Blood Platelets as an Important but Underrated Circulating Source of TGFβ

When treating diseases related primarily to tissue remodeling and fibrosis, it is desirable to regulate TGFβ concentration and modulate its biological effects. The highest cellular concentrations of TGFβ are found in platelets, with about 40% of all TGFβ found in peripheral blood plasma being secreted by them. Therefore, an understanding of the mechanisms of TGFβ secretion from platelets may be of key importance for medicine. Unfortunately, despite the finding that platelets are an important regulator of TGFβ levels, little research has been carried out into the development of platelet-directed therapies that might modulate the TGFβ-dependent processes. Nevertheless, there are some very encouraging reports suggesting that platelet TGFβ may be specifically involved in cardiovascular diseases, liver fibrosis, tumour metastasis, cerebral malaria and in the regulation of inflammatory cell functions. The purpose of this review is to briefly summarize these few, extremely encouraging reports to indicate the state of current knowledge in this topic. It also attempts to better characterize the influence of TGFβ on platelet activation and reactivity, and its shaping of the roles of blood platelets in haemostasis and thrombosis.

Diffusion-Weighted MR Imaging in a Prospective Cohort of Children with Cerebral Malaria Offers Insights into Pathophysiology and Prognosis

BACKGROUND AND PURPOSE

Validation of diffusion-weighted images obtained on 0.35T MR imaging in Malawi has facilitated meaningful review of previously unreported findings in cerebral malaria. Malawian children with acute cerebral malaria demonstrated restricted diffusion on brain MR imaging, including an unusual pattern of restriction isolated to the subcortical white matter. We describe the patterns of diffusion restriction in cerebral malaria and further evaluate risk factors for and outcomes associated with an isolated subcortical white matter diffusion restriction.

MATERIALS AND METHODS

Between 2009 and 2014, comatose Malawian children admitted to the hospital with cerebral malaria underwent admission brain MR imaging. Imaging data were compiled via NeuroInterp, a RedCap data base. Clinical information obtained included coma score, serum studies, and coma duration. Electroencephalograms were obtained between 2009 and 2011. Outcomes captured included death, neurologic sequelae, or full recovery.

RESULTS

One hundred ninety-four/269 (72.1%) children with cerebral malaria demonstrated at least 1 area of diffusion restriction. The most common pattern was bilateral subcortical white matter involvement (41.6%), followed by corpus callosum (37.5%), deep gray matter (36.8%), cortical gray matter (17.8%), and posterior fossa (8.9%) involvement. Sixty-one (22.7%) demonstrated isolated subcortical white matter diffusion restriction. These children had lower whole-blood lactate levels (OR, 0.9; 95% CI, 0.85-0.98), were less likely to require anticonvulsants (OR, 0.6; 95% CI, 0.30-0.98), had higher average electroencephalogram voltage (OR, 1.01; 95% CI, 1.00-1.02), were less likely to die (OR, 0.09; 95% CI, 0.01-0.67), and were more likely to recover without neurologic sequelae (OR, 3.7; 95% CI, 1.5-9.1).

CONCLUSIONS

Restricted diffusion is common in pediatric cerebral malaria. Isolated subcortical white matter diffusion restriction is a unique imaging pattern associated with less severe disease and a good prognosis for full recovery. The underlying pathophysiology may be related to selective white matter vulnerability.

Experimental Cerebral Malaria Alters Blood Lipid Levels During Pathogenesis

Malaria infection threatens millions of people worldwide. Sequestering of Plasmodium-infected erythrocytes within the blood vessels of the brain may lead to a more severe form of disease called cerebral malaria (CM), which is difficult to diagnose and treat. Here we used C57BL/6 mice to establish a model of experimental CM (ECM). Comparing the dosage dependence of ECM induction, we found that inoculation with 1×10³ parasitized erythrocytes had higher efficiency at establishing ECM than 1×10⁶ parasitized erythrocytes. However, the percentage of ECM varied in different experimental batches. Infected mice that developed ECM had elevated serum levels of total cholesterol and decreased serum levels of high-density lipoprotein and low-density lipoprotein cholesterol. In addition, ECM mice exhibited liver and kidney dysfunction. ECM induced by low dose inoculation requires additional verification for efficiency. Biochemical analysis of ECM mice revealed characteristic blood lipid levels. These findings provide new clues for the diagnosis and mechanistic probing of CM pathogenesis.

