The pathophysiology of malaria

A progress report in advancements of heterocyclic compounds as novel antimalarial agents over the last 5 years

Malaria, caused by Plasmodium parasites and transmitted by Anopheles mosquitoes, remains a significant global health challenge, especially in tropical and subtropical regions where the disease is endemic. The complex Plasmodium lifecycle, involving stages in both the liver and bloodstream, leads to symptoms such as high fever, anemia, and, in severe cases, life-threatening complications, particularly P. falciparum infections. While historical treatments such as quinine and modern therapies such as artemisinin-based combination therapies (ACTs) have been effective, the growing issue of drug and insecticide resistance undermines these efforts. This resistance has spurred the need for new antimalarial drugs and strategies. Among the promising areas of research are heterocyclic compounds, which, due to their diverse and versatile chemical structures, are being investigated for their ability to disrupt the Plasmodium lifecycle. These compounds have potential as novel therapeutic agents that could enhance current treatment options. Understanding the mechanisms underlying drug resistance and advancing these therapeutic innovations are crucial for maintaining effective malaria control and treatment, highlighting the importance of on-going research in this field.

Association between RANTES/CCL5 levels with Plasmodium infections and malaria severity: a systematic review

BACKGROUND

Malaria continues to be a significant global health concern, and developing effective therapeutic strategies requires an understanding of the immune response to the disease. This systematic review synthesized the current body of research on the role of regulated on activation, normal T cell expressed and secreted (RANTES)-in the pathogenesis and disease severity of malaria.

METHODS

A systematic review protocol was registered with PROSPERO under the registration number CRD42024535822. The systematic review was conducted following PRISMA guidelines to identify studies examining RANTES levels in individuals infected with Plasmodium species. Searches were performed across multiple databases, including ProQuest, Journals@Ovid, Embase, Scopus, PubMed, and MEDLINE. Further searches were performed in Google Scholar. Quality assessment was done using the Joanna Briggs Institute (JBI) critical appraisal tools. Alterations in RANTES levels in patients with malaria were synthesized narratively.

RESULTS

A comprehensive search of major databases identified 22 studies meeting inclusion criteria, predominantly focusing on Plasmodium falciparum and Plasmodium vivax infections. RANTES levels were found to vary significantly across different severities of malaria, with several studies reporting lower levels in severe cases compared to non-malarial controls. However, inconsistencies were observed in the alterations of RANTES levels between severe and non-severe malaria cases.

CONCLUSION

Taken together, the finding of this systematic review underscore the complex regulation of RANTES in malaria pathophysiology. Future research should focus on longitudinal assessments to elucidate the dynamic role of RANTES throughout the course of malaria and recovery, to potentially inform the design of novel therapeutic strategies.

Cytological and histopathological bone marrow findings in dogs with natural Babesia rossi infection

An inappropriate regenerative response to anaemia has been reported in B. rossi-associated canine babesiosis. We investigated the impact of canine babesiosis on the bone marrow by evaluating the cytological and histopathological changes. Bone marrow smears and histopathology specimens were obtained post-mortem (within 24 hours of death) from six Babesia rossi-infected dogs and five healthy control dogs. Findings were interpreted together with the circulating haemogram, a Perls' Prussian blue special stain for iron and immunohistochemical markers CD3, CD20, MUM-1, MAC387 and CD204. Infected dogs had an inflammatory leukogram, inappropriately regenerative anaemia, hypercellular bone marrow due to erythroid hyperplasia, dyserythropoietic changes within the metarubricyte population, a myeloid hyperplasia with a left shift, a significant increase in the number of CD204-positive resident macrophages, a left shift within the megakaryocyte population and a significantly increased iron content. Whether iron-restricted erythropoiesis plays a role in the anaemia of canine babesiosis could not be established in this study. Our findings concur with what has been recorded in the bone marrow of humans with falciparum malaria and confirm that dyserythropoiesis is partially responsible for the inappropriate erythroid response in canine babesiosis.

The mRNA content of plasma extracellular vesicles provides a window into molecular processes in the brain during cerebral malaria

The impact of cerebral malaria on the transcriptional profiles of cerebral tissues is difficult to study using noninvasive approaches. We isolated plasma extracellular vesicles (EVs) from patients with cerebral malaria and community controls and sequenced their mRNA content. Deconvolution analysis revealed that EVs from cerebral malaria are enriched in transcripts of brain origin. We ordered the patients with cerebral malaria based on their EV-transcriptional profiles from cross-sectionally collected samples and inferred disease trajectory while using healthy community controls as a starting point. We found that neuronal transcripts in plasma EVs decreased with disease trajectory, whereas transcripts from glial, endothelial, and immune cells increased. Disease trajectory correlated positively with severity indicators like death and was associated with increased VEGFA-VEGFR and glutamatergic signaling, as well as platelet and neutrophil activation. These data suggest that brain tissue responses in cerebral malaria can be studied noninvasively using EVs circulating in peripheral blood.

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.

A detailed kinetic model of glycolysis in Plasmodium falciparum-infected red blood cells for antimalarial drug target identification

Upon infection by the malaria parasite Plasmodium falciparum, the glycolytic rate of a red blood cell increases up to 100-fold, possibly contributing to lactic acidosis and hypoglycemia in patients with severe malaria. This dramatic increase in glucose uptake and metabolism was correctly predicted by a newly constructed detailed enzyme kinetic model of glucose metabolism in the trophozoite-infected red blood cell. Subsequently, we expanded the model to simulate an infected red blood cell culture, including the different asexual blood-stage forms of the malaria parasite. The model simulations were in good agreement with experimental data, for which the measured parasitic volume was an important parameter. Upon further analysis of the model, we identified glucose transport as a drug target that would specifically affect infected red blood cells, which was confirmed experimentally with inhibitor titrations. This model can be a first step in constructing a whole-body model for glucose metabolism in malaria patients to evaluate the contribution of the parasite's metabolism to the disease state.

Nasr O. A Novel Ensemble Weight-Assisted Yolov5-Based Deep Learning Technique for the Localization and Detection of Malaria Parasites

The traditional way of diagnosing malaria takes time, as physicians have to check about 5000 cells to produce the final report. The accuracy of the final report also depends on the physician’s expertise. In the event of a malaria epidemic, a shortage of qualified physicians can become a problem. In the manual method, the parasites are identified by visual identification; this technique can be automated with the use of new algorithms. There are numerous publicly available image datasets containing the intricate structure of parasites, and deep learning algorithms can recognize these complicated patterns in the images. This study aims to identify and localize malaria parasites in the photograph of blood cells using the YOLOv5 model. In this research, a publicly available malaria trophozoite dataset is utilized which contains 1182 data samples. YOLOv5, with the novel technique of weight ensemble and traditional transfer learning, is trained using this dataset, and the results were compared with the other object detection models—for instance, Faster RCNN, SSD net, and the hybrid model. It was observed that YOLOv5 with the ensemble weights yields better results in terms of precision, recall, and mAP values: 0.76, 0.78, and 0.79, respectively. The mAP score closer to 1 signifies a higher confidence in localizing the parasites. This study is the first implementation of ensemble YOLOv5 in the malaria parasite detection field. The proposed ensemble model can detect the presence of malaria parasites and localize them with bounding boxes better than previously used models.

Molecular profiling reveals features of clinical immunity and immunosuppression in asymptomatic P. falciparum malaria

Clinical immunity to P. falciparum malaria is non-sterilizing, with adults often experiencing asymptomatic infection. Historically, asymptomatic malaria has been viewed as beneficial and required to help maintain clinical immunity. Emerging views suggest that these infections are detrimental and constitute a parasite reservoir that perpetuates transmission. To define the impact of asymptomatic malaria, we pursued a systems approach integrating antibody responses, mass cytometry, and transcriptional profiling of individuals experiencing symptomatic and asymptomatic P. falciparum infection. Defined populations of classical and atypical memory B cells and a T_H2 cell bias were associated with reduced risk of clinical malaria. Despite these protective responses, asymptomatic malaria featured an immunosuppressive transcriptional signature with upregulation of pathways involved in the inhibition of T-cell function, and CTLA-4 as a predicted regulator in these processes. As proof of concept, we demonstrated a role for CTLA-4 in the development of asymptomatic parasitemia in infection models. The results suggest that asymptomatic malaria is not innocuous and might not support the induction of immune processes to fully control parasitemia or efficiently respond to malaria vaccines.

