Severity of retinopathy parallels the degree of parasite sequestration in the eyes and brains of malawian children with fatal cerebral malaria

From Bench to Bedside: Unraveling Cerebral Malaria and Malarial Retinopathy by Combining Clinical and Pre-Clinical Perspectives

Infection with Plasmodium falciparum carries a significant risk of cerebral malaria (CM). Children are particularly susceptible to human CM (HCM) which manifests as an acute neurovascular encephalopathy leading to high levels of mortality. Occurring in parallel with CM, malarial retinopathy (MR) is readily detected on ophthalmoscopy as one or more of: white-centered retinal hemorrhage, retinal whitening, and vessel discoloration. It leads to several distinct types of blood retinal barrier (BRB) breakdown. The precise molecular mechanisms underpinning CM and MR remain ill-defined, but parasitemia is known to drive progressive neurovascular obstruction and inflammation leading to cerebral and retinal edema and ischemia. Extensive clinical studies in patients with CM have shown that retinal examination is a useful approach for understanding pathology and an indicator for risk of mortality and morbidity. Fully understanding the cellular and molecular mechanisms that underpin CM and MR is important for developing new therapeutic approaches and in this regard the murine model of experimental CM (ECM) has proved to offer considerable value. Much is known about brain pathology in this model although much less is understood about the retina. In this review, we seek to evaluate MR in clinical scenarios and make comparisons with the retina from mice with ECM. Through detailed in vivo and post-mortem studies in the mouse and human retina, this review highlights the links between CM and MR and how this will aid our understanding of the disease progression and pathogenesis.

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.

Severe malaria intervention status in Nigeria: workshop meeting report

Nigeria accounts for 39% of global malaria deaths in children under 5 years of age and the effective management of severe malaria is a health priority. The Annual Nigeria Severe Malaria Stakeholders Workshop, held on the 5-6th of July 2023 in Abuja, Nigeria brought together representatives from 36 States, the Federal Capital Territory, and other key stakeholders to address the management of severe malaria across all levels of the health service. Aims were to provide updates and review progress on severe malaria activities, the burden of disease, commodity logistics management, and pre-referral national policy implementation as well as to disseminate research findings. Two roundtable discussions were conducted to identify the challenges, barriers, and facilitators to the effective management of severe malaria in Nigeria. A key challenge was the limited awareness of updated guidelines and strategic documents among frontline health workers, leading to the misuse of non-recommended medications, like α-β-arteether. Further to this, the need to ensure appropriate treatments during pregnancy and the adoption of the WHO directive on the use of rectal artesunate were highlighted. To address these issues, innovative dissemination channels for guideline awareness were recommended and collaboration with professional organizations to enrich training materials emphasized. Other areas for improvement considered the processes involved in severe malaria management, with insufficient coordination among government agencies, inadequate referral linkages, and inadequate human resources identified as barriers. Recommendations focused on practical measures to minimize wastage of injectable artesunate, enhance data management through scaling up electronic medical records, and strengthen referral systems. The extension of severe malaria surveillance to patients older than 5 years was also proposed. To deliver these changes, actionable plans for sustained recruitment and training are needed, as well as committed advocacy at all levels to ensure timely fund disbursement and institutional support. A key overarching theme from the workshop was that a multifaceted approach was needed to address severe malaria in Nigeria, emphasizing collaborative efforts, evidence-based practices, and strategic resource allocation. With the largest malaria burden globally, the potential impact of addressing the challenges of severe malaria management in Nigeria cannot be understated and must be urgently addressed.

Clinical aspects of malarial retinopathy: a critical review

This review will provide a better understanding of a set of signs known as malarial retinopathy. The discovery of this retinopathy in association with cerebral malaria is important because it best distinguishes patients with true cerebral malaria from those with coma due to other causes and incidental Plasmodium falciparum parasitemia. Identifying a comatose patient with malarial retinopathy increases the likelihood of an accurate severe or cerebral malaria diagnosis. As the World Health Organization does not specify that malarial retinopathy is one of the factors included in determining a cerebral malaria diagnosis, there are significant false-positive diagnoses of cerebral malaria. Once a cerebral malaria diagnosis is assigned, other possibilities and treatments are often excluded making an incorrect diagnosis of cerebral malaria potentially fatal. However, Plasmodium falciparum may also contribute to coma in some children with retinopathy-negative cerebral malaria, as this group is still not clinically well characterized, so all children with the WHO definition of cerebral malaria should be treated for severe malaria. Nevertheless, by raising awareness about malarial retinopathy, there could be a greater potential to accurately diagnose cerebral malaria and thus achieve more positive patient outcomes in the future. This literary review aims to raise awareness of the retinopathy by defining what it is to non-experts, explaining its pathology, clarifying the techniques needed to accurately diagnose malarial retinopathy, as well as the barriers that prevent clinicians from providing a proper diagnosis in malaria-endemic regions; and finally, discuss future directions to continue the study of malarial retinopathy.

Cerebrospinal fluid biomarkers provide evidence for kidney-brain axis involvement in cerebral malaria pathogenesis

Introduction

Cerebral malaria is one of the most severe manifestations of malaria and is a leading cause of acquired neurodisability in African children. Recent studies suggest acute kidney injury (AKI) is a risk factor for brain injury in cerebral malaria. The present study evaluates potential mechanisms of brain injury in cerebral malaria by evaluating changes in cerebrospinal fluid measures of brain injury with respect to severe malaria complications. Specifically, we attempt to delineate mechanisms of injury focusing on blood-brain-barrier integrity and acute metabolic changes that may underlie kidney-brain crosstalk in severe malaria.

Methods

We evaluated 30 cerebrospinal fluid (CSF) markers of inflammation, oxidative stress, and brain injury in 168 Ugandan children aged 18 months to 12 years hospitalized with cerebral malaria. Eligible children were infected with Plasmodium falciparum and had unexplained coma. Acute kidney injury (AKI) on admission was defined using the Kidney Disease: Improving Global Outcomes criteria. We further evaluated blood-brain-barrier integrity and malaria retinopathy, and electrolyte and metabolic complications in serum.

Results

The mean age of children was 3.8 years (SD, 1.9) and 40.5% were female. The prevalence of AKI was 46.3% and multi-organ dysfunction was common with 76.2% of children having at least one organ system affected in addition to coma. AKI and elevated blood urea nitrogen, but not other measures of disease severity (severe coma, seizures, jaundice, acidosis), were associated with increases in CSF markers of impaired blood-brain-barrier function, neuronal injury (neuron-specific enolase, tau), excitatory neurotransmission (kynurenine), as well as altered nitric oxide bioavailability and oxidative stress (p < 0.05 after adjustment for multiple testing). Further evaluation of potential mechanisms suggested that AKI may mediate or be associated with CSF changes through blood-brain-barrier disruption (p = 0.0014), ischemic injury seen by indirect ophthalmoscopy (p < 0.05), altered osmolality (p = 0.0006) and through alterations in the amino acids transported into the brain.