In vivo noninvasive visualization of retinal perfusion dysfunction in murine cerebral malaria by camera-phone laser speckle imaging

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection associated with impaired cerebral blood flow. Visualization of the eye vasculature, which is embryologically derived from that of the brain, is used clinically to diagnose the syndrome. Here, we introduce camera-phone laser speckle imaging as a new tool for in vivo, noncontact two-dimensional mapping of blood flow dynamics in the experimental cerebral malaria (ECM) murine model of Plasmodium berghei ANKA. In a longitudinal study, we show that the camera-phone imager can detect an overall decrease in the retinal blood-flow-speed (BFS) as ECM develops in P. berghei ANKA infected mice, with no similar change observed in uninfected control mice or mice infected with a non-ECM inducing strain (P. berghei NK65). Furthermore, by analyzing relative alterations in the BFS of individual retinal vessels during the progression of ECM, we illustrate the strength of our imager in identifying different BFS-change heterogeneities in the retinas of ECM and uninfected mice. The technique creates new possibilities for objective investigations into the diagnosis and pathogenesis of CM noninvasively through the eye. The camera-phone laser speckle imager along with measured spatial blood perfusion maps of the retina of a mouse infected with P. berghei ANKA-a fatal ECM model-on different days during the progression of the infection (top, day 3 after infection; middle, day 5 after infection; and bottom, day 7 after infection).

Differential plasma microvesicle and brain profiles of microRNA in experimental cerebral malaria

BACKGROUND

Cerebral malaria (CM) is a fatal complication of Plasmodium infection, mostly affecting children under the age of five in the sub-Saharan African region. CM pathogenesis remains incompletely understood, although sequestered infected red blood cells, inflammatory cells aggregating in the cerebral blood vessels, and the microvesicles (MV) that they release in the circulation, have been implicated. Plasma MV numbers increase in CM patients and in the murine model, where blocking their release, genetically or pharmacologically, protects against brain pathology, suggesting a role of MV in CM neuropathogenesis. In this work, the microRNA (miRNA) cargo of MV is defined for the first time during experimental CM with the overarching hypothesis that this characterization could help understand CM pathogenesis.

RESULTS

The change in abundance of miRNA was studied following infection of CBA mice with Plasmodium berghei ANKA strain (causing experimental CM), and Plasmodium yoelii, which causes severe malaria without cerebral complications, termed non-CM (NCM). miRNA expression was analyzed using microarrays to compare MV from healthy (NI) and CM mice, yielding several miRNA of interest. The differential expression profiles of these selected miRNA (miR-146a, miR-150, miR-193b, miR-205, miR-215, miR-467a, and miR-486) were analyzed in mouse MV, MV-free plasma, and brain tissue by quantitative reverse transcription PCR (RT-qPCR). Two miRNA-miR-146a and miR-193b-were confirmed as differentially abundant in MV from CM mice, compared with NCM and NI mice. These miRNA have been shown to play various roles in inflammation, and their dysregulation during CM may be critical for triggering the neurological syndrome via regulation of their potential downstream targets.

CONCLUSIONS

These data suggest that, in the mouse model at least, miRNA may have a regulatory role in the pathogenesis of severe malaria.

Malarial hepatopathy: Clinical profile and association with other malarial complications

