasmodium, dependent on these host signals. Melatonin, a hormone the pineal gland produces under circadian regulation, impacts various physiological functions and is extensively reviewed as the primary circadian marker affecting parasite rhythms. Research suggests that melatonin facilitates synchronization through the PLC-IP3 signaling pathway, activating phospholipase C, which triggers intracellular calcium release and gene expression modulation. This evidence strongly supports the role of melatonin as a key circadian marker for parasite synchronization, presenting new possibilities for targeting the melatonin pathway when developing novel therapeutic approaches.

A geometrical theory of gliding motility based on cell shape and surface flow.

Gliding motility proceeds with little changes in cell shape and often results from actively driven surface flows of adhesins binding to the extracellular environment. It allows for fast movement over surfaces or through tissue, especially for the eukaryotic parasites from the phylum apicomplexa, which includes the causative agents of the widespread diseases malaria and toxoplasmosis. We have developed a fully three-dimensional active particle theory which connects the self-organized, actively driven surface flow over a fixed cell shape to the resulting global motility patterns. Our analytical solutions and numerical simulations show that straight motion without rotation is unstable for simple shapes and that straight cell shapes tend to lead to pure rotations. This suggests that the curved shapes of Plasmodium sporozoites and Toxoplasma tachyzoites are evolutionary adaptations to avoid rotations without translation. Gliding motility is also used by certain myxo- or flavobacteria, which predominantly move on flat external surfaces and with higher control of cell surface flow through internal tracks. We extend our theory for these cases. We again find a competition between rotation and translation and predict the effect of internal track geometry on overall forward speed. While specific mechanisms might vary across species, in general, our geometrical theory predicts and explains the rotational, circular, and helical trajectories which are commonly observed for microgliders. Our theory could also be used to design synthetic microgliders.

Allorecognition behaviors in Myxomycetes respond to intraspecies factors.

Myxomycetes are multinucleate unicellular organisms. They form a Plasmodium that moves by protoplasmic flow and prey on microorganisms. When encountering intraspecifics, the plasmodium has the capacity for 'fusion', actively approaching and fusing its cells, or 'avoidance', altering its direction to avoid the other individual. This is an allorecognition ability. However, it remains unclear whether the range of allorecognition extends to other species, and its ecological significance is also obscure. Here, we conducted a quantitative evaluation of contact responses from closely related species of plasmodium to clarify the range of allorecognition behaviors in Myxomycetes. Behavioral assays demonstrated that allorecognition behaviors are specifically observed within individuals of the same species, indicating that these behaviors are a phenomenon unique to intraspecies interactions. Myxomycetes allorecognition is an extremely narrow and inward-focused behavior, suggesting a highly specialized mechanism.

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

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

Tripartite interactions between viruses, parasites, and mosquitoes.

Mosquito-borne diseases have a major impact on global human health. Biological agents that colonize the mosquito vector are increasingly explored as an intervention strategy to prevent vector-borne disease transmission. For instance, the release of mosquitoes carrying the endosymbiotic bacterium Wolbachia effectively reduced dengue virus incidence and disease. Insect-specific viruses are likewise considered as biocontrol agents against vector-borne diseases. While most studies focused on insect-specific viruses as an intervention against arthropod-borne viruses, we here consider whether mosquito-specific viruses may affect the transmission of the malaria-causing Plasmodium parasite by Anopheles mosquitoes. Although there is no direct experimental evidence addressing this question, we found that viral infections in dipteran insects activate some of the immune pathways that are antiparasitic in Anopheles. These findings suggest that indirect virus-parasite interactions could occur and that insect-specific viruses may modulate malaria transmission. Tripartite interactions between viruses, parasites, and Anopheles mosquitoes thus merit further investigation.

Hepatocytes and the art of killing Plasmodium softly.