Conclusion

In children with cerebral malaria, there is evidence of kidney-brain injury with multiple potential pathways identified. These changes were specific to the kidney and not observed in the context of other clinical complications.

Using Malarial Retinopathy to Improve the Diagnosis of Pediatric Cerebral Malaria

In malaria endemic areas, a high proportion of children have detectable parasitemia but show no clinical symptoms. When comatose from a cause other than malaria, this group confounds the cerebral malaria (CM) definition, making accurate diagnosis challenging. One important biomarker of CM is malarial retinopathy, a set of specific features visible in the ocular fundus. In this study, we quantified the contribution of malarial retinopathy in discriminating malaria-caused coma from non-malaria-caused coma. We estimated that 10% of our study cohort of N = 1,192 patients who met the WHO clinical definition of CM in Malawi had non-malarial coma based on a Gaussian mixture model using the parasite protein Plasmodium falciparum histidine-rich protein-2. A classification based on platelets, white blood cells, and retinopathy significantly improved the discriminative power of a previously established model including only platelets plus white blood cells (area under the receiver operating characteristic curve: 0.89 versus 0.75, P value < 0.001). We conclude that malarial retinopathy is highly predictive of malaria-caused versus non-malaria-caused coma and recommend that an ocular funduscopic examination to determine malarial retinopathy status be included in the assessment of parasitemic comatose African children.

Measuring the Impact of Malaria on the Living Human Retina

Retinal examination and imaging are relatively simple methods for studying the dynamic impact of cerebral malaria on the microcirculation of the central nervous system. Retina and brain are affected similarly by Plasmodium falciparum. Unlike the brain, the human retina can be directly observed using commercially available clinical instruments in the setting of a critical care unit, and this can be done repeatedly and non-invasively. Additional information about blood-tissue barriers can be gained from fluorescein angiography. Non-ophthalmologist clinician scientists are usually unfamiliar with ophthalmoscopy and retinal imaging, and some readers may feel that these techniques are beyond them. This chapter aims to quell these fears by providing a step-by-step description of how to examine and photograph the human retina in children with cerebral malaria.

Ocular Pathology of Cerebral Malaria

Investigation of post-mortem eyes from children with malarial retinopathy has helped to explain the retinal pathology of cerebral malaria, and also demonstrated histological associations between evolving retinal pathogenesis-visible clinically-and similar cerebral features which can only be examined at autopsy. The pathology of malarial retinopathy has been well-described and correlates with brain pathology. Some clinical and pathological features are associated with outcome. This chapter describes the materials and methods needed to study the pathological features of malarial retinopathy. Some are common to histopathology in general, but accurate spatial correlation between retinal features observed in life and their associated pathology in post-mortem specimens requires special techniques.

Cerebral malaria: insight into pathology from optical coherence tomography

We aimed to investigate structural retinal changes in malarial retinopathy (MR) using hand-held optical coherence tomography (HH-OCT) to assess its diagnostic potential. Children with MR (n = 43) underwent ophthalmoscopy, fluorescein angiography and HH-OCT during admission, 1-month (n = 31) and 1-year (n = 8) post-discharge. Controls were comatose patients without malaria (n = 6) and age/sex-matched healthy children (n = 43). OCT changes and retinal layer thicknesses were compared. On HH-OCT, hyper-reflective areas (HRAs) were seen in the inner retina of 81% of MR patients, corresponding to ischaemic retinal whitening on fundus photography. Cotton wool spots were present in 37% and abnormal hyper-reflective dots, co-localized to capillary plexus, in 93%. Hyper-reflective vessel walls were present in 84%, and intra-retinal cysts in 9%. Vascular changes and cysts resolved within 48 h. HRAs developed into retinal thinning at 1 month (p = 0.027) which was more pronounced after 1 year (p = 0.009). Ischaemic retinal whitening is located within inner retinal layers, distinguishing it from cotton wool spots. Vascular hyper-reflectivity may represent the sequestration of parasitized erythrocytes in vessels, a key CM feature. The mechanisms of post-ischemic retinal atrophy and cerebral atrophy with cognitive impairment may be similar in CM survivors. HH-OCT has the potential for monitoring patients, treatment response and predicting neurological deficits.

Parasite histones are toxic to brain endothelium and link blood barrier breakdown and thrombosis in cerebral malaria

Microvascular thrombosis and blood-brain barrier (BBB) breakdown are key components of cerebral malaria (CM) pathogenesis in African children and are implicated in fatal brain swelling. How Plasmodium falciparum infection causes this endothelial disruption and why this occurs, particularly in the brain, is not fully understood. In this study, we have demonstrated that circulating extracellular histones, equally of host and parasite origin, are significantly elevated in CM patients. Higher histone levels are associated with brain swelling on magnetic resonance imaging. On postmortem brain sections of CM patients, we found that histones are colocalized with P falciparum-infected erythrocytes sequestered inside small blood vessels, suggesting that histones might be expelled locally during parasite schizont rupture. Histone staining on the luminal vascular surface colocalized with thrombosis and leakage, indicating a possible link between endothelial surface accumulation of histones and coagulation activation and BBB breakdown. Supporting this, patient sera or purified P falciparum histones caused disruption of barrier function and were toxic to cultured human brain endothelial cells, which were abrogated with antihistone antibody and nonanticoagulant heparin. Overall, our data support a role for histones of parasite and host origin in thrombosis, BBB breakdown, and brain swelling in CM, processes implicated in the causal pathway to death. Neutralizing histones with agents such as nonanticoagulant heparin warrant exploration to prevent brain swelling in the development or progression of CM and thereby to improve outcomes.

Localised release of matrix metallopeptidase 8 in fatal cerebral malaria

OBJECTIVE

Cerebral malaria (CM) is a complication of Plasmodium falciparum malaria, in which progressive brain swelling is associated with sequestration of parasites and impaired barrier function of the cerebral microvascular endothelium. To test the hypothesis that localised release of matrix metallopeptidase 8 (MMP8) within the retina is implicated in microvascular leak in CM, we examined its expression and association with extravascular fibrinogen leak in a case-control study of post-mortem retinal samples from 13 Malawian children who met the clinical case definition of CM during life. Cases were seven children who were found on post-mortem examination to have 'true-CM' (parasite sequestration in brain blood vessels), whilst controls were six children who had alternative causes of death ('faux-CM', no parasite sequestration in blood vessels).

METHODS

We used immunofluorescence microscopy and independent scoring, by two assessors blinded to the CM status, to assess MMP8 expression, extravascular fibrinogen as an indicator of vascular leak and their co-localisation in the retinal microvasculature.

RESULTS

In 'true-CM' subjects, MMP8 staining was invariably associated with sequestered parasites and a median of 88% (IQR = 74-91%) of capillaries showed MMP8 staining, compared with 14% (IQR = 3.8-24%) in 'faux-CM' (P-value = 0.001). 41% (IQR = 28-49%) of capillaries in 'true-CM' subjects showed co-localisation of extravascular fibrinogen leak and MMP8 staining, compared with 1.8% of capillaries in 'faux-CM' (IQR = 0-3.9%, P-value = 0.01). Vascular leak was rare in the absence of MMP8 staining.