This prospective study assessed the incidence, clinical profile and outcome of malarial hepatopathy and its association with other complications in patients with malaria, proved by peripheral blood smear examination and rapid malaria test. Hyperbilirubinemia (Serum bilirubin >3mg/dL) with >3-fold rise in serum aminotransferases in absence of a different explanation for such derangement was considered as malarial hepatopathy. Of 134 (falciparum-81, vivax-48 and mixed falciparum and vivax-5) malaria cases, hyperbilirubinemia occurred in 41.04%. Serum aspartate aminotransferase (AST) was raised >3-fold in 17.16% and serum alanine aminotransferase (ALT) in 4.47% cases. Malarial hepatopathy was observed in 4.47% (falciparum-5 and vivax malaria-1) cases, but had insignificant association with the type of malaria (p=0.532). Serum bilirubin, AST and ALT levels were higher while age was lower in both overall (p<0.05 each) and falciparum malaria cases with hepatopathy than without hepatopathy (p<0.05 each). Malarial hepatopathy was associated with a higher incidence of cerebral malaria, shock, acute respiratory distress syndrome (ARDS) and acute kidney injury in both overall (p<0.05 each) and falciparum malaria (p<0.05 each) and hyponatremia and disseminated intravascular coagulation only in overall malaria (p<0.05). Malarial hepatopathy had significant association with duration of hospitalization, parasite clearance time, fever clearance time and jaundice clearance time in overall (p<0.05 each) and falciparum (p<0.05 each) but not vivax malaria cases (p>0.05 each). Mortality occurred in 1 (20%) case of falciparum-induced hepatopathy with an overall mortality of 16.66%. ARDS (p=0.003) and shock (p=0.026) were independently associated with malarial hepatopathy overall while only ARDS with falciparum-induced hepatopathy (p=0.006). Thus, hepatocellular dysfunction is common in malaria but that qualifying as malarial hepatopathy is not common. Malarial hepatopathy is likely to occur in presence of other malarial complications. It is an epiphenomenon in severe malaria and indicative of severe disease. Establishing a particular association with malaria or mortality would require a larger case-control study of severe malaria.

Real-time imaging reveals the dynamics of leukocyte behaviour during experimental cerebral malaria pathogenesis

During experimental cerebral malaria (ECM) mice develop a lethal neuropathological syndrome associated with microcirculatory dysfunction and intravascular leukocyte sequestration. The precise spatio-temporal context in which the intravascular immune response unfolds is incompletely understood. We developed a 2-photon intravital microscopy (2P-IVM)-based brain-imaging model to monitor the real-time behaviour of leukocytes directly within the brain vasculature during ECM. Ly6C^hi monocytes, but not neutrophils, started to accumulate in the blood vessels of Plasmodium berghei ANKA (PbA)-infected MacGreen mice, in which myeloid cells express GFP, one to two days prior to the onset of the neurological signs (NS). A decrease in the rolling speed of monocytes, a measure of endothelial cell activation, was associated with progressive worsening of clinical symptoms. Adoptive transfer experiments with defined immune cell subsets in recombinase activating gene (RAG)-1-deficient mice showed that these changes were mediated by Plasmodium-specific CD8⁺ T lymphocytes. A critical number of CD8⁺ T effectors was required to induce disease and monocyte adherence to the vasculature. Depletion of monocytes at the onset of disease symptoms resulted in decreased lymphocyte accumulation, suggesting reciprocal effects of monocytes and T cells on their recruitment within the brain. Together, our studies define the real-time kinetics of leukocyte behaviour in the central nervous system during ECM, and reveal a significant role for Plasmodium-specific CD8⁺ T lymphocytes in regulating vascular pathology in this disease.

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection that takes a significant toll on human life. Blockage of the brain blood vessels contributes to the clinical signs of CM, however we know little about the precise pathological events that lead to this disease. To this end, studies in Plasmodium-infected mice, that also develop a similar fatal disease, have proven useful. These studies have revealed an important role for leukocytes not so much in protecting but rather promoting pathology in the brain. To better understand leukocyte behaviour during experimental CM, we established a brain-imaging model that allows us to ‘peek’ into the brain of living mice and watch immunological events as they unfold. We found that worsening of disease was accompanied by an accumulation of monocytes in the blood vessels. Monocyte accumulation was regulated by activated CD8⁺ T cells but only when present in critical numbers. Monocyte depletion resulted in reduced T cell trafficking to the brain, but this did not result in improved disease outcome. Our studies reveal the orchestration of leukocyte accumulation in real time during CM, and demonstrate that CD8⁺ T cells play a crucial role in promoting clinical signs in this disease.