Epileptogenesis in Common Parasitic Infections

Purpose of the review

Neurocysticercosis (NCC) has been well recognized as a leading cause of epilepsy. More recently, studies of other parasitic diseases such as cerebral malaria (CM) and onchocerciasis are yielding novel insights into the pathogenesis of parasite-associated epilepsy. We compare the clinical and electrophysiological findings in epilepsy associated with these highly prevalent parasites and discuss the mechanisms involved in epileptogenesis.

Recent Findings

Electrophysiological and imaging biomarkers continue to emerge, and individuals who are at-risk of developing parasite-associated epilepsies are being identified with greater reliability. While both Taenia solium and Plasmodium falciparum directly affect the brain parenchyma, Onchocerca volvulus is not known to invade the central nervous system. Thus, the causal association between O. volvulus and epilepsy remains controversial.

Summary

Both NCC and CM have a well-defined acute phase when the parasites directly or indirectly invade the brain parenchyma and lead to local inflammatory changes. This is followed by a chronic phase marked by recurrent seizures. However, these stages of epileptogenic process have not been identified in the case of O. volvulus.

In pursuit of new anti-malarial candidates: novel synthesized and characterized pyrano-benzodioxepin analogues attenuated Plasmodium berghei replication in malaria-infected mice

Malaria, a parasitic disease, is one of the major causes of morbidity and mortality, particularly in the tropics. Following the increased resistance of the primary causative parasite, Plasmodium sp, to the mainstream drug, artemisinin combination therapies (ACTs), combating malaria incidences, morbidity and mortality have remained elusive. Novel pyrano-benzodioxepin derivatives (DHA-PABA and DHA-LEVO) were synthesized and characterized using Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopies. The compounds were subjected to standard in vivo antimalarial screening (using chloroquine-sensitive strain) in mice, and the toxicity was also determined using a standard assay. The observed elevation in serum alkaline phosphatase and acid phosphatase activity in the untreated and the group administered lower doses of DHA-LEVO is an indication of the hepatic stage of the parasite in the experimental animal, which is accompanied by significant perturbation in the membrane of the hepatocyte leading to leakage of this enzyme out of the liver cells. The semisynthetic pyrano-benzodioxepin derivatives act rapidly by clearing the parasite load from the blood. The novel pyrano-benzodioxepin candidates containing endoperoxide functionality hold promise in the pursuit of new monotherapy drug candidates against the virulent strain of the plasmodium.

Protective Effects of Gymnema inodorum Leaf Extract on Plasmodium berghei-Induced Hypoglycemia, Dyslipidemia, Liver Damage, and Acute Kidney Injury in Experimental Mice

Malaria complications are the most frequent cause of mortality from parasite infection. This study is aimed at investigating the protective effect of Gymnema inodorum leaf extract (GIE) on hypoglycemia, dyslipidemia, liver damage, and acute kidney injury induced by Plasmodium berghei infection in mice. Groups of ICR mice were inoculated with 1 × 10⁷ parasitized erythrocytes of P. berghei ANKA and administered orally by gavage with 100, 250, and 500 mg/kg of GIE for 4 consecutive days. Healthy and untreated controls were given distilled water, while the positive control was treated with 10 mg/kg of chloroquine. The results showed that malaria-associated hypoglycemia, dyslipidemia, liver damage, and acute kidney injury were found in the untreated mice as indicated by the significant alteration of biological markers. On the contrary, in 250 and 500 mg/kg of GIE-treated mice, the biological markers were normal compared to healthy controls. The highest protective effect was found at 500 mg/kg similar to the CQ-treated group. However, GIE at a dose of 100 mg/kg did not show protection during malaria infection. This study demonstrated that GIE presented potential therapeutic effects on PbANKA-induced hypoglycemia, dyslipidemia, liver damage, and acute kidney injury. The results obtained confirm the prospect of G. inodorum as an essential source of new antimalarial compounds and justify folkloric use as an alternative malarial treatment.

Real-time Malaria Parasite Screening in Thick Blood Smears for Low-Resource Setting

Malaria is a serious public health problem in many parts of the world. Early diagnosis and prompt effective treatment are required to avoid anemia, organ failure, and malaria-associated deaths. Microscopic analysis of blood samples is the preferred method for diagnosis. However, manual microscopic examination is very laborious and requires skilled health personnel of which there is a critical shortage in the developing world such as in sub-Saharan Africa. Critical shortages of trained health personnel and the inability to cope with the workload to examine malaria slides are among the main limitations of malaria microscopy especially in low-resource and high disease burden areas. We present a low-cost alternative and complementary solution for rapid malaria screening for low resource settings to potentially reduce the dependence on manual microscopic examination. We develop an image processing pipeline using a modified YOLOv3 detection algorithm to run in real time on low-cost devices. We test the performance of our solution on two datasets. In the dataset collected using a microscope camera, our model achieved 99.07% accuracy and 97.46% accuracy on the dataset collected using a mobile phone camera. While the mean average precision of our model is on par with human experts at an object level, we are several orders of magnitude faster than human experts as we can detect parasites in images as well as videos in real time.

Historical chemical annotations of Cinchona bark collections are comparable to results from current day high-pressure liquid chromatography technologies

ETHNOPHARMACOLOGICAL RELEVANCE

Species of the genus Cinchona (Rubiaceae) have been used in traditional medicine, and as a source for quinine since its discovery as an effective medicine against malaria in the 17th century. Despite being the sole cure of malaria for almost 350 years, little is known about the chemical diversity between and within species of the antimalarial alkaloids found in the bark. Extensive historical Cinchona bark collections housed at the Royal Botanic Gardens, Kew, UK, and in other museums may shed new light on the alkaloid chemistry of the Cinchona genus and the history of the quest for the most effective Cinchona barks.

AIM OF THE STUDY

We used High-Pressure Liquid Chromatography (HPLC) coupled with fluorescence detection (FLD) to reanalyze a set of Cinchona barks originally annotated for the four major quinine alkaloids by John Eliot Howard and others more than 150 years ago.

MATERIALS AND METHODS

We performed an archival search on the Cinchona bark collections in the Economic Botany Collection housed in Kew, focusing on those with historical alkaloid content information. Then, we performed HPLC analysis of the bark samples to separate and quantify the four major quinine alkaloids and the total alkaloid content using fluorescence detection. Correlations between historic and current annotations were calculated using Spearman's rank correlation coefficient, before paired comparisons were performed using Wilcox rank sum tests. The effects of source were explored using generalized linear modelling (GLM), before the significance of each parameter in predicting alkaloid concentrations were assessed using chi-square tests as likelihood ratio testing (LRT) models.

RESULTS

The total alkaloid content estimation obtained by our HPLC analysis was comparatively similar to the historical chemical annotations made by Howard. Additionally, the quantity of two of the major alkaloids, quinine and cinchonine, and the total content of the four alkaloids obtained were significantly similar between the historical and current day analysis using linear regression.

CONCLUSIONS

This study demonstrates that the historical chemical analysis by Howard and current day HPLC alkaloid content estimations are comparable. Current day HPLC analysis thus provide a realistic estimate of the alkaloid contents in the historical bark samples at the time of sampling more than 150 years ago. Museum collections provide a powerful but underused source of material for understanding early use and collecting history as well as for comparative analyses with current day samples.