CONCLUSION

Matrix metallopeptidase 8 was extensively expressed in retinal capillaries of Malawian children with malarial retinopathy and strongly associated with vascular leak. Our findings implicate MMP8 as a cause of the vascular endothelial barrier disruption in CM, which may precipitate fatal brain swelling.

How Does Blood-Retinal Barrier Breakdown Relate to Death and Disability in Pediatric Cerebral Malaria?

Background

In cerebral malaria, the retina can be used to understand disease pathogenesis. The mechanisms linking sequestration, brain swelling, and death remain poorly understood. We hypothesized that retinal vascular leakage would be associated with brain swelling.

Methods

We used retinal angiography to study blood-retinal barrier integrity. We analyzed retinal leakage, histopathology, brain magnatic resonance imaging (MRI), and associations with death and neurological disability in prospective cohorts of Malawian children with cerebral malaria.

Results

Three types of retinal leakage were seen: large focal leak (LFL), punctate leak (PL), and vessel leak. The LFL and PL were associated with death (odds ratio [OR] = 13.20, 95% confidence interval [CI] = 5.21–33.78 and OR = 8.58, 95% CI = 2.56–29.08, respectively) and brain swelling (P < .05). Vessel leak and macular nonperfusion were associated with neurological disability (OR = 3.71, 95% CI = 1.26–11.02 and OR = 9.06, 95% CI = 1.79–45.90). Large focal leak was observed as an evolving retinal hemorrhage. A core of fibrinogen and monocytes was found in 39 (93%) white-centered hemorrhages.

Conclusions

Blood-retina barrier breakdown occurs in 3 patterns in cerebral malaria. Associations between LFL, brain swelling, and death suggest that the rapid accumulation of cerebral hemorrhages, with accompanying fluid egress, may cause fatal brain swelling. Vessel leak, from barrier dysfunction, and nonperfusion were not associated with severe brain swelling but with neurological deficits, suggesting hypoxic injury in survivors.

Pathophysiology and neurologic sequelae of cerebral malaria

Cerebral malaria (CM), results from Plasmodium falciparum infection, and has a high mortality rate. CM survivors can retain life-long post CM sequelae, including seizures and neurocognitive deficits profoundly affecting their quality of life. As the Plasmodium parasite does not enter the brain, but resides inside erythrocytes and are confined to the lumen of the brain's vasculature, the neuropathogenesis leading to these neurologic sequelae is unclear and under-investigated. Interestingly, postmortem CM pathology differs in brain regions, such as the appearance of haemorragic punctae in white versus gray matter. Various host and parasite factors contribute to the risk of CM, including exposure at a young age, parasite- and host-related genetics, parasite sequestration and the extent of host inflammatory responses. Thus far, several proposed adjunctive treatments have not been successful in the treatment of CM but are highly needed. The region-specific CM neuro-pathogenesis leading to neurologic sequelae is intriguing, but not sufficiently addressed in research. More attention to this may lead to the development of effective adjunctive treatments to address CM neurologic sequelae.

Mediterranean Diet: Lipids, Inflammation, and Malaria Infection

The Mediterranean diet (MedDiet) consists of consumption of vegetables and healthy oils and have beneficial effects on metabolic and inflammatory diseases. Our goal here is to discuss the role of fatty acid content in MedDiet, mostly omega-3, omega-6, and omega-9 on malaria. Malaria affects millions of people around the globe. The parasite Plasmodium causes the disease. The metabolic and inflammatory alterations in the severe forms have damaging consequences to the host. The lipid content in the MedDiet holds anti-inflammatory and pro-resolutive features in the host and have detrimental effects on the Plasmodium. The lipids from the diet impact the balance of pro- and anti-inflammation, thus, lipids intake from the diet is critical to parasite elimination and host tissue damage caused by an immune response. Herein, we go into the cellular and molecular mechanisms and targets of the MedDiet fatty acids in the host and the parasite, reviewing potential benefits of the MedDiet, on inflammation, malaria infection progression, and clinical outcome.

Plasma cell-free DNA predicts pediatric cerebral malaria severity

BACKGROUNDPrediction of adverse outcomes in cerebral malaria (CM) is difficult. We hypothesized that cell-free DNA (cfDNA) levels would facilitate identification of severe and potentially fatal CM cases.METHODSIn this retrospective study, plasma from Malawian children with CM (n = 134), uncomplicated malaria (UM, n = 77), and healthy controls (HC, n = 60) was assayed for cfDNA using a fluorescence assay. Host and parasite cfDNA was measured by quantitative PCR. Immune markers were determined by ELISA, Luminex, or cytometric bead array.RESULTSTotal cfDNA increased with malaria severity (HC versus UM, P < 0.001; HC versus CM, P < 0.0001; UM versus CM, P < 0.0001), was elevated in retinopathy-positive (Ret+) CM relative to Ret- CM (7.66 versus 5.47 ng/μL, P = 0.027), and differentiated Ret+ fatal cases from survivors (AUC 0.779; P < 0.001). cfDNA levels in patients with non-malarial febrile illness (NMF, P = 0.25) and non-malarial coma (NMC, P = 0.99) were comparable with UM. Host DNA, rather than parasite DNA, was the major cfDNA contributor (UM, 268 versus 67 pg/μL; CM, 2824 versus 463 pg/μL). Host and parasite cfDNA distinguished CM by retinopathy (host, AUC 0.715, P = 0.0001; parasite, AUC 0.745, P = 0.0001), but only host cfDNA distinguished fatal cases (AUC 0.715, P = 0.0001). Total cfDNA correlated with neutrophil markers IL-8 (rs = 0.433, P < 0.0001) and myeloperoxidase (rs = 0.683, P < 0.0001).CONCLUSIONQuantifying plasma cfDNA is a simple assay useful in identifying children at risk for fatal outcome and has promise as a point-of-care assay. Elevated cfDNA suggests a link with host inflammatory pathways in fatal CM.FUNDINGNIH NCATS (AK), Burroughs-Wellcome (AK), and National Health and Medical Research Council of Australia (SJR).

Amount of Brain Edema Correlates With Neurologic Recovery in Pediatric Cerebral Malaria

BACKGROUND

Cerebral malaria (CM) remains a leading cause of mortality and morbidity in children in sub-Saharan Africa. Recent studies using brain magnetic resonance imaging have revealed increased brain volume as a major predictor of death. Similar morphometric predictors of morbidity at discharge are lacking. The aim of this study was to investigate the utility of serial cranial cisternal cerebrospinal fluid (CSF) volume measurements in predicting morbidity at discharge in pediatric CM survivors.