Factors associated with cerebral malaria

We conducted a retrospective unmatched case-control study using the medical records of patients admitted to the Hospital for Tropical Diseases, Mahidol University, Bangkok, Thailand to investigate factors associated with cerebral malaria. The records of 137 patients with severe Plasmodium falciparum without cerebral malaria and 35 patients with cerebral malaria hospitalized during 1997-2005 were reviewed and compared. Ten factors associated with cerebral malaria were identified: pulmonary edema [odds ratio (OR)= 13.8; 95% confidence interval (CI): 1.3-143.2], splenomegaly (OR=3.7; 95% CI: 1.3-44.7), fever (OR=3.3; 95% CI: 1.7-14.3), day 1 malarial density < or = 249,999/microl (OR=1.6; 95% CI: 1.1-14.6), day 2 malarial density < or =249,999/microl (OR=3.4; 95% CI: 1.3-35.1), dyspnea (OR=1.4; 95% CI: 1.2-12.1), hepatomegaly (OR=1.8; 95% CI: 0.2-12.1), being a referred patient (OR=1.3; 95% CI: 1.0-2.2), a higher systolic blood pressure (OR=1.2; 95% CI: 1.0-2.1) and a higher body mass index (OR=1.6; 95% CI: 1.0-2.6). Pulmonary edema was the strongest factor associated with cerebral malaria in our study. Clinicians who treat patients with severe Plasmodium falciparum malaria should be aware these factors are associated with cerebral malaria.

[Tropical malaria in children in the Republic of Tajikistan]

The complications of tropical malaria were noted in 25 (9.4%) of 196 pediatric patients followed up. These included cerebral malaria in 8 (3%), severe hemolytic anemia in 15 (5.7%), hemoglobinuric fever in 1 (0.37%), and malarial hepatitis in 1 (0.37%). The occurrence of complications was associated with the late referral of patients to a health care facility and untimely treatment, as well as with preliminary misdiagnoses (acute respiratory viral infection, typhoid-parathyphoid fever, meningitis, acute enteric infection, viral hepatitis, sepsis). The main reasons for late diagnosis were the absence of malarial paroxysm at the onset of disease in infants and the wrong type of a temperature curve.

Nitric oxide synthase dysfunction contributes to impaired cerebroarteriolar reactivity in experimental cerebral malaria

Cerebrovascular dysfunction plays a key role in the pathogenesis of cerebral malaria. In experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA, cerebrovascular dysfunction characterized by vascular constriction, occlusion and damage results in impaired perfusion and reduced cerebral blood flow and oxygenation, and has been linked to low nitric oxide (NO) bioavailability. Here, we directly assessed cerebrovascular function in ECM using a novel cranial window method for intravital microscopy of the pial microcirculation and probed the role of NOS isoforms and phosphorylation patterns in the impaired vascular responses. We show that pial arteriolar responses to endothelial NOS (eNOS) and neuronal NOS (nNOS) agonists (Acetylcholine (ACh) and N-Methyl-D-Aspartate (NMDA)) were blunted in mice with ECM, and could be partially recovered by exogenous supplementation of tetrahydrobiopterin (BH4). Pial arterioles in non-ECM mice infected by Plasmodium berghei NK65 remained relatively responsive to the agonists and were not significantly affected by BH4 treatment. These findings, together with the observed blunting of NO production upon stimulation by the agonists, decrease in total NOS activity, augmentation of lipid peroxidation levels, upregulation of eNOS protein expression, and increase in eNOS and nNOS monomerization in the brain during ECM development strongly indicate a state of eNOS/nNOS uncoupling likely mediated by oxidative stress. Furthermore, the downregulation of Serine 1176 (S1176) phosphorylation of eNOS, which correlated with a decrease in cerebrovascular wall shear stress, implicates hemorheological disturbances in eNOS dysfunction in ECM. Finally, pial arterioles responded to superfusion with the NO donor, S-Nitroso-L-glutathione (GSNO), but with decreased intensity, indicating that not only NO production but also signaling is perturbed during ECM. Therefore, the pathological impairment of eNOS and nNOS functions contribute importantly to cerebrovascular dysfunction in ECM and the recovery of intrinsic functionality of NOS to increase NO bioavailability and restore vascular health represents a target for ECM treatment.