The Plasmodium parasites that cause malaria undergo asymptomatic development in the parenchymal cells of the liver, the hepatocytes, prior to infecting erythrocytes and causing clinical disease. Traditionally, hepatocytes have been perceived as passive bystanders that allow hepatotropic pathogens such as Plasmodium to develop relatively unchallenged. However, now there is emerging evidence suggesting that hepatocytes can mount robust cell-autonomous immune responses that target Plasmodium, limiting its progression to the blood and reducing the incidence and severity of clinical malaria. Here we discuss our current understanding of hepatocyte cell-intrinsic immune responses that target Plasmodium and how these pathways impact malaria.

The molecular mechanisms driving Plasmodium cell division.

Malaria, a vector borne disease, is a major global health and socioeconomic problem caused by the apicomplexan protozoan parasite Plasmodium. The parasite alternates between mosquito vector and vertebrate host, with meiosis in the mosquito and proliferative mitotic cell division in both hosts. In the canonical eukaryotic model, cell division is either by open or closed mitosis and karyokinesis is followed by cytokinesis; whereas in Plasmodium closed mitosis is not directly accompanied by concomitant cell division. Key molecular players and regulatory mechanisms of this process have been identified, but the pivotal role of certain protein complexes and the post-translational modifications that modulate their actions are still to be deciphered. Here, we discuss recent evidence for the function of known proteins in Plasmodium cell division and processes that are potential novel targets for therapeutic intervention. We also identify key questions to open new and exciting research to understand divergent Plasmodium cell division.

Changes in hypothalamic-pituitary-adrenal axis function, immunity, and glucose during acute Plasmodium relictum infection in house sparrows (Passer domesticus).

Hosts of the same species vary in physiological responses to the same parasite, and some groups of individuals can disproportionately affect disease dynamics; however, the underlying pathophysiology of host-parasite interactions is poorly understood in wildlife. We tested the hypothesis that the hypothalamic-pituitary-adrenal (HPA) axis mediates host resistance and tolerance to avian malaria during the acute phase of infection by evaluating whether individual variation in circulating glucocorticoids predicted resistance to avian malaria in a songbird. We experimentally inoculated wild-caught house sparrows (Passer domesticus) with naturally sourced Plasmodium relictum and quantified baseline and restraint-induced circulating corticosterone, negative feedback ability, cellular and humoral immune function, and baseline and restraint-induced glycemia, prior to and during acute malaria infection. During peak parasitemia, we also evaluated the expression of several liver cytokines that are established pathological hallmarks of malaria in mammals: two pro-inflammatory (IFN-γ and TNF-α) and two anti-inflammatory (IL-10 and TGF-ß). Although most of the host metrics we evaluated were not correlated with host resistance or tolerance to avian malaria, this experiment revealed novel relationships between malarial parasites and the avian immune system that further our understanding of the pathology of malaria infection in birds. Specifically, we found that: (1) TNF-α liver expression was positively correlated with parasitemia; (2) sparrows exhibited an anti-inflammatory profile during malaria infection; and (3) IFN-γ and circulating glucose were associated with several immune parameters, but only in infected sparrows. We also found that, during the acute phase of infection, sparrows increased the strength of corticosterone negative feedback at the level of the pituitary. In the context of our results, we discuss future methodological considerations and aspects of host physiology that may confer resistance to avian malaria, which can help inform conservation and rehabilitation strategies for avifauna at risk.

How colonization bottlenecks, tissue niches, and transmission strategies shape protozoan infections.

Protozoan pathogens such as Plasmodium spp., Leishmania spp., Toxoplasma gondii, and Trypanosoma spp. are often associated with high-mortality, acute and chronic diseases of global health concern. For transmission and immune evasion, protozoans have evolved diverse strategies to interact with a range of host tissue environments. These interactions are linked to disease pathology, yet our understanding of the association between parasite colonization and host homeostatic disruption is limited. Recently developed techniques for cellular barcoding have the potential to uncover the biology regulating parasite transmission, dissemination, and the stability of infection. Understanding bottlenecks to infection and the in vivo tissue niches that facilitate chronic infection and spread has the potential to reveal new aspects of parasite biology.