METHODS

In this case-control study, 54 Malawian pediatric CM survivors with neurologic sequelae evident at discharge who underwent serial magnetic resonance imaging scans while comatose were matched to concurrently admitted children with serial imaging who made full recoveries. Serial cranial cisternal CSF volume quantified by radiologists blinded to outcome was evaluated as a predictor of neurologic deficits at discharge. The probability of neurologic sequelae was determined using a model that included coma duration and changes in cisternal CSF volume over time.

RESULTS

Coma duration before admission was similar between cases and controls (16.1 vs. 15.3; P = 0.81), but overall coma was longer among children with sequelae (60 vs. 38 hours; P < 0.01). Lower initial CSF volumes and decreased volumes over time were both associated with a higher probability of neurologic sequelae at discharge.

CONCLUSIONS

Among pediatric CM survivors with prolonged coma, lower initial CSF volume and decreasing volume during coma is associated with neurologic sequelae at discharge. These findings suggest that cerebral edema is an underlying contributor to both morbidity and mortality in pediatric CM.

Cerebral Plasmodium falciparum malaria: The role of PfEMP1 in its pathogenesis and immunity, and PfEMP1-based vaccines to prevent it

Malaria, a mosquito-borne infectious disease caused by parasites of the genus Plasmodium continues to be a major health problem worldwide. The unicellular Plasmodium-parasites have the unique capacity to infect and replicate within host erythrocytes. By expressing variant surface antigens Plasmodium falciparum has evolved to avoid protective immune responses; as a result in endemic areas anti-malaria immunity develops gradually over many years of multiple and repeated infections. We are studying the role of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) expressed by asexual stages of P. falciparum responsible for the pathogenicity of severe malaria. The immunopathology of falciparum malaria has been linked to cyto-adhesion of infected erythrocytes to specific host receptors. A greater appreciation of the PfEMP1 molecules important for the development of protective immunity and immunopathology is a prerequisite for the rational discovery and development of a safe and protective anti-disease malaria vaccine. Here we review the role of ICAM-1 and EPCR receptor adhering falciparum-parasites in the development of severe malaria; we discuss our current research to understand the factors involved in the pathogenesis of cerebral malaria and the feasibility of developing a vaccine targeted specifically to prevent this disease.

Retinopathy-Positive Cerebral Malaria Is Associated With Greater Inflammation, Blood-Brain Barrier Breakdown, and Neuronal Damage Than Retinopathy-Negative Cerebral Malaria

BACKGROUND

Our prior study findings suggest that Plasmodium falciparum is the cause of disease in both malaria retinopathy-positive (RP) and most retinopathy-negative (RN) cerebral malaria (CM), and that absence of retinopathy and decreased disease severity in RN CM may be due to shorter duration of illness, lower parasite biomass, and decreased var gene expression in RN compared to RP CM. In the present study, we assessed the pathophysiology of RP and RN CM.

METHODS

We compared markers of systemic and central nervous system inflammation, oxidative stress, neuronal injury, systemic endothelial activation, angiogenesis, and platelet activation in Ugandan children with RP (n = 167) or RN (n = 87) CM.

RESULTS

RP children had higher plasma C-reactive protein (P = .013), ferritin and erythropoietin (both P < .001) levels, an elevated cerebrospinal fluid (CSF):plasma albumin ratio (P < .001), and higher CSF tau protein levels (P = .049) than RN children. Levels of plasma and CSF proinflammatory and anti-inflammatory cytokines and oxidative stress markers did not differ between RP and RN children. RN children had higher plasma levels of endothelin 1 (P = .003), platelet-derived growth factor (P = .012), and platelet factor 4 (P = .034).

CONCLUSIONS

RP and RN CM may represent different phases of CM. RN CM may be driven by early vasospasm and platelet activation, whereas the more advanced RP CM is associated with greater inflammation, increased erythropoietic drive, blood-brain barrier breakdown, and neuronal injury, each of which may contribute to greater disease severity.

Cerebral malaria is associated with differential cytoadherence to brain endothelial cells

Sequestration of Plasmodium falciparum‐infected erythrocytes (IE) within the brain microvasculature is a hallmark of cerebral malaria (CM). Using a microchannel flow adhesion assay with TNF‐activated primary human microvascular endothelial cells, we demonstrate that IE isolated from Malawian paediatric CM cases showed increased binding to brain microvascular endothelial cells compared to IE from uncomplicated malaria (UM) cases. Further, UM isolates showed significantly greater adhesion to dermal than to brain microvascular endothelial cells. The major mediator of parasite adhesion is P. falciparum erythrocyte membrane protein 1, encoded by var genes. Higher levels of var gene transcripts predicted to bind host endothelial protein C receptor (EPCR) and ICAM‐1 were detected in CM isolates. These data provide further evidence for differential tissue binding in severe and uncomplicated malaria syndromes, and give additional support to the hypothesis that CM pathology is based on increased cytoadherence of IE in the brain microvasculature.

Comparison of CD8+ T Cell Accumulation in the Brain During Human and Murine Cerebral Malaria

CD8⁺ T cells have been shown to play a critical role in the pathogenesis of experimental cerebral malaria (ECM) in mice, but their role in development of human cerebral malaria (HCM) remains unclear. Thus, in this study we have provided the first direct contrast of the accumulation of CD8⁺ T cells in the brain during HCM and ECM. HCM cases were from children who died of Plasmodium falciparum cerebral malaria at Queen Elizabeth Central Hospital (Malawi) between 2003 and 2010. ECM was induced by infecting C57BL/6J mice with P. berghei ANKA. We demonstrate similarities in the intracerebral CD8⁺ T cell responses in ECM and HCM, in particular an apparent shared choroid plexus-meningeal route of CD8⁺ T cell accumulation in the brain. Nevertheless, we also reveal some potentially important differences in compartmentalization of CD8⁺ T cells within the cerebrovascular bed in HCM and ECM.

Binding Heterogeneity of Plasmodium falciparum to Engineered 3D Brain Microvessels Is Mediated by EPCR and ICAM-1

Cerebral malaria research has been hindered by the inaccessibility of the brain. Here, we have developed an engineered 3D human brain microvessel model that mimics the blood flow rates and architecture of small blood vessels to study how P. falciparum-infected human erythrocytes attach to brain endothelial cells. By studying parasite lines with different adhesive properties, we show that the malaria parasite binding rate is heterogeneous and strongly influenced by physiological differences in flow and whether the endothelium has been previously activated by TNF-α, a proinflammatory cytokine that is linked to malaria disease severity. We also show the importance of human EPCR and ICAM-1 in parasite binding. Our model sheds new light on how P. falciparum binds within brain microvessels and provides a powerful method for future investigations of recruitment of human brain pathogens to the blood vessel lining of the brain.