Treatment of cerebral malaria and acute respiratory distress syndrome (ARDS) with parenteral artesunate

Infection with Plasmodium Falciparum can cause a severe form of malaria with multiorgan involvement. Cerebrum is one of the organs involved in the P. Falciparum malaria, which can lead to coma, convulsions, and other neurological sequel. The sequestration of cerebral vasculature with parasitized red blood cells is one of the proposed mechanisms for the development of cerebral malaria. We present a case of malaria with multi organ involvement. Cerebral malaria should be suspected in any febrile patient from a malaria-endemic region with loss of consciousness. Compared with quinine, intravenous artemisinin compounds (artesunate, arteether, artemether) are well tolerated by patients and have fewer side effects. Due to multi-organ involvement in P. Falciparum malaria, supportive therapy is crucial along with parenteral antimalarial to improve survival.

The association between cognition and academic performance in Ugandan children surviving malaria with neurological involvement

Background

The contribution of different cognitive abilities to academic performance in children surviving cerebral insult can guide the choice of interventions to improve cognitive and academic outcomes. This study's objective was to identify which cognitive abilities are associated with academic performance in children after malaria with neurological involvement.

Methods

62 Ugandan children with a history of malaria with neurological involvement were assessed for cognitive ability (working memory, reasoning, learning, visual spatial skills, attention) and academic performance (reading, spelling, arithmetic) three months after the illness. Linear regressions were fit for each academic score with the five cognitive outcomes entered as predictors. Adjusters in the analysis were age, sex, education, nutrition, and home environment. Exploratory factor analysis (EFA) and structural equation models (SEM) were used to determine the nature of the association between cognition and academic performance. Predictive residual sum of squares was used to determine which combination of cognitive scores was needed to predict academic performance.

Results

In regressions of a single academic score on all five cognitive outcomes and adjusters, only Working Memory was associated with Reading (coefficient estimate = 0.36, 95% confidence interval = 0.10 to 0.63, p<0.01) and Spelling (0.46, 0.13 to 0.78, p<0.01), Visual Spatial Skills was associated with Arithmetic (0.15, 0.03 to 0.26, p<0.05), and Learning was associated with Reading (0.06, 0.00 to 0.11, p<0.05). One latent cognitive factor was identified using EFA. The SEM found a strong association between this latent cognitive ability and each academic performance measure (P<0.0001). Working memory, visual spatial ability and learning were the best predictors of academic performance.

Conclusion

Academic performance is strongly associated with the latent variable labelled “cognitive ability” which captures most of the variation in the individual specific cognitive outcome measures. Working memory, visual spatial skills, and learning together stood out as the best combination to predict academic performance.

Delayed gastric emptying time in adult cerebral Falciparum malaria

OBJECTIVE

We hypothesize that upper gastrointestinal symptoms in cerebral malaria are due to gastric motor dysfunction. But gastric motility studies in cerebral malaria are scarce.

METHODS

We determined gastric emptying half-time (GET½) of liquid meals quantitatively by radio isotope scintigraphy in 25 patients of cerebral malaria and 10 healthy controls.

RESULTS

GET½ was prolonged (46.5 ± 4.8 min) significantly (p <0.001) in patients of cerebral malaria compared to healthy controls (27.6 ± 5.3 min).

CONCLUSION

Cerebral malaria can cause prolongation of gastric emptying time of liquid foods.

Altered regulation of Akt signaling with murine cerebral malaria, effects on long-term neuro-cognitive function, restoration with lithium treatment