A Plasmodium membrane receptor platform integrates cues for egress and invasion in blood forms and activation of transmission stages.

Critical events in the life cycle of malaria-causing parasites depend on cyclic guanosine monophosphate homeostasis by guanylyl cyclases (GCs) and phosphodiesterases, including merozoite egress or invasion of erythrocytes and gametocyte activation. These processes rely on a single GCα, but in the absence of known signaling receptors, how this pathway integrates distinct triggers is unknown. We show that temperature-dependent epistatic interactions between phosphodiesterases counterbalance GCα basal activity preventing gametocyte activation before mosquito blood feed. GCα interacts with two multipass membrane cofactors in schizonts and gametocytes: UGO (unique GC organizer) and SLF (signaling linking factor). While SLF regulates GCα basal activity, UGO is essential for GCα up-regulation in response to natural signals inducing merozoite egress and gametocyte activation. This work identifies a GC membrane receptor platform that senses signals triggering processes specific to an intracellular parasitic lifestyle, including host cell egress and invasion to ensure intraerythrocytic amplification and transmission to mosquitoes.

Same, same but different: Exploring Plasmodium cell division during liver stage development.

Plasmodium parasites have a complex life cycle alternating between a mosquito and a vertebrate host. Following the bite of an Anopheles female mosquito, Plasmodium sporozoites are transmitted from the skin to the liver; their first place of replication within the host. Successfully invaded sporozoites undergo a massive replication and growth involving asynchronous DNA replication and division that results in the generation of tens of thousands or even hundreds of thousands of merozoites depending on the Plasmodium species. The generation of a high number of daughter parasites requires biogenesis and segregation of organelles to finally reach a relatively synchronous cytokinesis event. At the end of liver stage (LS) development, merozoites are packed into merosomes and released into the bloodstream. They are then liberated and infect red blood cells to again produce merozoites by schizogony for the erythrocytic stage of the life cycle. Although parasite LS and asexual blood stage (ABS) differ in many respects, important similarities exist between the two. This review focuses on the cell division of Plasmodium parasite LS in comparison with other life cycle stages especially the parasite blood stage.

The microbiota, the malarial parasite, and the mosquito [MMM] - A three-sided relationship.

The mosquito gut microbiota is vital to the proper functioning of the host organism. Mosquitoes may benefit from this microbiota in their guts because it promotes factors including blood digestion, fecundity, metamorphosis, and living habitat and inhibits malarial parasites (Plasmodium) growth or transmission. In this overview, we analyzed how mosquitoes acquire their gut microbiota, characterized those bacteria, and discussed the functions they provide. We also investigated the effects of microbiota on malaria vectors, with a focus on the mosquito species Anopheles, as well as the relationship between microbiota and Plasmodium, the aspects in which microbiota influences Plasmodium via immune response, metabolism, and redox mechanisms, and the strategies in which gut bacteria affect the life cycle of malaria vectors and provide the ability to resist insecticides. This article explores the difficulties in studying triadic interactions, such as the interplay between Mosquitoes, Malarial parasite, and the Microbiota that dwell in the mosquitoes' guts, and need additional research for a better understanding of these multiple connections to implement an exact vector control strategies using Gut microbiota in malaria control.

An evaluation of fusion partner proteins for paratransgenesis in Asaia bogorensis.

