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The pathology of malaria is caused by infection of red blood cells with unicellular Plasmodium parasites. During blood-stage development, the parasite replicates within a membrane-bound parasitophorous vacuole. A central nexus for host–parasite interactions, this unique parasite shelter functions in nutrient acquisition, subcompartmentalization and the export of virulence factors, making its functional molecules attractive targets for the development of novel intervention strategies to combat the devastating impact of malaria. In this Review, we explore the origin, development, molecular composition and functions of the parasitophorous vacuole of Plasmodium blood stages. We also discuss the relevance of the malaria parasite’s intravacuolar lifestyle for successful erythrocyte infection and provide perspectives for future research directions in parasitophorous vacuole biology. During intraerythrocytic development, malaria parasites replicate within a membrane-bound parasitophorous vacuole. In this Review, Matz, Beck and Blackman explore the origin, development, molecular composition and functions of the parasitophorous vacuole during blood-stage development. They also discuss the relevance of the malaria parasite’s intravacuolar lifestyle for successful erythrocyte infection and provide perspectives for future research directions.

Malaria is a disease affecting hundreds of millions of people across the world, mainly in developing countries and especially in sub-Saharan Africa. It is the cause of hundreds of thousands of deaths each year and there is an ever-present need to identify and develop effective new therapies to tackle the disease and overcome increasing drug resistance. Here, we extend a previous study in which a number of partners collaborated to develop a consensus in silico model that can be used to identify novel molecules that may have antimalarial properties. The performance of machine learning methods generally improves with the number of data points available for training. One practical challenge in building large training sets is that the data are often proprietary and cannot be straightforwardly integrated. Here, this was addressed by sharing QSAR models, each built on a private data set. We describe the development of an open-source software platform for creating such models, a comprehensive evaluation of methods to create a single consensus model and a web platform called MAIP available at https://www.ebi.ac.uk/chembl/maip/. MAIP is freely available for the wider community to make large-scale predictions of potential malaria inhibiting compounds. This project also highlights some of the practical challenges in reproducing published computational methods and the opportunities that open-source software can offer to the community.

Fluorescence lifetime imaging (FLIM) measures the characteristic time that a molecule remains in an excited state prior to emitting a photon and returning to the ground state. It is a state-of-the-art and noninvasive technique that has the potential to obtain signature physiological information during malaria blood-stage infection. The use of autofluorescence signals from intrinsic fluorophores obviates the need to tag the cells with synthetic molecules or to modify their gene expression. Furthermore, it permits time-lapse interrogation of the changes that occur from invasion to the point when the parasite takes over the host for its own survival mechanisms, as well as changes in the health of the parasite due to extrinsically applied metabolic disruptors. In this chapter, we present a protocol to investigate the autofluorescence lifetime signals of both normal red blood cells (RBC) and P. falciparum-infected RBCs. The data shared with this protocol reveals that there is a significant overall increase in autofluorescence lifetime in infected erythrocytes compared to the healthy uninfected ones. We include a metabolic experiment that confirms that the signals obtained from this imaging technique are key metabolites in energetics of the parasites. Furthermore, facilitating these protocols makes it possible to identify infected RBC based on FLIM signals alone, which presents a huge potential for the study of energetic effects of antimalarials and fast, noninvasive diagnosing.

Successful herbicides, like drugs, have physico-chemical properties that usually fall within certain limits. A recent analysis of 334 herbicides showed similar properties to the ‘rule of five’ for human orally-delivered drugs, but herbicides diverged from this for proton donors, partition coefficients and molecular weight. To refine rules for herbicides, we exploited the close evolutionary relationship between P. falciparum and plants by screening the Malaria Box, a 400-compound library composed of novel chemical scaffolds with activity against blood stage malaria parasite Plasmodium falciparum. A high proportion (52 of 400) were herbicidal to Arabidopsis thaliana on agar plates. Thirty-nine of these 52 herbicidal compounds were tested on soil and 16 compounds were herbicidal. These data were used to predict whether a herbicidal hit found on agar will work on soil-grown plants. The physico-chemical parameters were weighted to logP and formal charge and used to generate weighted scores to a large chemical library of liver-stage effective antimalarial leads. Of the six top-scoring compounds, one had a potency comparable to commercial herbicides. This novel compound MMV1206386 had no close structural matches among commercial herbicides. Physiological profiling suggested that MMV1206386 has a new mode of action and overall demonstrates how weighted rules can help during herbicide discovery programs.