Cerebral malaria is a severe neurological complication associated with sequestration of Plasmodium falciparum-infected erythrocytes (IE) in the brain microvasculature, but the specific binding interactions remain under debate. Here, we have generated an engineered three-dimensional (3D) human brain endothelial microvessel model and studied P. falciparum binding under the large range of physiological flow velocities that occur in both health and disease. Perfusion assays on 3D microvessels reveal previously unappreciated phenotypic heterogeneity in parasite binding to tumor necrosis factor alpha (TNF-α)-activated brain endothelial cells. While clonal parasite lines expressing a group B P. falciparum erythrocyte membrane protein 1 (PfEMP1) present an increase in binding to activated 3D microvessels, P. falciparum-IE expressing DC8-PfEMP1 present a decrease in binding. The differential response to endothelium activation is mediated by surface expression changes of endothelial protein C receptor (EPCR) and intercellular adhesion molecule 1 (ICAM-1). These findings demonstrate heterogeneity in parasite binding and provide evidence for a parasite strategy to adapt to a changing microvascular environment during infection. The engineered 3D human brain microvessel model provides new mechanistic insight into parasite binding and opens opportunities for further studies on malaria pathogenesis and parasite-vessel interactions.

The Ins and Outs of Cerebral Malaria Pathogenesis: Immunopathology, Extracellular Vesicles, Immunometabolism, and Trained Immunity

Complications from malaria parasite infections still cost the lives of close to half a million people every year. The most severe is cerebral malaria (CM). Employing murine models of CM, autopsy results, in vitro experiments, neuroimaging and microscopic techniques, decades of research activity have investigated the development of CM immunopathology in the hope of identifying steps that could be therapeutically targeted. Yet important questions remain. This review summarizes recent findings, primarily mechanistic insights on the essential cellular and molecular players involved gained within the murine experimental cerebral malaria model. It also highlights recent developments in (a) cell-cell communication events mediated through extracellular vesicles (EVs), (b) mounting evidence for innate immune memory, leading to “trained“ increased or tolerised responses, and (c) modulation of immune cell function through metabolism, that could shed light on why some patients develop this life-threatening condition whilst many do not.

What causes severe malaria and its complications in children? Lessons learned over the past 15 years

Over the past 15 years, malaria mortality has reduced by approximately 50%. However, malaria still causes more than 400,000 deaths annually, most of which occur in African children under 5 years of age. Significant advances in understanding the pathogenesis of the disease provide a basis for future work to prevent severe malaria and its complications. Herein, we provide an overview of advances in our understanding of severe malaria in African children over the past 15 years, highlighting key complications and identifying priorities to further reduce malaria-associated mortality.

A retinal model of cerebral malaria

Malaria is a causative factor in about 500.000 deaths each year world-wide. Cerebral malaria is a particularly severe complication of this disease and thus associated with an exceedingly high mortality. Malaria retinopathy is an ocular manifestation often associated with cerebral malaria, and presumably shares a substantial part of its pathophysiology. Here, we describe that indeed murine malaria retinopathy reproduced the main hallmarks of the corresponding human disease. In the living animal, we were able to follow the circulation and cellular localization of malaria parasites transgenically labelled with GFP via non-invasive in vivo retinal imaging. We found that malaria parasites cross the blood-retinal-barrier and infiltrate the neuroretina, concomitant with an extensive, irreversible, and long-lasting retinal neurodegeneration. Furthermore, anti-malarial treatment with dihydroartemisinin strongly diminished the load of circulating parasites but resolved the symptoms of the retinopathy only in part. In summary, we introduce here a novel preclinical model for human cerebral malaria that is much more directly accessible for studies into disease pathophysiology and development of novel treatment approaches. In vivo retinal imaging may furthermore serve as a valuable tool for the early diagnosis of the human disease.

Ocular Parasitosis Caused by Protozoan Infection during Travel: Focus on Prevention and Treatment

International travel is rising quickly worldwide. Many people travel to tropical and subtropical areas, where there has been increasing exposure of travelers to infectious pathogens. Ocular parasitic infections are more prevalent in these geographical areas and they can lead to morbidity and mortality, often due to late or misdiagnosis due to the unfamiliarity of health staff with these diseases. This is an up-to-date comprehensive review article that familiarizes physicians with ocular signs and symptoms, treatment, prevention, and geographic distribution of some parasites associated with travel.

Retinal Parameters as Compared with Head Circumference, Height, Weight, and Body Mass Index in Children in Kenya and Bhutan

The retina shares embryological derivation with the brain and may provide a new measurement of overall growth status, especially useful in resource-limited settings. Optical coherence tomography (OCT) provides detailed quantification of retinal structures. We enrolled community-dwelling children ages 3–11 years old in Siaya, Kenya and Thimphu, Bhutan in 2016. We measured head circumference (age < 5 years only), height, and weight, and standardized these by age and gender. Research staff performed OCT (iScan; Optovue, Inc., Fremont, CA), measuring the peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell complex (GCC) thicknesses. A neuro-ophthalmologist performed quality control for centration, motion artifact, and algorithm-derived quality scores. Generalized estimating equations were used to determine the relationship between anthropometric and retinal measurements. Two hundred and fifty-eight children (139 females, average age 6.4 years) successfully completed at least one retinal scan, totaling 1,048 scans. Nine hundred and twenty-two scans (88.0%) were deemed usable. Fifty-three of the 258 children (20.5%) were able to complete all six scans. Kenyan children had a thinner average GCC (P < 0.001) than Bhutanese children after adjustment for age and gender, but not RNFL (P = 0.70). In models adjusting for age, gender, and study location, none of standardized height, weight, and body mass index (BMI) were statistically significantly associated with RNFL or GCC. We determined that OCT is feasible in some children in resource-limited settings, particularly those > 4 years old, using the iScan device. We found no evidence for GCC or RNFL as a proxy for height-, weight-, or BMI-for-age. The variation in mean GCC thickness in Asian versus African children warrants further investigation.

Type I Interferon Receptor Variants in Gene Regulatory Regions are Associated with Susceptibility to Cerebral Malaria in Malawi

Cerebral malaria (CM) remains an important cause of morbidity and mortality. Risk for developing CM partially depends on host genetic factors, including variants encoded in the type I interferon (IFN) receptor 1 (IFNAR1). Type I IFNs bind to IFNAR1 resulting in increased expression of IFN responsive genes, which modulate innate and adaptive immune responses. To comprehensively study IFNAR1 genetic variant associations in Malawians with CM or uncomplicated malaria, we used a tag single nucleotide polymorphism approach, based on the HapMap Yoruba in Ibadan, Nigeria, population database. We identified three novel (rs914142, rs12626750, and rs1041867) and one previously published (Chr21:34696785 [C > G]) IFNAR1 variants to be associated with CM. Some of these variants are in gene regulatory regions. Chr21:34696785 (C > G) is in a region encoding histone modifications and transcription factor-binding sites, which suggests gene regulatory activity. Rs12626750 is predicted to bind embryonic lethal abnormal vision system-like RNA-binding protein 1, a RNA-binding protein which can increase the type I IFN response. Furthermore, we examined these variants in an expression quantitative trait loci database and found that a protective variant, rs914142, is associated with lower expression of IFNAR1, whereas the CM-associated variant rs12626750 was associated with increased IFNAR1 expression, suggesting that activation of the type I IFN pathway may contribute to pathogenesis of CM. Future functional studies of IFNAR1 variants are now needed to clarify the role of this pathway in severe malarial diseases.