Mosquitoes transmit many pathogens responsible for human diseases, such as malaria which is caused by parasites in the genus Plasmodium. Current strategies to control vector-transmitted diseases are increasingly undermined by mosquito and pathogen resistance, so additional methods of control are required. Paratransgenesis is a method whereby symbiotic bacteria are genetically modified to affect the mosquito's phenotype by engineering them to deliver effector molecules into the midgut to kill parasites. One paratransgenesis candidate is Asaia bogorensis, a Gram-negative bacterium colonizing the midgut, ovaries, and salivary glands of Anopheles sp. mosquitoes. Previously, engineered Asaia strains using native signals to drive the release of the antimicrobial peptide, scorpine, fused to alkaline phosphatase were successful in significantly suppressing the number of oocysts formed after a blood meal containing P. berghei. However, these strains saw high fitness costs associated with the production of the recombinant protein. Here, we report evaluation of five different partner proteins fused to scorpine that were evaluated for effects on the growth and fitness of the transgenic bacteria. Three of the new partner proteins resulted in significant levels of protein released from the Asaia bacterium while also significantly reducing the prevalence of mosquitoes infected with P. berghei. Two partners performed as well as the previously tested Asaia strain that used alkaline phosphatase in the fitness analyses, but neither exceeded it. It may be that there is a maximum level of fitness and parasite inhibition that can be achieved with scorpine being driven constitutively, and that use of a Plasmodium specific effector molecule in place of scorpine would help to mitigate the stress on the symbionts.

Transgenic Anopheles mosquitoes expressing human PAI-1 impair malaria transmission.

In mammals, the serine protease plasmin degrades extracellular proteins during blood clot removal, tissue remodeling, and cell migration. The zymogen plasminogen is activated into plasmin by two serine proteases: tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), a process regulated by plasminogen activator inhibitor 1 (PAI-1), a serine protease inhibitor that specifically inhibits tPA and uPA. Plasmodium gametes and sporozoites use tPA and uPA to activate plasminogen and parasite-bound plasmin degrades extracellular matrices, facilitating parasite motility in the mosquito and the mammalian host. Furthermore, inhibition of plasminogen activation by PAI-1 strongly blocks infection in both hosts. To block parasite utilization of plasmin, we engineered Anopheles stephensi transgenic mosquitoes constitutively secreting human PAI-1 (huPAI-1) in the midgut lumen, in the saliva, or both. Mosquitoes expressing huPAI-1 strongly reduced rodent and human Plasmodium parasite transmission to mosquitoes, showing that co-opting plasmin for mosquito infection is a conserved mechanism among Plasmodium species. huPAI-1 expression in saliva induced salivary gland deformation which affects sporozoite invasion and P. berghei transmission to mice, resulting in significant levels of protection from malaria. Targeting the interaction of malaria parasites with the fibrinolytic system using genetically engineered mosquitoes could be developed as an intervention to control malaria transmission.

Exo-erythrocytic development of Plasmodium matutinum (lineage pLINN1) in a naturally infected roadkill fieldfare Turdus pilaris.

BACKGROUND: Species of Plasmodium (Haemosporida, Plasmodiidae) are remarkably diverse haemoparasites. Information on genetic diversity of avian malaria pathogens has been accumulating rapidly, however exo-erythrocytic development of these organisms remains insufficiently addressed. This is unfortunate because, contrary to Plasmodium species parasitizing mammals, the avian malaria parasites undergo several cycles of exo-erythrocytic development, often resulting in damage of various organs. Insufficient knowledge on the exo-erythrocytic development in most described Plasmodium species precludes the understanding of mechanisms of virulence during avian malaria. This study extends information on the exo-erythrocytic development of bird malaria parasites. METHODS: A roadkill fieldfare (Turdus pilaris) was sampled in Switzerland and examined using pathologic, cytologic, histologic, molecular and microbiologic methods. Avian malaria was diagnosed, and erythrocytic and exo-erythrocytic stages of the parasite were identified using morphologic characteristics and barcode DNA sequences of the cytochrome b gene. The species-specific characteristics were described, illustrated, and pathologic changes were reported. RESULTS: An infection with Plasmodium matutinum lineage pLINN1 was detected. Parasitaemia was relatively low (0.3%), with all erythrocytic stages (trophozoites, meronts and gametocytes) present in blood films. Most growing erythrocytic meronts were markedly vacuolated, which is a species-specific feature of this parasite's development. Phanerozoites at different stages of maturation were seen in leukocytes, macrophages, and capillary endothelial cells in most organs examined; they were particularly numerous in the brain. Like the erythrocytic meronts, growing phanerozoites were markedly vacuolated. Conspicuous exo-erythrocytic development and maturation in leucocytes suggests that this fieldfare was not adapted to the infection and the parasite was capable to escape from cellular immunity. CONCLUSIONS: This is the first report of exo-erythrocytic development of the malaria parasite lineage pLINN1 during single infection and the first report of this lineage in the fieldfare. The findings of multiple phanerozoites in brain, skeletal muscle, and eye tissue in combination with signs of vascular blockage and thrombus formation strongly suggest an impaired vision and neuromuscular responsiveness as cause of the unexpected collision with a slowly moving car. Further studies on exo-erythrocytic stages of haemosporidian parasites are pivotal to understand the true level of populational damage of avian malaria in wild birds.