Malaria is a disease affecting hundreds of millions of people across the world, mainly in developing countries and especially in Sub-Saharan Africa. It is the cause of hundreds of thousands of deaths each year and there is an ever-present need to identify and develop effective new therapies to tackle the disease and overcome increasing drug resistance. Here, we extend a previous study in which a number of partners collaborated to develop a consensus in silico model that can be used to identify novel molecules that may have antimalarial properties. The performance of machine learning methods generally improves with the number of data points available for training. One practical challenge in building large training sets is that the data is often proprietary and cannot be straightforwardly integrated. Here, this was addressed by sharing QSAR models, each built on a private data set. We describe the development of an open-source software platform for creating such models, a comprehensive evaluation of methods to create a single consensus model and a web platform called MAIP available at https://www.ebi.ac.uk/chembl/maip/. MAIP is freely available for the wider community to make large-scale predictions of potential malaria inhibiting compounds. This project also highlights some of the practical challenges in reproducing published computational methods and the opportunities that open source software can offer to the community.

Introduction: As the quest for an effective blood stage malaria vaccine continues, there is increasing reliance on the use of controlled human malaria infections (CHMI) in non-endemic settings to test vaccine efficacy at the earliest possible time. This is seen as a way to accelerate vaccine research and quickly eliminate candidates with poor efficacy.Areas covered: The data from these studies need to be carefully examined and interpreted in light of the very different roles that antibody and cellular immunity play in protection and within the context of the distinct clinical sensitivities of volunteers living in malaria-non-endemic countries compared to those living in endemic countries. With current strategies, it is likely that vaccines with protective immunological ‘signatures’ will be missed and potentially good candidates discarded.Expert commentary: Efficacy data from early phase vaccine trials in non-endemic countries should not be used to decide whether or not to proceed to vaccine trials...

We consider a mathematical model for malaria involving, susceptible red blood cells (RBCs), latent infected red blood cells (RBCs), active IRBCs, intracellular parasites, extracellular parasites and effector cells. We extend the model to include effect of treatment on the prognosis of malaria. One of the questions addressed in our study is: what range of the parameter, [Formula: see text] which denotes the number of intracellular parasites released from a naturally dying activated infected red blood cell can lead to malaria pathogenesis? Sensitivity analysis revealed that poor parametric estimation can lead to wrong disease prognosis, and consequently to over or under-prescription of treatment drugs. In malaria endemic areas where the parasite is developing resistance to the drugs, this can limit options of treatment drugs. We recommend that the administration of malaria treatment drugs should be done under supervision as is the case for TB to ensure complete adherence to treatment and reduce the emergence of malaria drug resistant strains. Secondly, we recommend that individuals with malaria or showing symptoms of the disease should be tested for other chronic infections which could complicate the treatment of malaria.

Malaria remains a major burden world-wide, but the disease-causing parasites from the genus Plasmodium are difficult to study in vitro. Owing to the small size of the parasites, subcellular imaging poses a major challenge and the use of super-resolution techniques has been hindered by the parasites’ sensitivity to light. This is particularly apparent during the blood-stage of the Plasmodium life cycle, which presents an important target for drug research. The iron-rich food vacuole of the parasite undergoes disintegration when illuminated with high-power lasers such as those required for high resolution in Stimulated Emission Depletion (STED) microscopy. This causes major damage to the sample precluding the use of this super-resolution technique. Here we present guided STED, a novel adaptive illumination (AI) STED approach, which takes advantage of the highly-reflective nature of the iron deposit in the cell to identify the most light-sensitive parts of the sample. Specifically in these parts, the high-power STED laser is deactivated automatically to prevent local damage. Guided STED nanoscopy finally allows super-resolution imaging of the whole Plasmodium life cycle, enabling multicolour imaging of blood-stage malaria parasites with resolutions down to 35 nm without sample destruction.