Fungal and Parasitic CNS Infections

Central nervous system fungal infections can be broadly divided into those that infect a healthy host such as Cryptococcus, Coccidioides, Histoplasma, Blastomyces, Sporothrix spp., and those that cause opportunistic infections in an immunocompromised host such as Candida, Aspergillus, Zygomycetes, Trichosporon spp. The clinical manifestations of central nervous system fungal infections commonly seen in children in clinical practice include a chronic meningitis or meningoencephalitis syndrome, brain abscess, rhino-cerebral syndrome and rarely, a fungal ventriculitis. Fungal central nervous system infections should be suspected in any child with subacute to chronic febrile encephalopathy or meningitis with or without raised intracranial pressure, seizures, orbital pain and/or sero-sanguinous nasal discharge. Diagnosis is corroborated by cerebrospinal fluid analysis, culture and PCR, special stains, serological tests and neuroimaging. Management of fungal central nervous system infections include specific antifungal therapy and supportive measures for associated problems, management of underlying predisposing condition and surgical intervention in cases with localized disease, abscess or presence of simultaneous foreign body such as intracranial shunts. In addition to the fungi, several parasitic infections can cause central nervous system infections in children. Of these, authors briefly discuss cerebral malaria, and amebic meningo-encephalitis.

'2TM proteins': an antigenically diverse superfamily with variable functions and export pathways

Malaria is a disease that affects millions of people annually. An intracellular habitat and lack of protein synthesizing machinery in erythrocytes pose numerous difficulties for survival of the human pathogen Plasmodium falciparum. The parasite refurbishes the infected red blood cell (iRBC) by synthesis and export of several proteins in an attempt to suffice its metabolic needs and evade the host immune response. Immune evasion is largely mediated by surface display of highly polymorphic protein families known as variable surface antigens. These include the two trans-membrane (2TM) superfamily constituted by multicopy repetitive interspersed family (RIFINs), subtelomeric variable open reading frame (STEVORs) and Plasmodium falciparum Maurer's cleft two trans-membrane proteins present only in P. falciparum and some simian infecting Plasmodium species. Their hypervariable region flanked by 2TM domains exposed on the iRBC surface is believed to generate antigenic diversity. Though historically named "2TM superfamily," several A-type RIFINs and some STEVORs assume one trans-membrane topology. RIFINs and STEVORs share varied functions in different parasite life cycle stages like rosetting, alteration of iRBC rigidity and immune evasion. Additionally, a member of the STEVOR family has been implicated in merozoite invasion. Differential expression of these families in laboratory strains and clinical isolates propose them to be important for host cell survival and defense. The role of RIFINs in modulation of host immune response and presence of protective antibodies against these surface exposed molecules in patient sera highlights them as attractive targets of antimalarial therapies and vaccines. 2TM proteins are Plasmodium export elements positive, and several of these are exported to the infected erythrocyte surface after exiting through the classical secretory pathway within parasites. Cleaved and modified proteins are trafficked after packaging in vesicles to reach Maurer's clefts, while information regarding delivery to the iRBC surface is sparse. Expression and export timing of the RIFIN and Plasmodium falciparum erythrocyte membrane protein1 families correspond to each other. Here, we have compiled and comprehended detailed information regarding orthologues, domain architecture, surface topology, functions and trafficking of members of the "2TM superfamily." Considering the large repertoire of proteins included in the 2TM superfamily and recent advances defining their function in malaria biology, a surge in research carried out on this important protein superfamily is likely.

Dysregulation of pulmonary endothelial protein C receptor and thrombomodulin in severe falciparum malaria-associated ARDS relevant to hemozoin

To investigate the role of the protein C system, endothelial protein C receptor (EPCR) and thrombomodulin (TM) in the pathogenesis of malaria-associated acute respiratory distress syndrome (ARDS) in relation to hemozoin and proinflammatory cytokines-induced type II pneumocyte injury and -aggravated pulmonary resolution. A total of 29 left-over lung specimens that were obtained from patients who died from severe falciparum malaria were examined. Histopathological, immunohistochemical and electron microscopic analyses revealed that ARDS coexisted with pulmonary edema and systemic bleeding; the severity was dependent on the level of hemozoin deposition in the lung and internal alveolar hemorrhaging. The loss of EPCR and TM was primarily identified in ARDS patients and was related to the level of hemozoin, parasitized red blood cell (PRBC) and white blood cell accumulation in the lung. Moreover, an in vitro analysis demonstrated that interleukin-13 and -31 and hemozoin induced pneumocytic cell injury and apoptosis, as assessed by EB/AO staining, electron microscopy and the up-regulation of CARD-9 mRNA (caspase recruitment domain-9 messenger-ribonucleic acid). The dysregulation of EPCR and TM in the lung, especially in those with increased levels of hemozoin, may play an important role in the pathogenesis of malaria-associated ARDS through an apoptotic pathway.

RANTES levels as a determinant of falciparum malaria severity or recovery

The study explored the role of differential RANTES concentrations, its receptor CCR5 expression and resulting immunomodulation in the pathogenesis and/or recovery from falciparum malaria. The study population included cases of uncomplicated malaria (UC-M, N=128, enrolled on follow-up basis), severe malaria (SM, N=25), and healthy controls (N=112). Serum RANTES and TNF-α levels were evaluated by ELISA. Monocyte levels and activation profile were studied by flow cytometry. Differential mRNA expression profile was studied by real-time PCR. Blood parasite count was evaluated by registered pathologists. RANTES concentration was significantly downregulated in SM cases compared to UC-M (P=.046) and controls (P<.001). Expression of monocyte marker mCD14, activation markers CCR5 and CD40, and downstream effector cytokine TNF-α was significantly higher in malaria cases compared to controls, in SM cases compared to UC-M. TNF-α expression correlated positively with CD40 and CCR5 expressions. Follow-up-based analysis showed that RANTES concentrations increased on recovery compared to baseline in UC-M cases (P=.106) and inversely correlated with malaria parasite load, mCD14, CCR5 and CD40, and TNF-α expressions. These findings suggest an important association of RANTES concentrations in Plasmodium falciparum malaria disease pathogenesis, as well as recovery, mediated through differential modulation and regulated activation of monocytes and cytokine TNF-α.

GENETIC RELATIONSHIPS BETWEEN PARASITE VIRULENCE AND TRANSMISSION IN THE RODENT MALARIA PLASMODIUM CHABAUDI

Many parasites evolve to become virulent rather than benign mutualists. One of the major theoretical models of parasite virulence postulates that this is because rapid within-host replication rates are necessary for successful transmission (parasite fitness) and that virulence (damage to the host) is an unavoidable consequence of this rapid replication. Two fundamental assumptions underlying this so-called evolutionary trade-off model have rarely been tested empirically: (1) that higher replication rates lead to higher levels of virulence; and (2) that higher replication rates lead to higher transmission. Both of these relationships must have a genetic basis for this evolutionary hypothesis to be relevant. These assumptions were tested in the rodent malaria parasite, Plasmodium chabaudi, by examining genetic relationships between virulence and transmission traits across a population of eight parasite clones isolated from the wild. Each clone was injected into groups of inbred mice in a controlled laboratory environment, and replication rate (measured by maximum asexual parasitemia), virulence (measured by live-weight loss and degree of anemia in the mouse), and transmission (measured by density of sexual forms, gametocytes, in the blood and proportion of mosquitoes infected after taking a blood-meal from the mouse) were assessed. It was found that clones differed widely in these traits and these clone differences were repeatable over successive blood passages. Virulence traits were strongly phenotypically and genetically (i.e., across clones) correlated to maximum parasitemia thus supporting the first assumption that rapid replication causes higher virulence. Transmission traits were also positively phenotypically and genetically correlated to parasitemia, which supports the second assumption that rapid replication leads to higher transmission. Thus, two assumptions of the parasite-centered trade-off model of the evolution of virulence were shown to be justified in malaria parasites.

Expression of cleaved caspase-3 in renal tubular cells in Plasmodium falciparum malaria patients

AIM

In Plasmodium falciparum malaria, the clinical manifestation of acute kidney injury (AKI) is commonly associated with acute tubular necrosis (ATN) in the kidney tissues. Renal tubular cells often exhibit various degrees of cloudy swelling, cell degeneration, and frank necrosis. To study individual cell death, this study evaluates the degree of renal tubular necrosis in association with apoptosis in malarial kidneys.

METHODS

Kidney tissues from P. falciparum malaria with AKI (10 cases), and without AKI (10 cases) were evaluated for tubular pathology. Normal kidney tissues from 10 cases served as controls. Tubular necrosis was assessed quantitatively in kidney tissues infected with P. falciparum malaria, based on histopathological evaluation. In addition, the occurrence of apoptosis was investigated using cleaved caspase-3 marker. Correlation between tubular necrosis and apoptosis was analyzed.