Neurovascular sequestration in paediatric P. falciparum malaria is visible clinically in the retina

Retinal vessel changes and retinal whitening, distinctive features of malarial retinopathy, can be directly observed during routine eye examination in children with P. falciparum cerebral malaria. We investigated their clinical significance and underlying mechanisms through linked clinical, clinicopathological and image analysis studies. Orange vessels and severe foveal whitening (clinical examination, n = 817, OR, 95% CI: 2.90, 1.96-4.30; 3.4, 1.8-6.3, both p<0.001), and arteriolar involvement by intravascular filling defects (angiographic image analysis, n = 260, 2.81, 1.17-6.72, p<0.02) were strongly associated with death. Orange vessels had dense sequestration of late stage parasitised red cells (histopathology, n = 29; sensitivity 0.97, specificity 0.89) involving 360° of the lumen circumference, with altered protein expression in blood-retinal barrier cells and marked loss/disruption of pericytes. Retinal whitening was topographically associated with tissue response to hypoxia. Severe neurovascular sequestration is visible at the bedside, and is a marker of severe disease useful for diagnosis and management.

Tissue-specific immunopathology during malaria infection

Systemic inflammation mediated by Plasmodium parasites is central to malaria disease and its complications. Plasmodium parasites reside in erythrocytes and can theoretically reach all host tissues via the circulation. However, actual interactions between parasitized erythrocytes and host tissues, along with the consequent damage and pathological changes, are limited locally to specific tissue sites. Such tissue specificity of the parasite can alter the outcome of malaria disease, determining whether acute or chronic complications occur. Here, we give an overview of the recent progress that has been made in understanding tissue-specific immunopathology during Plasmodium infection. As knowledge on tissue-specific host-parasite interactions accumulates, better treatment modalities and targets may emerge for intervention in malaria disease.

Do we know enough to find an adjunctive therapy for cerebral malaria in African children?

Cerebral malaria is the deadliest complication of malaria, a febrile infectious disease caused by Plasmodium parasite. Any of the five human Plasmodium species can cause disease, but, for unknown reasons, in approximately 2 million cases each year P. falciparum progresses to severe disease, ultimately resulting in half a million deaths. The majority of these deaths are in children under the age of five. Currently, there is no way to predict which child will progress to severe disease and there are no adjunctive therapies to halt the symptoms after onset. Herein, we discuss what is known about the disease mechanism of one form of severe malaria, cerebral malaria, and how we might exploit this understanding to rescue children in the throes of cerebral disease.

Young Sprague Dawley rats infected by Plasmodium berghei: A relevant experimental model to study cerebral malaria

Cerebral malaria (CM) is the most severe manifestation of human malaria yet is still poorly understood. Mouse models have been developed to address the subject. However, their relevance to mimic human pathogenesis is largely debated. Here we study an alternative cerebral malaria model with an experimental Plasmodium berghei Keyberg 173 (K173) infection in Sprague Dawley rats. As in Human, not all infected subjects showed cerebral malaria, with 45% of the rats exhibiting Experimental Cerebral Malaria (ECM) symptoms while the majority (55%) of the remaining rats developed severe anemia and hyperparasitemia (NoECM). These results allow, within the same population, a comparison of the noxious effects of the infection between ECM and severe malaria without ECM. Among the ECM rats, 77.8% died between day 5 and day 12 post-infection, while the remaining rats were spontaneously cured of neurological signs within 24-48 hours. The clinical ECM signs observed were paresis quickly evolving to limb paralysis, global paralysis associated with respiratory distress, and coma. The red blood cell (RBC) count remained normal but a drastic decrease of platelet count and an increase of white blood cell numbers were noted. ECM rats also showed a decrease of glucose and total CO2 levels and an increase of creatinine levels compared to control rats or rats with no ECM. Assessment of the blood-brain barrier revealed loss of integrity, and interestingly histopathological analysis highlighted cyto-adherence and sequestration of infected RBCs in brain vessels from ECM rats only. Overall, this ECM rat model showed numerous clinical and histopathological features similar to Human CM and appears to be a promising model to achieve further understanding the CM pathophysiology in Humans and to evaluate the activity of specific antimalarial drugs in avoiding/limiting cerebral damages from malaria.

Evidence from a natural experiment that malaria parasitemia is pathogenic in retinopathy-negative cerebral malaria

Cerebral malaria (CM) can be classified as retinopathy-positive or retinopathy-negative, based on the presence or absence of characteristic retinal features. While malaria parasites are considered central to the pathogenesis of retinopathy-positive CM, their contribution to retinopathy-negative CM is largely unknown. One theory is that malaria parasites are innocent bystanders in retinopathy-negative CM and the etiology of the coma is entirely non-malarial. Because hospitals in malaria-endemic areas often lack diagnostic facilities to identify non-malarial causes of coma, it has not been possible to evaluate the contribution of malaria infection to retinopathy-negative CM. To overcome this barrier, we studied a natural experiment involving genetically inherited traits, and find evidence that malaria parasitemia does contribute to the pathogenesis of retinopathy-negative CM. A lower bound for the fraction of retinopathy-negative CM that would be prevented if malaria parasitemia were to be eliminated is estimated to be 0.93 (95% confidence interval: 0.68, 1).

Binding of Plasmodium falciparum to CD36 can be shielded by the glycocalyx

BACKGROUND

Plasmodium falciparum-infected erythrocytes sequester in the microcirculation due to interaction between surface-expressed parasite proteins and endothelial receptors. Endothelial cells are covered in a carbohydrate-rich glycocalyx that shields against undesired leukocyte adhesion. It was investigated if the cellular glycocalyx affects the binding of P. falciparum-infected erythrocytes to CD36 in vitro.

METHODS

Glycocalyx growth was followed in vitro by using azido sugars and cationized ferritin detecting O-glycoproteins and negatively charged proteoglycans, respectively. P. falciparum (clone FCR3/IT) was selected on Chinese hamster ovary (CHO) cells transfected with human CD36. Cytoadhesion to CHO CD36 at 1-4 days after seeding was quantified by using a static binding assay.

RESULTS

The glycocalyx thickness of CHO cells increased during 4 days in culture as assessed by metabolic labelling of glycans with azido sugars and with electron microscopy studying the binding of cationized ferritin to cell surfaces. The functional importance of this process was addressed in binding assays by using CHO cells transfected with CD36. In parallel with the maturation of the glycocalyx, antibody-binding to CD36 was inhibited, despite stable expression of CD36. P. falciparum selected for CD36-binding recognized CD36 on CHO cells on the first day in culture, but the binding was lost after 2-4 days.

CONCLUSION

The endothelial glycocalyx affects parasite cytoadhesion in vitro, an effect that has previously been ignored. The previously reported loss of glycocalyx during experimental malaria may play an important role in the pathogenesis of malaria complications by allowing the close interaction between infected erythrocytes and endothelial receptors.