The blood stage of the malaria parasite life cycle is responsible for all the clinical symptoms of malaria. During the blood stage, Plasmodium merozoites invade and multiply within host red blood cells (RBCs). Here, we review the progress made, challenges faced, and new strategies available for the development of blood stage malaria vaccines. We discuss our current understanding of immune responses against blood stages and the status of clinical development of various blood stage malaria vaccine candidates. We then discuss possible paths forward to develop effective blood stage malaria vaccines. This includes a discussion of protective immune mechanisms that can be elicited to target blood stage parasites, novel delivery systems, immunoassays and animal models to optimize vaccine candidates in preclinical studies, and use of challenge models to get an early readout of vaccine efficacy.

There have been significant decreases in malaria mortality and morbidity in the last 10-15 years, and the most advanced pre-erythrocytic malaria vaccine, RTS,S, received a positive opinion from European regulators in July 2015. However, no blood-stage vaccine has reached a phase III trial. The first part of this review summarizes the pros and cons of various assays and models that have been and will be used to predict the efficacy of blood-stage vaccines. In the second part, blood-stage vaccine candidates that showed some efficacy in human clinical trials or controlled human malaria infection models are discussed. Then, candidates under clinical investigation are described in the third part, and other novel candidates and strategies are reviewed in the last part.

Malaria is one of the most dangerous diseases that threatens people’s lives around the world. In this paper, we study a reaction-diffusion model for the within-host dynamics of malaria infection with an antibody immune response. The model is given by a system of partial differential equations (PDEs) to describe the blood-stage of malaria life cycle. It addresses the interactions between uninfected red blood cells, antibodies, and three types of infected red blood cells, namely ring-infected red blood cells, trophozoite-infected red blood cells and schizont-infected red blood cells. Moreover, the model contains a parameter to measure the efficacy of isoleucine starvation and its effect on the growth of malaria parasites. We show the basic properties of the model. We compute all equilibria and derive the thresholds from the conditions of existence of malaria equilibrium points. We prove the global stability of all equilibrium points based on choosing suitable Lyapunov functionals. We use the characteristic equations to verify the local instability of equilibrium points. We finally execute numerical simulations to validate the theoretical results and highlight some important observations. The results indicate that isoleucine starvation can have a critical impact on the stability of equilibrium points. When the efficacy of isoleucine starvation is high, it switches the system from the infection state to the malaria-free state. The presence of an antibody immune response does not lead to the elimination of malaria infection, but it suppresses the growth of malaria parasites and increases the amount of healthy red blood cells.

An efficacious malaria vaccine is necessary to advance the current control measures towards malaria elimination. To-date, only RTS,S/AS01, a leading pre-erythrocytic stage vaccine completed phase 3 trials, but with an efficacy of 28-36% in children, and 18-26% in infants, that waned over time. Blood-stage malaria vaccines protect against disease, and are considered effective targets for the logical design of next generation vaccines to improve the RTS,S field efficacy. Therefore, novel blood-stage vaccine candidate discovery efforts are critical, albeit with several challenges including, high polymorphisms in vaccine antigens, poor understanding of targets of naturally protective immunity, and difficulties in the expression of high AT-rich plasmodial proteins. Areas covered: PubMed ( www.ncbi.nlm.nih.gov/pubmed ) was searched to review the progress and future prospects of malaria vaccine research and development. We focused on post-genome vaccine candidate discovery, malaria vaccine development, sequence diversity, pre-clinical and clinical trials. Expert commentary: Post-genome high-throughput technologies using wheat germ cell-free protein synthesis technology and immuno-profiling with sera from malaria patients with clearly defined outcomes are highlighted to overcome current challenges of malaria vaccine candidate discovery.