RESULTS

Tubular necrosis was found to be highest in P. falciparum malaria patients with AKI (36.44% ± 3.21), compared to non-AKI (15.88% ± 1.63) and control groups (2.58% ± 0.39) (all p < 0.001). In the AKI group, the distal tubules showed a significantly higher degree of tubular necrosis than the proximal tubules (p = 0.021) and collecting tubules (p = 0.033). Tubular necrosis was significantly correlated with the level of serum creatinine (r = 0.596, p = 0.006), and the occurrence of apoptosis (r = 0.681, p = 0.001).

CONCLUSION

In malarial AKI, the process of apoptosis occurs in ATN.

Effects of sevuparin on rosette formation and cytoadherence of Plasmodium falciparum infected erythrocytes

In severe falciparum malaria cytoadherence of parasitised red blood cells (PRBCs) to vascular endothelium (causing sequestration) and to uninfected red cells (causing rosette formation) contribute to microcirculatory flow obstruction in vital organs. Heparin can reverse the underlying ligand-receptor interactions, but may increase the bleeding risks. As a heparin-derived polysaccharide, sevuparin has been designed to retain anti-adhesive properties, while the antithrombin-binding domains have been eliminated, substantially diminishing its anticoagulant activity. Sevuparin has been evaluated recently in patients with uncomplicated falciparum malaria, and is currently investigated in a clinical trial for sickle cell disease. The effects of sevuparin on rosette formation and cytoadherence of Plasmodium falciparum isolates from Thailand were investigated. Trophozoite stages of P. falciparum-infected RBCs (Pf-iRBCs) were cultured from 49 patients with malaria. Pf-iRBCs were treated with sevuparin at 37°C and assessed in rosetting and in cytoadhesion assays with human dermal microvascular endothelial cells (HDMECs) under static and flow conditions. The proportion of Pf-iRBCs forming rosettes ranged from 6.5% to 26.0% (median = 12.2%). Rosetting was dose dependently disrupted by sevuparin (50% disruption by 250 μg/mL). Overall 57% of P. falciparum isolates bound to HDMECs under static conditions; median (interquartile range) Pf-iRBC binding was 8.5 (3.0–38.0) Pf-iRBCs/1000 HDMECs. Sevuparin in concentrations ≥ 100 μg/mL inhibited cytoadherence. Sevuparin disrupts P. falciparum rosette formation in a dose dependent manner and inhibits cytoadherence to endothelial cells. The data support assessment of sevuparin as an adjunctive treatment to the standard therapy in severe falciparum malaria.

Emerging concepts in T follicular helper cell responses to malaria

Antibody responses to malaria and candidate malaria vaccines are short-lived in children, leaving them susceptible to repeated malaria episodes. Because T follicular helper (T_FH) cells provide critical help to B cells to generate long-lived antibody responses, they have become the focus of recent studies of Plasmodium-infected mice and humans. The emerging data converge on common themes, namely, that malaria-induced T_H1 cytokines are associated with the activation of (i) T-like memory T_FH cells with impaired B cell helper function, and (ii) pre-T_FH cells that acquire Th1-like features (T-bet expression, IFN-γ production), which impede their differentiation into fully functional T_FH cells, thus resulting in germinal center dysfunction and suboptimal antibody responses. Deeper knowledge of T_FH cells in malaria could illuminate strategies to improve vaccines through modulating T_FH cell responses. This review summarizes emerging concepts in T_FH cell responses to malaria.

Antiparasitic and disease-modifying activity of Nyctanthes arbor-tristis Linn. in malaria: An exploratory clinical study

BACKGROUND

An unceasing threat of drug resistance continuously poses demand for new antimalarial drugs. A scientific assessment of traditionally used antimalarial plants through reverse pharmacology is crucial for a fast track drug discovery. An Ayurvedic plant Nyctanthes arbor-tristis Linn. - (Parijat) is being used in clinical practice and had shown antimalarial activity, with a parasite clearance in 76.6% of 120 patients, in an earlier clinical study.

OBJECTIVE

To further explore antimalarial potential of the plant through additional objective markers.

MATERIALS AND METHODS

An open-labelled observational study was conducted at M.A. Podar Hospital - Ayurveda (MAPH-A) after ethics committee approval. Administration of a paste of 5 fresh leaves, thrice a day for a week was a standard practice for management of malaria at MAPH-A. Clinical activity of N. arbor-tristis was evaluated by monitoring pyrexia, parasitemia and morbidity score (MS) in twenty patients. In addition, immune and biochemical markers and organ functions were monitored for objective markers of response. Student's paired-'t' test was applied to assess statistical significance.

RESULTS

Ten out of 20 patients showed both fever and parasite clearance, which was confirmed by polymerase chain reaction. Remaining ten patients had persistent but decreasing parasitemia. Four of them needed chloroquine as a fail-safe procedure. Irrespective of the degree of parasitemia all the patients showed decrease in MS. There was also an increase in platelet count and normalization of plasma lactic acid. There was a good clinical tolerability and an improvement in organ function. The inflammatory cytokines showed a reduction; particularly in TNF-α within a day.

CONCLUSIONS

At the given dosage, N. arbor-tristis showed disease-modifying activity; early clinical recovery with a decline of TNF-α and a gradual parasite clearance. Further studies with a standardised formulation for dose-searching and optimizing the treatment schedule are needed in a larger sample size.

CLINICAL TRIAL REGISTRATION NO

The process of trial registration had not begun when the study was conducted in 2000.

Assessment of submicroscopic infections and gametocyte carriage of Plasmodium falciparum during peak malaria transmission season in a community-based cross-sectional survey in western Kenya, 2012

Background

Although malaria control intervention has greatly decreased malaria morbidity and mortality in many African countries, further decline in parasite prevalence has stagnated in western Kenya. In order to assess if malaria transmission reservoir is associated with this stagnation, submicroscopic infection and gametocyte carriage was estimated. Risk factors and associations between malaria control interventions and gametocyte carriage were further investigated in this study.

Methods

A total of 996 dried blood spot samples were used from two strata, all smear-positives (516 samples) and randomly selected smear-negatives (480 samples), from a community cross-sectional survey conducted at peak transmission season in 2012 in Siaya County, western Kenya. Plasmodium falciparum parasite presence and density were determined by stained blood smear and by 18S mRNA transcripts using nucleic acid sequence-based amplification assay (NASBA), gametocyte presence and density were determined by blood smear and by Pfs25 mRNA-NASBA, and gametocyte diversity by Pfg377 mRNA RT-PCR and RT-qPCR.

Results

Of the randomly selected smear-negative samples, 69.6 % (334/480) were positive by 18S-NASBA while 18S-NASBA detected 99.6 % (514/516) smear positive samples. Overall, 80.2 % of the weighted population was parasite positive by 18S-NASBA vs 30.6 % by smear diagnosis and 44.0 % of the weighted population was gametocyte positive by Pfs25-NASBA vs 2.6 % by smear diagnosis. Children 5–15 years old were more likely to be parasitaemic and gametocytaemic by NASBA than individuals >15 years old or children <5 years old while gametocyte density decreased with age. Anaemia and self-reported fever within the past 24 h were associated with increased odds of gametocytaemia. Fever was also positively associated with parasite density, but not with gametocyte density. Anti-malarial use within the past 2 weeks decreased the odds of gametocytaemia, but not the odds of parasitaemia. In contrast, recent anti-malarial use was associated with lowered parasite density, but not the gametocyte density. Use of ITNs was associated with lower odds for parasitaemia in part of the study area with a longer history of ITN interventions. In the same part of study area, the odds of having multiple gametocyte alleles were also lower in individuals using ITNs than in those not using ITNs and parasite density was positively associated with gametocyte diversity.