Autophagy is required for cell survival under L-asparaginase-induced metabolic stress in acute lymphoblastic leukemia cells

L-asparaginase has been used for more than three decades in acute lymphoblastic leukemia (ALL) patients and remains an essential drug in the treatment of ALL. Poor response to L-asparaginase is associated with increased risk of therapeutic failure in ALL. However, both the metabolic perturbation and molecular context of L-asparaginase-treated ALL cells has not been fully elucidated. Here we identify that treatment with L-asparaginase results in metabolic shutdown via the reduction of both glycolysis and oxidative phosphorylation, accompanied by mitochondrial damage and activation of autophagy. The autophagy is involved in reducing reactive oxygen species (ROS) level by eliminating injured mitochondria. Inhibition of autophagy enhances L-asparaginase-induced cytotoxicity and overcomes the acquired resistance to L-asparaginase in ALL cells. The ROS-p53-positive feedback loop is an essential mechanism of this synergistic cytotoxicity. Thus, our findings provide the rationale for the future development of combined treatment of L-asparaginase and anti-autophagy drug in ALL patients.

The Severity of Plasmodium falciparum Infection Is Associated with Transcript Levels of var Genes Encoding Endothelial Protein C Receptor-Binding P. falciparum Erythrocyte Membrane Protein 1

By attaching infected erythrocytes to the vascular lining, Plasmodium falciparum parasites leave blood circulation and avoid splenic clearance. This sequestration is central to pathogenesis. Severe malaria is associated with parasites expressing an antigenically distinct P. falciparum erythrocyte membrane protein 1 (PfEMP1) subset mediating binding to endothelial receptors. Previous studies indicate that PfEMP1 adhesins with so-called CIDRα1 domains capable of binding endothelial protein C receptor (EPCR) constitute the PfEMP1 subset associated with severe pediatric malaria. To analyze the relative importance of different subtypes of CIDRα1 domains, we compared Pfemp1 transcript levels in children with severe malaria (including 9 fatal and 114 surviving cases), children hospitalized with uncomplicated malaria (n = 42), children with mild malaria not requiring hospitalization (n = 10), and children with parasitemia and no ongoing fever (n = 12). High levels of transcripts encoding EPCR-binding PfEMP1 were found in patients with symptomatic infections, and the abundance of these transcripts increased with disease severity. The compositions of CIDRα1 subtype transcripts varied markedly between patients, and none of the subtypes were dominant. Transcript-level analyses targeting other domain types indicated that subtypes of DBLβ or DBLζ domains might mediate binding phenomena that, in conjunction with EPCR binding, could contribute to pathogenesis. These observations strengthen the rationale for targeting the PfEMP1-EPCR interaction by vaccines and adjunctive therapies. Interventions should target EPCR binding of all CIDRα1 subtypes.

Automated Detection of Malarial Retinopathy in Digital Fundus Images for Improved Diagnosis in Malawian Children with Clinically Defined Cerebral Malaria

Cerebral malaria (CM), a complication of malaria infection, is the cause of the majority of malaria-associated deaths in African children. The standard clinical case definition for CM misclassifies ~25% of patients, but when malarial retinopathy (MR) is added to the clinical case definition, the specificity improves from 61% to 95%. Ocular fundoscopy requires expensive equipment and technical expertise not often available in malaria endemic settings, so we developed an automated software system to analyze retinal color images for MR lesions: retinal whitening, vessel discoloration, and white-centered hemorrhages. The individual lesion detection algorithms were combined using a partial least square classifier to determine the presence or absence of MR. We used a retrospective retinal image dataset of 86 pediatric patients with clinically defined CM (70 with MR and 16 without) to evaluate the algorithm performance. Our goal was to reduce the false positive rate of CM diagnosis, and so the algorithms were tuned at high specificity. This yielded sensitivity/specificity of 95%/100% for the detection of MR overall, and 65%/94% for retinal whitening, 62%/100% for vessel discoloration, and 73%/96% for hemorrhages. This automated system for detecting MR using retinal color images has the potential to improve the accuracy of CM diagnosis.

Clinical Comparison of Retinopathy-Positive and Retinopathy-Negative Cerebral Malaria

AbstractCerebral malaria (CM) is a severe and often lethal complication of falciparum malaria. A classic malaria retinopathy is seen in some (retinopathy-positive [RP]) children but not others (retinopathy-negative [RN]), and is associated with increased parasite sequestration. It is unclear whether RN CM is a severe nonmalarial illness with incidental parasitemia or a less severe form of the same malarial illness as RP CM. Understanding the clinical differences between RP and RN CM may help shed light on the pathophysiology of malarial retinopathy. We compared clinical history, physical examination, laboratory findings, and outcomes of RP (N = 167) and RN (N = 87) children admitted to Mulago Hospital, Kampala, Uganda. Compared with RN children, RP children presented with a longer history of illness, as well as physical examination and laboratory findings indicative of more severe disease and organ damage. The hospital course of RP children was complicated by longer coma duration and a greater transfusion burden than RN children. Mortality did not differ significantly between RP and RN children (14.4% versus 8.0%, P = 0.14). Further, severity of retinal hemorrhage correlated with the majority of variables that differed between RP and RN children. The data suggest that RP and RN CM may reflect the spectrum of illness in CM, and that RN CM could be an earlier, less severe form of disease.

EPCR and Malaria Severity: The Center of a Perfect Storm

Severe malaria due to Plasmodium falciparum infection causes nearly half a million deaths per year. The different symptomatology and disease manifestations among patients have hampered understanding of severe malaria pathology and complicated efforts to develop targeted disease interventions. Infected erythrocyte sequestration in the microvasculature plays a critical role in the development of severe disease, and there is increasing evidence that cytoadherent parasites interact with host factors to enhance the damage caused by the parasite. The recent discovery that parasite binding to endothelial protein C receptor (EPCR) is associated with severe disease has suggested new mechanisms of pathology and provided new avenues for severe malaria adjunctive therapy research.

Severe malaria: what's new on the pathogenesis front?

Plasmodium falciparum causes the most severe and fatal form of malaria in humans with over half a million deaths each year. Cerebral malaria, a complex neurological syndrome of severe falciparum malaria, is often fatal and represents a major public health burden. Despite vigorous efforts, the pathophysiology of cerebral malaria remains to be elucidated, thereby hindering the development of adjunctive therapies. In recent years, multidisciplinary and collaborative approaches have led to groundbreaking progress both in the laboratory and in the field. Here we review the latest breakthroughs in severe malaria pathogenesis, with a specific focus on new pathogenetic mechanisms leading to cerebral malaria. The most recent findings point towards specific parasite phenotypes targeting brain microvasculature, endothelial dysfunction and subsequent oedema-induced brain swelling.