Neurological and cognitive impairment persist in more than 20% of cerebral malaria (CM) patients long after successful anti-parasitic treatment. We recently reported that long term memory and motor coordination deficits are also present in our experimental cerebral malaria model (ECM). We also documented, in a murine model, a lack of obvious pathology or inflammation after parasite elimination, suggesting that the long-term negative neurological outcomes result from potentially reversible biochemical and physiological changes in brains of ECM mice, subsequent to acute ischemic and inflammatory processes. Here, we demonstrate for the first time that acute ECM results in significantly reduced activation of protein kinase B (PKB or Akt) leading to decreased Akt phosphorylation and inhibition of the glycogen kinase synthase (GSK3β) in the brains of mice infected with Plasmodium berghei ANKA (PbA) compared to uninfected controls and to mice infected with the non-neurotrophic P. berghei NK65 (PbN). Though Akt activation improved to control levels after chloroquine treatment in PbA-infected mice, the addition of lithium chloride, a compound which inhibits GSK3β activity and stimulates Akt activation, induced a modest, but significant activation of Akt in the brains of infected mice when compared to uninfected controls treated with chloroquine with and without lithium. In addition, lithium significantly reversed the long-term spatial and visual memory impairment as well as the motor coordination deficits which persisted after successful anti-parasitic treatment. GSK3β inhibition was significantly increased after chloroquine treatment, both in lithium and non-lithium treated PbA-infected mice. These data indicate that acute ECM is associated with abnormalities in cell survival pathways that result in neuronal damage. Regulation of Akt/GSK3β with lithium reduces neuronal degeneration and may have neuroprotective effects in ECM. Aberrant regulation of Akt/GSK3β signaling likely underlies long-term neurological sequelae observed in ECM and may yield adjunctive therapeutic targets for the management of CM.

Elevated cell-specific microparticles are a biological marker for cerebral dysfunctions in human severe malaria

Cerebral malaria (CM) and severe anemia (SA) are the most severe complications of Plasmodium falciparum infections. Although increased release of endothelial microparticles (MP) correlates with malaria severity, the full extent of vascular cell vesiculation remains unknown. Here, we characterize the pattern of cell-specific MP in patients with severe malaria. We tested the hypothesis that systemic vascular activation contributes to CM by examining origins and levels of plasma MP in relation to clinical syndromes, disease severity and outcome. Patients recruited in Douala, Cameroon, were assigned to clinical groups following WHO criteria. MP quantitation and phenotyping were carried out using cell-specific markers by flow cytometry using antibodies recognizing cell-specific surface markers. Platelet, erythrocytic, endothelial and leukocytic MP levels were elevated in patients with cerebral dysfunctions and returned to normal by discharge. In CM patients, platelet MP were the most abundant and their levels significantly correlated with coma depth and thrombocytopenia. This study shows for the first time a widespread enhancement of vesiculation in the vascular compartment appears to be a feature of CM but not of SA. Our data underpin the role of MP as a biomarker of neurological involvement in severe malaria. Therefore, intervention to block MP production in severe malaria may provide a new therapeutic pathway.

Murine malaria is associated with significant hearing impairment

BACKGROUND

Plasmodium falciparum malaria has been suspected to cause hearing loss. Developmental, cognitive and language disorders have been observed in children, surviving cerebral malaria. This prospective study aims to evaluate whether malaria influences hearing in mice.

METHODS

Twenty mice were included in a standardized murine cerebral malaria model. Auditory evoked brainstem responses were assessed before infection and at the peak of the illness.

RESULTS

A significant hearing impairment could be demonstrated in mice with malaria, especially the cerebral form. The control group did not show any alterations. No therapy was used.

CONCLUSION

This suggests that malaria itself leads to a hearing impairment in mice.

[Tropical causes of epilepsy]

INTRODUCTION

Eighty-five percent of all epileptics live in tropical regions. Prenatal risk factors, traumatic brain injuries and different parasitic infestations of the central nervous system (CNS) are the reasons behind the high prevalence of epilepsy. This work reviews the main parasitic infestations causing epilepsy in the tropics.