Conclusion

A large proportion of submicroscopic parasites and gametocytes in western Kenya might contribute to the stagnation in malaria prevalence, suggesting that additional interventions targeting the infectious reservoir are needed. As school aged children and persons with anaemia and fever were major sources for gametocyte reservoir, these groups should be targeted for intervention and prevention to reduce malaria transmission. Anti-malarial use was associated with lower parasite density and odds of gametocytaemia, but not the gametocyte density, indicating a limitation of anti-malarial impact on the transmission reservoir. ITN use had a protective role against parasitaemia and gametocyte diversity in western Kenya.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1482-4) contains supplementary material, which is available to authorized users.

Different Regions of Plasmodium falciparum Erythrocyte-Binding Antigen 175 Induce Antibody Responses to Infection of Varied Efficacy

BACKGROUND

Increasing evidence suggests that antibodies against merozoite proteins involved in Plasmodium falciparum invasion into the red blood cell play an important role in clinical immunity to malaria. Erythrocyte-binding antigen 175 (EBA-175) is the best-characterized P. falciparum invasion ligand, reported to recognize glycophorin A on the surface of erythrocytes. Its protein structure comprises 6 extracellular regions. Whereas region II contains Duffy binding-like domains involved in the binding to glycophorin A, the functional role of regions III-V is less clear.

METHODS

We developed a novel cytometric bead array for assessment of antigen-specific antibody concentration in plasma to evaluate the efficacy of immune responses to different regions of EBA-175 and associations between antibody levels with protection from symptomatic malaria in a treatment-reinfection cohort study.

RESULTS

We found that while antibodies to region II are highly abundant, circulating levels as low as 5-10 µg/mL of antibodies specific for region III or the highly conserved regions IV-V predict strong protection from clinical malaria.

CONCLUSIONS

These results lend support for the development of conserved regions of EBA-175 as components in a combination of a malaria vaccine.

Monocyte- and Neutrophil-Derived CXCL10 Impairs Efficient Control of Blood-Stage Malaria Infection and Promotes Severe Disease

CXCL10, or IFN-γ-inducible protein 10, is a biomarker associated with increased risk for Plasmodium falciparum-mediated cerebral malaria (CM). Consistent with this, we have previously shown that CXCL10 neutralization or genetic deletion alleviates brain intravascular inflammation and protects Plasmodium berghei ANKA-infected mice from CM. In addition to organ-specific effects, the absence of CXCL10 during infection was also found to reduce parasite biomass. To identify the cellular sources of CXCL10 responsible for these processes, we irradiated and reconstituted wild-type (WT) and CXCL10(-/-) mice with bone marrow from either WT or CXCL10(-/-) mice. Similar to CXCL10(-/-) mice, chimeras unable to express CXCL10 in hematopoietic-derived cells controlled infection more efficiently than WT controls. In contrast, expression of CXCL10 in knockout mice reconstituted with WT bone marrow resulted in high parasite biomass levels, higher brain parasite and leukocyte sequestration rates, and increased susceptibility to CM. Neutrophils and inflammatory monocytes were identified as the main cellular sources of CXCL10 responsible for the induction of these processes. The improved control of parasitemia observed in the absence of CXCL10-mediated trafficking was associated with a preferential accumulation of CXCR3(+)CD4(+) T follicular helper cells in the spleen and enhanced Ab responses to infection. These results are consistent with the notion that some inflammatory responses elicited in response to malaria infection contribute to the development of high parasite densities involved in the induction of severe disease in target organs.

A potential role for interleukin-33 and γ-epithelium sodium channel in the pathogenesis of human malaria associated lung injury

Background

The pathogenesis of pulmonary oedema (PE) in patients with severe malaria is still unclear. It has been hypothesized that lung injury depends, in addition to microvascular obstruction, on an increased pulmonary capillary pressure and altered alveolar-capillary membrane permeability, causing pulmonary fluid accumulation.

Methods

This study compared the histopathological features of lung injury in Southeast Asian patients (n = 43) who died from severe Plasmodium falciparum malaria, and correlated these with clinical history in groups with or without PE. To investigate the expression of mediators that may influence fluid accumulation in PE, immunohistochemistry and image analysis were performed on controls and sub-sets of patient with or without PE.

Results

The expression of leukocyte sub-set antigens, bronchial interleukin (IL)-33, γ-epithelium sodium channel (ENaC), aquaporin (AQP)-1 and -5, and control cytokeratin staining was quantified in the lung tissue of severe malaria patients. Bronchial IL-33 expression was significantly increased in severe malaria patients with PE. Malaria patients with shock showed significantly increased bronchial IL-33 compare to other clinical manifestations. Bronchial IL-33 levels were positively correlated with CD68+ monocyte and elastase + neutrophil, septal congestion and hyaline membrane formation. Moreover, the expression of both vascular smooth muscle cell (VSMC) and bronchial γ-ENaC significantly decreased in severe malaria patients with PE. Both VSMC and bronchial γ-ENaC were negatively correlated with the degree of parasitized erythrocyte sequestration, alveolar thickness, alveolar expansion score, septal congestion score, and malarial pigment score. In contrast AQP-1 and -5 and pan cytokeratin levels were similar between groups.

Conclusions

The results suggest that IL-33 may play a role in lung injury during severe malaria and lead to PE. Both VSMC and bronchial γ-ENaC downregulation may explain pulmonary fluid disturbances and participate in PE pathogenesis in severe malaria patients.

Ultrasonographic assessment of splenic volume at presentation and after anti-malarial therapy in children with malarial anaemia

Background

Splenic enlargement is a component of the host response to malaria and may also influence the genesis and progression of malarial anaemia. Few cross-sectional and no longitudinal studies have assessed the relationship between splenic volume measured ultrasonographically and haemoglobin concentrations in children with malaria.

Methods

Fifteen Papua New Guinean children with severe malarial anaemia (SMA; haemoglobin <50 g/L) and ten with moderate malarial anaemia (MMA; 51–99 g/L) were recruited. The SMA patients were given intramuscular artemether followed by oral artemisinin combination therapy (ACT), and were transfused one unit of packed cells 0.3-4.0 days post-admission. The MMA patients were treated with ACT. Splenic enlargement (Hackett’s grade, subcostal distance and ultrasonographically determined volume) and haemoglobin concentrations were measured on days 0, 1, 2, 3, 7, 14, 28, and 42.

Results

Associations between Hackett’s grade, subcostal distance and splenic volume were modest (r_s ≤ 0.62, P <0.001). Baseline splenic volume was not associated with age or haemoglobin (P ≥0.90). Mean splenic volume had fallen by approximately 50 % at day 14 in children with MMA (P ≤0.011 vs days 0, 1 and 2), but there was no change in the SMA group (P ≥0.30). There was no change in haemoglobin in the MMA group during follow-up but a rise in the SMA group to day 7 (P ≤0.05 vs days 0, 1, 2, and 3) which paralleled the packed cell volume transfused.

Conclusions

Clinical assessment of splenomegaly is imprecise compared with ultrasonography. Serial splenic volumes and haemoglobin concentrations suggest that the spleen does not influence post-treatment haemoglobin, including after transfusion.

Antibodies to the Plasmodium falciparum Proteins MSPDBL1 and MSPDBL2 Opsonize Merozoites, Inhibit Parasite Growth, and Predict Protection From Clinical Malaria

Increasing evidence suggests that antibodies against merozoite surface proteins (MSPs) play an important role in clinical immunity to malaria. Two unusual members of the MSP-3 family, merozoite surface protein duffy binding-like (MSPDBL)1 and MSPDBL2, have been shown to be extrinsically associated to MSP-1 on the parasite surface. In addition to a secreted polymorphic antigen associated with merozoite (SPAM) domain characteristic of MSP-3 family members, they also contain Duffy binding-like (DBL) domain and were found to bind to erythrocytes, suggesting that they play a role in parasite invasion. Antibody responses to these proteins were investigated in a treatment-reinfection study conducted in an endemic area of Papua New Guinea to determine their contribution to naturally acquired immunity. Antibodies to the SPAM domains of MSPDBL1 and MSPDBL2 as well as the DBL domain of MSPDBL1 were found to be associated with protection from Plasmodium falciparum clinical episodes. Moreover, affinity-purified anti-MSPDBL1 and MSPDBL2 were found to inhibit in vitro parasite growth and had strong merozoite opsonizing capacity, suggesting that protection targeting these antigens results from ≥2 distinct effector mechanisms. Together these results indicate that MSPDBL1 and MSPDBL2 are important targets of naturally acquired immunity and might constitute potential vaccine candidates.