Differential Plasmodium falciparum surface antigen expression among children with Malarial Retinopathy

Retinopathy provides a window into the underlying pathology of life-threatening malarial coma ("cerebral malaria"), allowing differentiation between 1) coma caused by sequestration of Plasmodium falciparum-infected erythrocytes in the brain and 2) coma with other underlying causes. Parasite sequestration in the brain is mediated by PfEMP1; a diverse parasite antigen that is inserted into the surface of infected erythrocytes and adheres to various host receptors. PfEMP1 sub-groups called "DC8" and "DC13" have been proposed to cause brain pathology through interactions with endothelial protein C receptor. To test this we profiled PfEMP1 gene expression in parasites from children with clinically defined cerebral malaria, who either had or did not have accompanying retinopathy. We found no evidence for an elevation of DC8 or DC13 PfEMP1 expression in children with retinopathy. However, the proportional expression of a broad subgroup of PfEMP1 called "group A" was elevated in retinopathy patients suggesting that these variants may play a role in the pathology of cerebral malaria. Interventions targeting group A PfEMP1 may be effective at reducing brain pathology.

The evidence for a role of vasospasm in the pathogenesis of cerebral malaria

Due to delay in treatment, cerebral malaria (CM) remains a significant complication of Plasmodium falciparum infection and is a common cause of death from malaria. In addition, more than 10 % of children surviving CM have neurological and long-term cognitive deficits. Understanding the pathogenesis of CM enables design of supportive treatment, reducing neurological morbidity and mortality. Vaso-occlusion and brain swelling appear to be leading to clinical features, neuronal damage and death in CM. It is proposed that parasitized red blood cells (pRBC), due to cytoadhesion to the endothelium and vasospasm induced by reduced bioavailability of nitric oxide, are causes. Stasis of blood flow and accumulation of pRBC may allow, after schizont rupture, for high concentration of products of haemolysis to accumulate, which leads to localized nitric oxide depletion, inducing adhesion molecules and cerebral vasospasm. Features consistent with an involvement of vasospasm are rapid reversibility of neurological symptoms, intermittently increased or absent flow in medium cerebral artery detectable on Doppler ultrasound and hemispheric reversible changes on cerebral magnetic resonance imaging in some patients. Clinical trials of treatment that can rapidly reduce cerebral vasospasm, including nitric oxide donors, inhaled nitric oxide, endothelin or calcium antagonists, or tissue plasminogen activators, are warranted.

Grading fluorescein angiograms in malarial retinopathy

BACKGROUND

Malarial retinopathy is an important finding in Plasmodium falciparum cerebral malaria, since it strengthens diagnostic accuracy, predicts clinical outcome and appears to parallel cerebral disease processes. Several angiographic features of malarial retinopathy have been described, but observations in different populations can only be reliably compared if consistent methodology is used to capture and grade retinal images. Currently no grading scheme exists for fluorescein angiographic features of malarial retinopathy.

METHODS

A grading scheme for fluorescein angiographic images was devised based on consensus opinion of clinicians and researchers experienced in malarial retinopathy in children and adults. Dual grading were performed with adjudication of admission fluorescein images from a large cohort of children with cerebral malaria.

RESULTS

A grading scheme is described and standard images are provided to facilitate future grading studies. Inter-grader agreement was >70 % for most variables. Intravascular filling defects are difficult to grade and tended to have lower inter-grader agreement (>57 %) compared to other features.

CONCLUSIONS

This grading scheme provides a consistent way to describe retinal vascular damage in paediatric cerebral malaria, and can facilitate comparisons of angiographic features of malarial retinopathy between different patient groups, and analysis against clinical outcomes. Inter-grader agreement is reasonable for the majority of angiographic signs. Dual grading with expert adjudication should be used to maximize accuracy.

Automated Detection of Vessel Abnormalities on Fluorescein Angiogram in Malarial Retinopathy

The detection and assessment of intravascular filling defects is important, because they may represent a process central to cerebral malaria pathogenesis: neurovascular sequestration. We have developed and validated a framework that can automatically detect intravascular filling defects in fluorescein angiogram images. It first employs a state-of-the-art segmentation approach to extract the vessels from images and then divide them into individual segments by geometrical analysis. A feature vector based on the intensity and shape of saliency maps is generated to represent the level of abnormality of each vessel segment. An AdaBoost classifier with weighted cost coefficient is trained to classify the vessel segments into normal and abnormal categories. To demonstrate its effectiveness, we apply this framework to 6,358 vessel segments in images from 10 patients with malarial retinopathy. The test sensitivity, specificity, accuracy, and area under curve (AUC) are 74.7%, 73.5%, 74.1% and 74.2% respectively when compared to the reference standard of human expert manual annotations. This performance is comparable to the agreement that we find between human observers of intravascular filling defects. Our method will be a powerful new tool for studying malarial retinopathy.

Correlation of hemorrhage, axonal damage, and blood-tissue barrier disruption in brain and retina of Malawian children with fatal cerebral malaria

Background: The retinal and brain histopathological findings in children who died from cerebral malaria (CM) have been recently described. Similar changes occur in both structures, but the findings have not been directly compared in the same patients. In this study, we compared clinical retinal findings and retinal and cerebral histopathological changes in a series of patients in Blantyre, Malawi, who died of CM.

Methods: The features systematically compared in the same patient were: (1) clinical, gross and microscopic retinal hemorrhages with microscopic cerebral hemorrhages, (2) retinal and cerebral hemorrhage-associated and -unassociated axonal damage, and fibrinogen leakage, and (3) differences in the above features between the pathological categories of CM without microvascular pathology (CM1) and CM with microvascular pathology (CM2) in retina and brain.

Results: Forty-seven patients were included: seven CM1, 28 CM2, and 12 controls. In the 35 malaria cases retinal and cerebral pathology correlated in all features except for non-hemorrhage associated fibrinogen leakage. Regarding CM1 and CM2 cases, the only differences were in the proportion of patients with hemorrhage-associated cerebral pathology, and this was expected, based on the definitions of CM1 and CM2. The retina did not show this difference. Non-hemorrhage associated pathology was similar for the two groups.

Comment: As postulated, histopathological features of hemorrhages, axonal damage and non-hemorrhage associated fibrinogen leakage correlated in the retina and brain of individual patients, although the difference in hemorrhages between the CM1 and CM2 groups was not consistently observed in the retina. These results help to underpin the utility of ophthalmoscopic examination and fundus findings to help in diagnosis and assessment of cerebral malaria patients, but may not help in distinguishing between CM1 and CM2 patients during life.

Developing retinal biomarkers of neurological disease: an analytical perspective

The inaccessibility of the brain poses a problem for neuroscience. Scientists have traditionally responded by developing biomarkers for brain physiology and disease. The retina is an attractive source of biomarkers since it shares many features with the brain. Some even describe the retina as a 'window' to the brain, implying that retinal signs are analogous to brain disease features. However, new analytical methods are needed to show whether or not retinal signs really are equivalent to brain abnormalities, since this requires greater evidence than direct associations between retina and brain. We, therefore propose a new way to think about, and test, how clearly one might see the brain through the retinal window, using cerebral malaria as a case study.