Expansion microscopy of Plasmodium gametocytes reveals the molecular architecture of a bipartite microtubule organisation centre coordinating mitosis with axoneme assembly.

Transmission of malaria-causing parasites to mosquitoes relies on the production of gametocyte stages and their development into gametes. These stages display various microtubule cytoskeletons and the architecture of the corresponding microtubule organisation centres (MTOC) remains elusive. Combining ultrastructure expansion microscopy (U-ExM) with bulk proteome labelling, we first reconstructed in 3D the subpellicular microtubule network which confers cell rigidity to Plasmodium falciparum gametocytes. Upon activation, as the microgametocyte undergoes three rounds of endomitosis, it also assembles axonemes to form eight flagellated microgametes. U-ExM combined with Pan-ExM further revealed the molecular architecture of the bipartite MTOC coordinating mitosis with axoneme formation. This MTOC spans the nuclear membrane linking cytoplasmic basal bodies to intranuclear bodies by proteinaceous filaments. In P. berghei, the eight basal bodies are concomitantly de novo assembled in a SAS6- and SAS4-dependent manner from a deuterosome-like structure, where centrin, γ-tubulin, SAS4 and SAS6 form distinct subdomains. Basal bodies display a fusion of the proximal and central cores where centrin and SAS6 are surrounded by a SAS4-toroid in the lumen of the microtubule wall. Sequential nucleation of axonemes and mitotic spindles is associated with a dynamic movement of γ-tubulin from the basal bodies to the intranuclear bodies. This dynamic architecture relies on two non-canonical regulators, the calcium-dependent protein kinase 4 and the serine/arginine-protein kinase 1. Altogether, these results provide insights into the molecular organisation of a bipartite MTOC that may reflect a functional transition of a basal body to coordinate axoneme assembly with mitosis.

Evolutionary Insights into the Microneme-Secreted, Chitinase-Containing High-Molecular-Weight Protein Complexes Involved in Plasmodium Invasion of the Mosquito Midgut.

While general mechanisms by which Plasmodium ookinetes invade the mosquito midgut have been studied, details regarding the interface of the ookinete, specifically its barriers to invasion, such as the proteolytic milieu, the chitin-containing, protein cross-linked peritrophic matrix, and the midgut epithelium, remain to be understood. Here, we review our knowledge of Plasmodium chitinases and the mechanisms by which they mediate ookinetes crossing the peritrophic matrix. The integration of new genomic insights into previous findings advances our understanding of Plasmodium evolution. Recently obtained Plasmodium species genomic data enable identification of the conserved residues in the experimentally demonstrated hetero-multimeric, high-molecular-weight complex comprised of a short chitinase covalently linked to binding partners, von Willebrand factor A domain-related protein (WARP) and secreted ookinete adhesive protein (SOAP). Artificial intelligence-based high-resolution structural modeling using the DeepMind AlphaFold algorithm yielded highly informative three-dimensional structures and insights into how short chitinases, WARP, and SOAP may interact at the atomic level to form the ookinete-secreted peritrophic matrix invasion complex. Elucidating the significance of the divergence of ookinete-secreted micronemal proteins among Plasmodium species may lead to a better understanding of the ookinete invasion machinery and the coevolution of Plasmodium-mosquito interactions.