The development of new antimalarial therapies is essential, and lowering the barrier of entry for the screening and discovery of new lead compound classes can spur drug development at organizations that may not have large compound screening libraries or resources to conduct high-throughput screens. Machine learning models have been long established to be more robust and have a larger domain of applicability with larger training sets. Screens over multiple data sets to find compounds with potential malaria blood stage inhibitory activity have been used to generate multiple Bayesian models. Here we describe a method by which Bayesian quantitative structure-activity relationship models, which contain information on thousands to millions of proprietary compounds, can be shared between collaborators at both for-profit and not-for-profit institutions. This model-sharing paradigm allows for the development of consensus models that have increased predictive power over any single model and yet does not reveal the identity of any compounds in the training sets.

The existence of asymptomatically parasitemic individuals in malaria-endemic areas has long been recognised to signify naturally acquired immunity to malaria disease, resulting from control of the parasite’s asexual blood-stage. This has for many years been viewed as a ‘proof-of-concept’ encouraging the development of blood-stage vaccines (BSVs). Results of clinical trials of candidate subunit BSVs have mostly, however, not lived up to early expectations and the field is currently experiencing a challenging period.

This study analysed the dynamics of blood stage malaria with immune response and under administration of Coartem as a combination therapy. The techniques of mathematical modelling were used in coming up and analysing the deterministic model. Sensitivity analysis and statistical approaches were used to compare model simulated treatment results with the use of Coartem and other antimalarial drugs. We sought to theoretically assess if Coartem can bring improvement in the treatment of malaria as compared to the other drugs. Our analysis and numerical results suggest that Coartem compares well with other antimalarial drug that have been on the market. However, the shortfall of our model is that it could not give good comparative results between Coartem treatment and other combination treatment schemes with similar mode of action. Our study predicted effects of different drug treatment protocols in malaria using a theoretical mathematical model, which gives an insight into potential effective treatment schemes.

The Malaria Immunology Database (MalarImDB, www.malarimdb.org) is a novel literature-based database of host mediators in blood-stage malaria. We designed this open-access online tool because intensive malaria research has resulted in a dazzling complexity of host mediators with pathogenic or protective functions. MalarImDB allows comparisons between expression levels in humans, expression levels in murine models, and functional data from experimental treatments in mice. The database is equipped with multiple search engines to retrieve information from many published studies. The search output is visualized schematically in tables, thereby revealing similarities and disparities. Thus, the primary aim of this database is to present a clear overview of the currently available data about malaria and to simplify literature searches.

Item does not contain fulltext The development of a vaccine against malaria has public health priority. In a controlled setting, preliminary data on the efficacy of Plasmodium falciparum vaccine candidates can be obtained by exposing immunized human volunteers to the bites of laboratory-reared P. falciparum-infected mosquitoes. Using empirical data, we show that these trials, with small numbers of volunteers, are sufficiently powered to detect protective biological effects induced by preerythrocytic and/or blood-stage candidate vaccines if parasitemia is measured daily by quantitative polymerase chain reaction. Sporozoite challenge trials are thus a powerful tool for early selection of candidates that warrant efficacy of trials in the field. 01 augustus 2012

Malaria fever is highly periodic and is associated with the parasite replication cycles in red blood cells. The existence of periodicity in malaria infection demonstrates that parasite replication in different red blood cells is synchronized. In this article, rigorous mathematical analysis of an age-structured human malaria model of infected red blood cells (Rouzine and McKenzie, Proc Natl Acad Sci USA 100:3473-3478, 2003) is provided and the synchronization of Plasmodium falciparum erythrocytic stages is investigated. By using the replication rate as the bifurcation parameter, the existence of Hopf bifurcation in the age-structured malaria infection model is obtained. Numerical simulations indicate that synchronization with regular periodic oscillations (of period 48 h) occurs when the replication rate increases. Therefore, Kwiatkowski and Nowak's observation (Proc Natl Acad Sci USA 88:5111-5113, 1991) that synchronization could be generated at modest replication rates is confirmed.