In vivo antimalarial activity and toxicological effects of methanolic extract of Cocos nucifera (Dwarf red variety) husk fibre

OBJECTIVE

Phytochemical constituents as well as antimalarial and toxicity potentials of the methanolic extract of the husk fibre of Dwarf Red variety of Cocos nucifera were evaluated in this study.

METHODS

The dried powdered husk fibre was exhaustively extracted with hexane, ethyl acetate and methanol successively and the methanolic extract was screened for flavonoids, phenolics, tannins, alkaloids, steroids, triterpenes, phlobatannins, anthraquinones and glycosides. A 4-day suppressive antimalarial test was carried out using Plasmodium berghei NK65-infected mice, to which the extract was administered at doses of 31.25, 62.5, 125, 250 and 500 mg/kg body weight (BW). Toxicity of the extract was evaluated in rats using selected hematological parameters and organ function indices after orally administering doses of 25, 50 and 100 mg/kg BW for 14 d.

RESULTS

Phytochemical analysis revealed the presence of alkaloids, tannins, phenolics, saponins, glycosides, steroids and anthraquinones in the extract. Moreover, the extract reduced parasitemia by 39.2% and 45.8% at doses of 250 and 500 mg/kg BW respectively on day 8 post-inoculation. Various hematological parameters evaluated were not significantly altered (P>0.05) at all doses of the extract, except red blood cell count which was significantly elevated (P<0.05) at 100 mg/kg BW. The extract significantly increased (P<0.05) urea, creatinine, cholesterol, high-density lipoprotein-cholesterol and bilirubin concentrations in the serum as well as atherogenic index, while it reduced albumin concentration significantly (P<0.05) at higher doses compared to the controls. Alanine aminotransferase activity was reduced in the liver and heart significantly (P<0.05) but was increased in the serum significantly (P<0.05) at higher doses of the extract compared to the controls.

CONCLUSION

The results suggest that methanolic extract of the Dwarf red variety has partial antimalarial activity at higher doses, but is capable of impairing normal kidney and liver function as well as predisposing subjects to cardiovascular diseases.

Fatal cerebral malaria: a venous efflux problem

Most Plasmodium falciparum-infected children with cerebral malaria (CM) die from respiratory arrest, but the underlying pathology is unclear. Here we present a model in which the ultimate cause of death from CM is severe intracranial hypertension. Dynamic imaging of mice infected with P. berghei ANKA, an accepted model for experimental CM, revealed that leukocyte adhesion impairs the venous blood flow by reducing the functional lumen of postcapillary venules (PCV). The resulting increase in intracranial pressure (ICP) exacerbates cerebral edema formation, a hallmark of both murine and pediatric CM. We propose that two entirely different pathogenetic mechanisms-cytoadherence of P. falciparum-infected erythrocytes in pediatric CM and leukocyte arrest in murine CM-result in the same pathological outcome: a severe increase in ICP leading to brainstem herniation and death from respiratory arrest. The intracranial hypertension (IH) model unifies previous hypotheses, applies to human and experimental CM alike, eliminates the need to explain any selective recognition mechanism Plasmodium might use to target multiple sensitive sites in the brain, and explains how an intravascular parasite can cause so much neuronal dysfunction.

Malaria, schistosomiasis and soil transmitted helminth burden and their correlation with anemia in children attending primary schools in Kinshasa, Democratic Republic of Congo

Background

Anaemia reduces cognitive potential in school children, retards their growth and predisposes them to other diseases. As there is a paucity of data on the current burden of P. falciparum, S. mansoni and soil transmitted helminths (STH) infections and their correlation with schoolchildren’s anemia in the Democratic Republic of Congo (DRC), we collect these data.

Methods

This study reports baseline data collected from a randomized controlled trial investigating the impact of IPT with SP and SP-PQ on anemia and malaria morbidity in Congolese schoolchildren (Trial registration: NCT01722539; PACTR201211000449323). S. mansoni and STH infections were assessed using kato-katz technique. Malaria infection and hemoglobin concentration were assessed using Blood smear and Hemocontrol device, respectively.

Results

A total of 616 primary schoolchildren from 4 to 13 years old were enrolled in the study. The prevalence of Plasmodium spp. infection was 18.5% (95%CI:15.6–21.9). Amongst those infected, 24 (21%), 40 (35.1%), 40 (35.1%), 10 (8.8%), had light, moderate, heavy, very high malaria parasite density, respectively. Above 9 years of age (p = 0.02), male and history of fever (p = 0.04) were both associated with malaria infection. The overall prevalence of S. mansoni infection was 6.4% (95%CI:4.4–9.1). Girls were associated with S. mansoni infection (p = 0.04). T. trichiura was the most prevalent STH infection (26.3%), followed by A. lumbricoides (20.1%). Co-infection with malaria-S. mansoni and malaria-STH was, respectively, 1.5% (CI_95%:0.7–3.3) and 6.4% (CI_95% 4.4–9.1). The prevalence of anemia was found to be 41.6% (95%CI:37.7–45.6) and anemia was strongly related with Plasmodium ssp infection (aOR:4.1; CI95%:2.6–6.5;p<0.001) and S. mansoni infection (aOR:3.3;CI95%:1.4–7.8;p<0.01).

Conclusion

Malaria and S. mansoni infection were strongly associated with high prevalence of anemia in schoolchildren. Therefore, specific school-based interventions, such as intermittent preventive treatment or prophylaxis, LLITN distribution, anthelminthic mass treatment and micronutrient supplementation are needed to improve school children’s health.

Determining parameter distribution in within-host severe P. falciparum malaria

Numerous studies have been carried out on within-host Plasmodium falciparum malaria with varying results. Some studies have suggested over estimation of parasite growth within an infected host while others stated that evolution of parasitaemia seems to be quelled by parasite load. Various mathematical models have been designed to understand the dynamics of evolution of within-host malaria. The basic ingredient in most of the models is that the availability of uninfected red blood cells (RBCs) in which the parasite develops is a limiting factor in the propagation of the parasite population. We hypothesize that in severe malaria, due to parasite quest for survival and rapid multiplication, the vicious malaria parasite is sophisticated and can be absorbed in an already infected RBC and speeds up rapture rate. The study reviews the classical models of blood stage malaria and proposes a new model which incorporates double infection. Analysis of the model and parameter identifiability using Markov chain Monte Carlo (MCMC) are presented. MCMC uses distribution of parameters to study the model behavior instead of single points. Results indicate that most infected RBCs rupture quickly due to the disease instead. This may explain anemia in malaria patients and lack of uniformity of oscillations in within-host malaria. Therefore, more needs to be done as far as within-host malaria is concerned, to provide step by step evolution of malaria within a host.

Maladjusted host immune responses induce experimental cerebral malaria-like pathology in a murine Borrelia and Plasmodium co-infection model

In the Plasmodium infected host, a balance between pro- and anti-inflammatory responses is required to clear the parasites without inducing major host pathology. Clinical reports suggest that bacterial infection in conjunction with malaria aggravates disease and raises both mortality and morbidity in these patients. In this study, we investigated the immune responses in BALB/c mice, co-infected with Plasmodium berghei NK65 parasites and the relapsing fever bacterium Borrelia duttonii. In contrast to single infections, we identified in the co-infected mice a reduction of L-Arginine levels in the serum. It indicated diminished bioavailability of NO, which argued for a dysfunctional endothelium. Consistent with this, we observed increased sequestration of CD8+ cells in the brain as well over expression of ICAM-1 and VCAM by brain endothelial cells. Co-infected mice further showed an increased inflammatory response through IL-1β and TNF-α, as well as inability to down regulate the same through IL-10. In addition we found loss of synchronicity of pro- and anti-inflammatory signals seen in dendritic cells and macrophages, as well as increased numbers of regulatory T-cells. Our study shows that a situation mimicking experimental cerebral malaria (ECM) is induced in co-infected mice due to loss of timing and control over regulatory mechanisms in antigen presenting cells.