Malaria infection and anemia status in under-five children from Southern Tanzania where seasonal malaria chemoprevention is being implemented.

BACKGROUND: Malaria and anemia remain major public health challenges in Tanzania. Household socioeconomic factors are known to influence these conditions. However, it is not clear how these factors influence malaria transmission and anemia in Masasi and Nanyumbu Districts. This study presents findings on malaria and anemia situation in under-five children and its influencing socioeconomic factors in Masasi and Nanyumbu Districts, surveyed as part of an ongoing seasonal malaria chemoprevention operational study. METHODS: A community-based cross-sectional survey was conducted between August and September 2020. Finger-prick blood samples collected from children aged 3-59 months were used to test for malaria infection using malaria rapid diagnostic test (mRDT), thick smears for determination of asexual and sexual parasitemia, and thin smear for parasite speciation. Hemoglobin concentration was measured using a HemoCue spectrophotometer. A structured questionnaire was used to collect household socioeconomic information from parents/caregivers of screened children. The prevalence of malaria was the primary outcome. Chi-square tests, t-tests, and logistic regression models were used appropriately. RESULTS: Overall mRDT-based malaria prevalence was 15.9% (373/2340), and was significantly higher in Nanyumbu (23.7% (167/705) than Masasi District (12.6% (206/1635), p<0.001. Location (Nanyumbu), no formal education, household number of people, household number of under-fives, not having a bed net, thatched roof, open/partially open eave, sand/soil floor, and low socioeconomic status were major risks for malaria infection. Some 53.9% (1196/2218) children had anemia, and the majority were in Nanyumbu (63.5% (458/705), p<0.001. Location (Nanyumbu), mRDT positive, not owning a bed net, not sleeping under bed net, open/partially open eave, thatched window, sex of the child, and age of the child were major risk factors for anemia. CONCLUSION: Prevalence of malaria and anemia was high and was strongly associated with household socioeconomic factors. Improving household socioeconomic status is expected to reduce the prevalence of the conditions in the area.

The State of Art of Extracellular Traps in Protozoan Infections (Review).

Protozoan parasite infection causes severe diseases in humans and animals, leading to tremendous economic and medical pressure. Natural immunity is the first line of defence against parasitic infection. Currently, the role of natural host immunity in combatting parasitic infection is unclear, so further research on natural host immunity against parasites will provide a theoretical basis for the prevention and treatment of related parasitic diseases. Extracellular traps (ETs) are an important natural mechanism of immunity involving resistance to pathogens. When immune cells such as neutrophils and macrophages are stimulated by external pathogens, they release a fibrous network structure, consisting mainly of DNA and protein, that can capture and kill a variety of extracellular pathogenic microorganisms. In this review, we discuss the relevant recently reported data on ET formation induced by protozoan parasite infection, including the molecular mechanisms involved, and discuss the role of ETs in the occurrence and development of parasitic diseases.

Extracellular vesicles in malaria: an agglomeration of two decades of research.

Malaria is a complex parasitic disease, caused by Plasmodium spp. More than a century after the discovery of malaria parasites, this disease continues to pose a global public health problem and the pathogenesis of the severe forms of malaria remains incompletely understood. Extracellular vesicles (EVs), including exosomes and microvesicles, have been increasingly researched in the field of malaria in a bid to fill these knowledge gaps. EVs released from Plasmodium-infected red blood cells and other host cells during malaria infection are now believed to play key roles in disease pathogenesis and are suggested as vital components of the biology of Plasmodium spp. Malaria-derived EVs have been identified as potential disease biomarkers and therapeutic tools. In this review, key findings of malaria EV studies over the last 20 years are summarized and critically analysed. Outstanding areas of research into EV biology are identified. Unexplored EV research foci for the future that will contribute to consolidating the potential for EVs as agents in malaria prevention and control are proposed.