Malaria, a disease caused by the protozoan parasite Plasmodium, remains a serious healthcare problem in developing countries worldwide. While the host-parasite relationship in humans has been difficult to determine, the pliability of murine malaria models has enabled valuable contributions to the understanding of the pathogenesis of disease. Although no single model reflects precisely malaria infection of the human, different models collectively provide important information on the mechanisms of protective immunity and immunopathogenesis. This review summarizes progress towards understanding the broad spectrum of immune responsiveness to the blood stages of the malaria parasite during experimental infections in mice and highlights how examination of murine malarias sheds light on the factors involved in the modulation of vaccine-potentiated immunity.

Malaria is a global health problem and the need for a vaccine that could prevent millions of deaths annually cannot be further justified. A number of strategies have been adopted in the pursuit of making a successful malaria vaccine including the use of blood stage antigens which would primarily target the merozoite and prevent its replication through the asexual blood cycle of the parasite. In this regard, merozoite surface proteins have gained a lot of attention by the malaria vaccine fraternity for development as subunit vaccines. In spite of concentrated efforts spanning a long number of years, we are not close on producing a successful blood stage vaccine, especially one based on merozoite surface proteins (MSP). However, a recent systematic review with meta-analysis of 33 different studies has reported that antibodies against MSP proteins (MSP-1(19) and MSP-3) exhibit the strongest association with lower incidence of malaria and protection. Also the efficacy of an MSP based vaccine, Combination B, in significantly reducing parasite density among infected children in Papua New Guinea supports the development of MSP based malaria vaccines. In light of these developments, in this commentary, we address different aspects and concerns about MSP based vaccines-the need to develop MSP based blood stage malaria vaccines, our successes and failures from the current and past MSP vaccine trails, the lessons learnt from these studies, the future directions and challenges that still face us.

Plasmodium falciparum malaria is a major global health problem, responsible for up to 1 million deaths each year. Major efforts have been made to develop an effective vaccine against this disease, to reduce the associated morbidity and mortality. There has already been considerable progress, with the first vaccine against the pre-erythrocytic stages of P. falciparum now en route to licensure. There remains, however, a strong scientific rationale for the development of a highly effective additional vaccine component against the blood stages of the parasite, which could be deployed in conjunction with partially effective control measures against the pre-erythrocytic stages. Here, recent progress in the clinical development of blood-stage vaccines is reviewed, including methods of antigen selection, the limitations of in-vitro assays for selecting vaccines for clinical development, and the results of recently published clinical trials. This review seeks to summarize recent developments in our understanding of immunity to blood-stage parasites, as well as the relevant key advances made in vaccine technologies over the last decade. The future challenges that face this field of vaccine research are also described.

Item does not contain fulltext Development and optimization of first generation malaria vaccine candidates has been facilitated by the existence of a well-established Plasmodium falciparum clinical challenge model in which infectious sporozoites are administered to human subjects via mosquito bite. While ideal for testing pre-erythrocytic stage vaccines, some researchers believe that the sporozoite challenge model is less appropriate for testing blood stage vaccines. Here we report a consultation, co-sponsored by PATH MVI, USAID, EMVI and WHO, where scientists from all institutions globally that have conducted such clinical challenges in recent years and representatives from regulatory agencies and funding agencies met to discuss clinical malaria challenge models. Participants discussed strengthening and harmonizing the sporozoite challenge model and considered the pros and cons of further developing a blood stage challenge possibly better suited for evaluating the efficacy of blood stage vaccines. This report summarizes major findings and recommendations, including an update on the Plasmodium vivax clinical challenge model, the prospects for performing experimental challenge trials in malaria endemic countries and an update on clinical safety data. While the focus of the meeting was on the optimization of clinical challenge models for evaluation of blood stage candidate malaria vaccines, many of the considerations are relevant for the application of challenge trials to other purposes.