The contribution of natural killer complex loci to the development of experimental cerebral malaria

Background

The Natural Killer Complex (NKC) is a genetic region of highly linked genes encoding several receptors involved in the control of NK cell function. The NKC is highly polymorphic and allelic variability of various NKC loci has been demonstrated in inbred mice, providing evidence for NKC haplotypes. Using BALB.B6-Cmv1^r congenic mice, in which NKC genes from C57BL/6 mice were introduced into the BALB/c background, we have previously shown that the NKC is a genetic determinant of malarial pathogenesis. C57BL/6 alleles are associated with increased disease-susceptibility as BALB.B6-Cmv1^r congenic mice had increased cerebral pathology and death rates during P. berghei ANKA infection than cerebral malaria-resistant BALB/c controls.

Methods

To investigate which regions of the NKC are involved in susceptibility to experimental cerebral malaria (ECM), intra-NKC congenic mice generated by backcrossing recombinant F2 progeny from a (BALB/c x BALB.B6-Cmv1^r) F1 intercross to BALB/c mice were infected with P. berghei ANKA.

Results

Our results revealed that C57BL/6 alleles at two locations in the NKC contribute to the development of ECM. The increased severity to severe disease in intra-NKC congenic mice was not associated with higher parasite burdens but correlated with a significantly enhanced systemic IFN-γ response to infection and an increased recruitment of CD8⁺ T cells to the brain of infected animals.

Conclusions

Polymorphisms within the NKC modulate malarial pathogenesis and acquired immune responses to infection.

Immunobiology of Plasmodium in liver and brain

Malaria remains one of the most serious health problems globally, but our understanding of the biology of the parasite and the pathogenesis of severe disease is still limited. Multiple cellular effector mechanisms that mediate parasite elimination from the liver have been described, but how effector cells use classical granule-mediated cytotoxicity to attack infected hepatocytes and how cytokines and chemokines spread via the unique fluid pathways of the liver to reach the parasites over considerable distances remains unknown. Similarly, a wealth of information on cerebral malaria (CM), one of the most severe manifestations of the disease, was gained from post-mortem analyses of human brain and murine disease models, but the cellular processes that ultimately cause disease are not fully understood. Here, we discuss how imaging of the local dynamics of parasite infection and host response as well as consideration of anatomical and physiological features of liver and brain can provide a better understanding of the initial asymptomatic hepatic phase of the infection and the cascade of events leading to CM. Given the increasing drug resistance of both parasite and vector and the unavailability of a protective vaccine, the urgency to reduce the tremendous morbidity and mortality associated with severe malaria is obvious.

The role of chemokines in severe malaria: more than meets the eye

Plasmodium falciparum malaria is responsible for over 250 million clinical cases every year worldwide. Severe malaria cases might present with a range of disease syndromes including acute respiratory distress, metabolic acidosis, hypoglycaemia, renal failure, anaemia, pulmonary oedema, cerebral malaria (CM) and placental malaria (PM) in pregnant women. Two main determinants of severe malaria have been identified: sequestration of parasitized red blood cells and strong pro-inflammatory responses. Increasing evidence from human studies and malaria infection animal models revealed the presence of host leucocytes at the site of parasite sequestration in brain blood vessels as well as placental tissue in complicated malaria cases. These observations suggested that apart from secreting cytokines, leucocytes might also contribute to disease by migrating to the site of parasite sequestration thereby exacerbating organ-specific inflammation. This evidence attracted substantial interest in identifying trafficking pathways by which inflammatory leucocytes are recruited to target organs during severe malaria syndromes. Chemo-attractant cytokines or chemokines are the key regulators of leucocyte trafficking and their potential contribution to disease has recently received considerable attention. This review summarizes the main findings to date, investigating the role of chemokines in severe malaria and the implication of these responses for the induction of pathogenesis and immunity to infection.

Advances in nanomedicines for malaria treatment

Malaria is an infectious disease that mainly affects children and pregnant women from tropical countries. The mortality rate of people infected with malaria per year is enormous and became a public health concern. The main factor that has contributed to the success of malaria proliferation is the increased number of drug resistant parasites. To counteract this trend, research has been done in nanotechnology and nanomedicine, for the development of new biocompatible systems capable of incorporating drugs, lowering the resistance progress, contributing for diagnosis, control and treatment of malaria by target delivery. In this review, we discussed the main problems associated with the spread of malaria and the most recent developments in nanomedicine for anti-malarial drug delivery.

Neuroimmunological blood brain barrier opening in experimental cerebral malaria

Plasmodium falciparum malaria is responsible for nearly one million annual deaths worldwide. Because of the difficulty in monitoring the pathogenesis of cerebral malaria in humans, we conducted a study in various mouse models to better understand disease progression in experimental cerebral malaria (ECM). We compared the effect on the integrity of the blood brain barrier (BBB) and the histopathology of the brain of P. berghei ANKA, a known ECM model, P. berghei NK65, generally thought not to induce ECM, P. yoelii 17XL, originally reported to induce human cerebral malaria-like histopathology, and P. yoelii YM. As expected, P. berghei ANKA infection caused neurological signs, cerebral hemorrhages, and BBB dysfunction in CBA/CaJ and Swiss Webster mice, while Balb/c and A/J mice were resistant. Surprisingly, PbNK induced ECM in CBA/CaJ mice, while all other mice were resistant. P. yoelii 17XL and P. yoelii YM caused lethal hyperparasitemia in all mouse strains; histopathological alterations, BBB dysfunction, or neurological signs were not observed. Intravital imaging revealed that infected erythrocytes containing mature parasites passed slowly through capillaries making intimate contact with the endothelium, but did not arrest. Except for relatively rare microhemorrhages, mice with ECM presented no obvious histopathological alterations that would explain the widespread disruption of the BBB. Intravital imaging did reveal, however, that postcapillary venules, but not capillaries or arterioles, from mice with ECM, but not hyperparasitemia, exhibit platelet marginalization, extravascular fibrin deposition, CD14 expression, and extensive vascular leakage. Blockage of LFA-1 mediated cellular interactions prevented leukocyte adhesion, vascular leakage, neurological signs, and death from ECM. The endothelial barrier-stabilizing mediators imatinib and FTY720 inhibited vascular leakage and neurological signs and prolonged survival to ECM. Thus, it appears that neurological signs and coma in ECM are due to regulated opening of paracellular-junctional and transcellular-vesicular fluid transport pathways at the neuroimmunological BBB.

Plasmodium falciparum, the deadliest of all human malaria parasites, can cause cerebral malaria, a severe and frequently fatal complication of this devastating disease. Young children are predominantly at risk and may progress rapidly from the first signs of neurological involvement to coma and death. Here we used a murine model for high-resolution in vivo imaging to demonstrate that cerebral malaria, but not high parasitemia and severe anemia, is associated with extensive leakage of fluid from cerebral blood vessels into the brain tissue. This vascular leakage occurs downstream from the capillary bed, at the neuroimmunological blood brain barrier, a site recently recognized as the immune cell entry point into the brain during neuroinflammation. Vascular leakage is closely associated with the appearance of neurological signs suggesting that the ultimate cause of brain edema, coma and death in cerebral malaria is a widespread opening of the neuroimmunological blood brain barrier. Indeed, vascular leakage, neurological signs, and death from ECM can be prevented with endothelial barrier-stabilizing drugs. Based on the unique role of this anatomical feature in neuroinflammation, our findings are expected to have implications for other infectious diseases and autoimmune disorders of the central nervous system.

The prognostic value of schizontaemia in imported Plasmodium falciparum malaria

Background

In Plasmodium falciparum infection, peripheral parasite counts do not always correlate well with the sequestered parasite burden. As erythrocytes parasitized with mature trophozoites and schizonts have a high tendency to adhere to the microvascular endothelium, they are often absent in peripheral blood samples. The appearance of schizonts in peripheral blood smears is thought to be a marker of high sequestered parasite burden and severe disease. In the present study, the value of schizontaemia as an early marker for severe disease in non-immune individuals with imported malaria was evaluated.