The aim of this article is to highlight the challenges that researchers face in the development of asexual blood-stage vaccines, and the progress made recently towards achieving the goal of a successful candidate to reduce morbidity.There is good rationale to support the development of blood-stage malaria vaccines, the most promising being the demonstration that nonimmune volunteers repeatedly challenged and cured with blood-stage parasites developed immunity to subsequent challenge as well as the demonstration of the efficacy of the first asexual blood-stage vaccine tested in a malaria endemic area (combination B) to reduce parasite density in children. The selective pressure induced by this vaccine and the accumulating evidence of extensive antigenic diversity of blood-stage proteins pose a difficult challenge to vaccine researchers. Numerous clinical trials, both in nonendemic and endemic areas, are being conducted with different antigens, different allelic types and different protein fragments.Considerable efforts and funding are available to shift from laboratory experiments to field trials. Field trials remain the definitive method to assess the real impact of different vaccines in the target populations. More rigorous side-by-side comparisons are needed between the different vaccines using standardized in-vitro and in-vivo testing, so that the most promising candidates will be selected for further development.

There are 300-500 million cases of malaria each year and of the more than one million people that die each year from malaria, most are children under 5 years of age. The cloning of malaria antigens in 1983 offered great hope of developing a viable subunit vaccine. While some subunit vaccines have shown great promise in model systems, an efficacious human vaccine is still not available. Immunological studies have shown that numerous factors such as parasite's antigenic variation and polymorphism, immunological non-responsiveness to individual vaccine antigens, parasite-induced apoptosis of immune effector and memory cells, immune deviation as a result of maternal immunity and alterations of dendritic cell function can impede the development of vaccines. These findings indicate that alternative novel approaches are required to tackle the disease and induce protection against malaria.

The development of malaria blood-stage vaccines is gathering momentum: there are several new funding initiatives, one multiantigen formulation is currently being tested and at least one other blood-stage vaccine is expected to begin trials in 2001. However, there is no consensus over the best way to select which form of an antigen to take into clinical testing. There is thus a danger that less-effective vaccines might be tested in the field in the order of their availability, rather than merit. Here, we argue that first proving efficacy in the New World monkey challenge model would accelerate development.

Nature Communications 2: Article number: 601 (2011); Published: 20 December 2011; Updated: 19 September 2013. In the Methods section of this Article, the species of the tissue plasminogen activator secretory signal used in adenovirus vector construction was stated incorrectly and should have been given as human.

Protection against malaria from a vaccine requires modulation of the immune response to malaria antigens. This modulation by pathogen-derived molecules is explored in this study. Human immune cells synergistically express signaling proteins when stimulated by certain combinations of pathogen-derived molecules. Some of these expression profiles indicate a Th1-mediated immune response, which may be the immune response needed for the next-generation malaria of vaccines, in terms of effectiveness.

Although a clearer understanding of the underlying mechanisms involved in protection and immunopathology during blood-stage malaria has emerged, the mechanisms involved in regulating the adaptive immune response especially those required to maintain a balance between beneficial and deleterious responses remain unclear. Recent evidence suggests the importance of CD11c⁺ dendritic cells (DC) and CD4⁺Foxp3⁺ regulatory T cells in regulating immune responses during infection and autoimmune disease, but information concerning the contribution of these cells to regulating immunity to malaria is limited. Here, we review recent findings from our laboratory and others in experimental models of malaria in mice and in Plasmodium-infected humans on the roles of DC and natural regulatory T cells in regulating adaptive immunity to blood-stage malaria.

The development of a malaria vaccine seems to be a definite possibility despite the fact that even individuals with a life time of endemic exposure do not develop sterile immunity. An effective malaria vaccine would be invaluable in preventing malaria-associated deaths in endemic areas, especially amongst children less than 5 years of age and pregnant women. This review discusses our current understanding of immunity against the asexual blood stage of malaria - the stage that is responsible for the symptoms of the disease - and approaches to the design of an asexual blood stage vaccine.

The authors discuss results from an early trial of a vaccine based on Plasmodium MSP-3 protein reported by Pierre Druilhe and colleagues.

In summary, the host has no shortage of potential cytotoxic molecules for the intraerythrocyte stage, but for most of these it remains to be established whether they really play a significant role in resistance to infection

In this report we will review some of the attempts carried out by the different research groups around the world, focusing toward the end on the work conducted at the Instituto de Immunologia, Hospital San Juan de Dios, Bogota, Colombia