Methods

All patients in the Rotterdam Malaria Cohort diagnosed with P. falciparum malaria between 1 January 1999 and 1 January 2012 were included. Thick and thin blood films were examined for the presence of schizontaemia. The occurrence of WHO defined severe malaria was the primary endpoint. The diagnostic performance of schizontaemia was compared with previously evaluated biomarkers C-reactive protein and lactate.

Results

Schizonts were present on admission in 49 of 401 (12.2%) patients. Patients with schizontaemia were more likely to present with severe malaria, a more complicated course and had longer duration of admission in hospital. Schizontaemia had a specificity of 0.95, a sensitivity of 0.53, a negative predictive value of 0.92 and a positive predictive value of 0.67 for severe malaria. The presence of schizonts was an independent predictor for severe malaria.

Conclusion

Absence of schizonts was found to be a specific marker for exclusion of severe malaria. Presence of schizonts on admission was associated with a high positive predictive value for severe malaria. This may be of help to identify patients who are at risk of a more severe course than would be expected when considering peripheral parasitaemia alone.

Role of polymorphisms of toll-like receptor (TLR) 4, TLR9, toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) and FCGR2A genes in malaria susceptibility and severity in Burundian children

Background

Malaria caused by Plasmodium falciparum is one of the leading causes of human morbidity and mortality from infectious diseases, predominantly in tropical and sub-tropical countries. As genetic variations in the toll-like receptors (TLRs)-signalling pathway have been associated with either susceptibility or resistance to several infectious and inflammatory diseases, the supposition is that single nucleotide polymorphisms (SNPs) of TLR2, TLR4, TLR9, Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) and FCGR2A could modulate malaria susceptibility and severity.

Methods

This study was planned to make a further contribution to solving the problem of the real role of the most common polymorphisms of TLR4, TLR9, TIRAP and FCGR2A genes in modulating the risk of malaria and disease severity in children from Burundi, Central Africa. All the paediatric patients aged six months to 10 years admitted to the hospital of Kiremba, Burundi, between February 2011 and September 2011, for fever and suspicion of acute malaria were screened for malaria parasitaemia by light microscopy of thick and thin blood smears. In children with malaria and in uninfected controls enrolled during the study period in the same hospital, blood samples were obtained on filter paper and TLR4 Asp299Gly rs4986790, TLR9 G1174A rs352139, T-1486 C rs187084 TLR9 T-1237 C rs5743836, TIRAP Ser180Leu rs8177374 and the FCGR2A His131Arg rs1801274 polymorphisms were studied using an ABI PRISM 7900 HT Fast Real-time instrument.

Results

A total of 602 patients and 337 controls were enrolled. Among the malaria cases, 553 (91.9 %) were considered as suffering from uncomplicated and 49 (8.1 %) from severe malaria. TLR9 T1237C rs5743836CC was associated with an increased risk of developing malaria (p = 0.03), although it was found with the same frequency in uncomplicated and severe malaria cases. No other differences were found in all alleles studied and in genotype frequencies between malaria cases and uninfected controls as well as between uncomplicated and severe malaria cases.

Conclusions

TLR9 T1237C seems to condition susceptibility to malaria in Burundian children but not its severity, whereas none of the assessed SNPs of TLR4, TIRAP and FCGR2A seem to influence susceptibility to malaria and disease severity in this population.

Seasonal variation of malaria parasite density in paediatric population of Northeastern Nigeria

Malaria is a major cause of morbidity and mortality in children and adults in the Sudano Sahel of Northeastern Nigeria with the highest prevalence of malaria in pregnancy of 64.5 in Nigeria recorded in this region. This study was carried out in 2003 and 2004 to provide parasitological baseline data for the development of Malaria Early Warning System (MEWS) for the surveillance of type I epidemic caused by meteorological conditions and to provide data for timing malaria key vector control measures such as Indoor Residual Spraying (IRS) for maximum effect. Clinical information about malaria cases were used in this study. In all 692 children aged 6 to 96 months were screened for Plasmodium infection and used for the analysis. The results showed that the majority of infected children (68.06%) were aged 12-60 months and their asexual parasite density (ap/ u1) was between 100-500 ap/u1 of the whole blood. The month of September recorded the highest Geometric Mean Asexual-Densities (GMPD) of 13,655 while the lowest parasite densities were observed at the peak of the dry season, especially during the months of March and April. Significance difference (p&lt;0.05) was observed between the sexes in infection rate. It is obvious that male children have higher infection rate (about 67.5%), than while female children (32.5%) regardless of climate seasonality. Designing a malaria early warning system and providing baseline parasitological data for timing of spraying cycles for key malaria vector control measures such as Indoor Residual Spraying (IRS) should be encouraged to complement other effective malaria control strategies .Hence the need for this investigation.

Analysis of var genes cloned from a Plasmodium falciparum isolate in China

OBJECTIVE

To analyse the var gene repertoire and characterise the chondroitin sulphate A (CSA)-binding activity of the Duffy-binding like (DBL) domains encoded by the var2csa gene of a Plasmodium falciparum (P. falciparum) isolate in Hainan Province, China.

METHODS

The sequences of var DBL1 regions were PCR-amplified, sequenced and the sequence characteristics was bioinformatically analysed. Recombinant proteins encoded by the var2csa genes were expressed and purified. The binding activities of the recombinant proteins to CSA receptor was detected by ELISA assays.

RESULTS

Fifty six unique DBL α sequences were obtained, and the sequences represented similar diversity to the var genes of the genome parasite 3D7. There are two var2csa genes in the P. falciparum isolated from Hainan Province. Unlike in other falciparum parasites such as HB3, the two var2csa genes are more diverged. The receptor-binding capacity of DBL-5ε and DBL-6ε domains of HN var2CSA was studied.

CONCLUSIONS

This work represented the diversity of var genes of a P. falciparum isolate in China.

Complement receptor 1 and the molecular pathogenesis of malaria

Malaria is a pathogenic infection caused by protozoa of the genus plasmodium. It is mainly confined to sub-Saharan Africa, Asia and South America. This disease claims the life of over 1.5 to 2.7 million people per year. Owing to such a high incidence of malarial infections, there is an urgent need for the development of suitable vaccines. For the development of ideal vaccines, it is essential to understand the molecular mechanisms of malarial pathogenesis and the factors that lead to malaria infection. Genetic factors have been proposed to play an important role in malarial pathogenesis. Complement receptor 1 (CR1) is an important host red blood cell protein involved in interaction with malarial parasite. Various polymorphic forms of CR1 have been found to be involved in conferring protection or increasing susceptibility to malaria infections. Low-density allele (L) of CR1 gave contradictory results in different set of studies. In addition, Knops polymorphic forms Sl (a⁺) and McC (a) have been found to contribute more towards the occurrence of cerebral malaria in malaria endemic regions compared to individuals with Sl (a^-) / McC (a/b) genotype. This article reviews the research currently going on in this area and throws light on as yet unresolved mysteries of the role of CR1 in malarial pathogenesis

ABO research in the modern era of genomics

Research on ABO has advanced significantly in recent years. A database was established to manage the sequence information of an increasing number of novel alleles. Genome sequencings have identified ABO orthologues and paralogues in various organisms and enhanced the knowledge on the evolution of the ABO and related genes. The most prominent advancements include clarification of the association between ABO and different disease processes. For instance, ABO status affects the infectivity of certain strains of Helicobacter pylori and Noroviruses as well as the sequestration and rosetting of red blood cells infected with Plasmodium falciparum. Genome-wide association studies have conclusively linked the ABO locus to pancreatic cancer, venous thromboembolism, and myocardial infarction in the presence of coronary atherosclerosis. These findings suggest ABO's important role in determining an individual's susceptibility to such diseases. Furthermore, our understanding of the structures of A and B transferases and their enzymology has been dramatically improved. ABO has also become a research subject in neurobiology and the preparation of artificial/universal blood and became a topic in the pseudoscience of "blood type diets." With such new progress, it has become evident that ABO is a critical player in the modern era of genomic medicine. This article provides the most up-to-date information regarding ABO genomics.