DEVELOPMENT

Neurocysticercosis is the main cause of focal epilepsy in early adulthood in endemic areas (30-50%). All the phases of cysticerci (viable, transitional and calcified) are associated with epileptic seizures. Anti-cysticercus treatment helps get rid of cysticerci faster and reduces the risk of recurrence of seizures in patients with viable cysts. Symptomatic epilepsy can be the first manifestation of neuroschistosomiasis in patients without any systemic symptoms. The pseudotumoral form can trigger seizures secondary to the presence of granulomas and oedemas in the cerebral cortex. The eggs of Schistosoma japonicum are smaller, reach the CNS more easily and trigger epileptic seizures more frequently. Toxocariasis and sparganosis are other parasitic infestations that can give rise to symptomatic seizures. The risk factors for suffering chronic epilepsy after cerebral malaria are a positive familial history of epilepsy and a history of episodes of fever and cerebral malaria that began with coma or which progressed with multiple, prolonged epileptic seizures. About 20% of patients with cerebral infarction secondary to Chagas disease present late vascular epilepsy as a complication.

CONCLUSIONS

Very few studies have been conducted to examine the prognosis, risk of recurrence and modification of the natural course of seizures associated with tropical parasitic infestations, except for the case of neurocysticercosis.

The eye in cerebral malaria: what can it teach us?

The pathophysiology of coma in cerebral malaria (CM) is not well understood. Obstruction of microcirculatory flow is thought to play a central role, but other hypotheses include roles for parasite- and host-derived factors such as immune mediators, and for increased blood-brain barrier permeability leading to raised intracranial pressure. The retinal vasculature is a direct extension of the cerebral vasculature. It is the only vascular bed easily accessible for visualisation and provides a unique opportunity to observe vascular pathology and its effect on neurological tissue. A specific retinopathy has been well described in African children with CM and its severity correlates with outcome. This retinopathy has been less well described in adults. The central mechanism causing malarial retinopathy appears to be microvascular obstruction, which has been demonstrated in affected retinas by fluorescein angiography. The presence in a central nervous system tissue of microvascular obstruction strongly supports the hypothesis that the sequestration of erythrocytes in small blood vessels and consequent obstruction of microcirculatory flow is an important mechanism causing coma and death in CM. Despite advances in the antimalarial treatment of severe malaria, its mortality remains approximately 15-20%. Adjunctive treatment targeting sequestration is a promising strategy to further lower mortality.

[Cerebral malaria]

Cerebral malaria (CM) is a life-threatening complication of falciparum malaria and some types of disturbed consciousness problems are major symptoms of CM. Although the pathogenesis of CM is unknown, the sequestration, the binding of red blood cells containing mature stages of the malaria parasite to the endothelium of the cerebral microvasculature, and the disappearance of erythrocytes infected with mature malaria parasite in the peripheral blood stream, are thought to play a key role in its pathogenesis. Falciparum malaria patients with disturbed consciousness should be considered to suffer from CM; however it should also be examined as to whether other disease complications such as meningitis or hypoglycemia are associated with this condition. The brain CT or MRI of CM patients reveal no specific findings. CM is treated with an intravenous infusion of artesunate or an intravenous drip infusion of quinine. The prognosis of CM patients is very poor without rapid and adequate treatment; therefore, CM is an infectious disease warranting emergency treatment. The number of Japanese CM patients is believed to increase in the near future in accordance with the increase in the number of Japanese travelers visiting tropical or subtropical malaria-endemic areas. Therefore, Japanese clinicians should also be aware of CM, in case a falciparum malaria patient with some consciousness disturbance visits the clinic.

Severe Plasmodium vivax malaria: a report on serial cases from Bikaner in northwestern India

Epidemiologic studies and clinical description of severe Plasmodium vivax malaria in adults living in malaria-endemic areas are rare and more attention is needed to understand the dynamics and its interaction with the immune system. This observational study included 1,091 adult patients admitted to medical wards of S. P. Medical College and associated group of hospitals in Bikaner, India from September 2003 through December 2005. The diagnosis of P. vivax malaria was established by peripheral blood film (PBF), rapid diagnostic test (RDT), and polymerase chain reaction (PCR), and severe malaria was categorized as per World Health Organization guidelines. Of 1,091 patients with malaria, 635 had P. falciparum malaria and 456 had P. vivax malaria. Among patients with severe manifestations, 40 had evidence of monoinfection of P. vivax malaria diagnosed by PBF, RDT, and PCR. Complications observed were hepatic dysfunction and jaundice in 23 (57.5%) patients, renal failure in 18 (45%) patients, severe anemia in 13 (32.5%) patients, cerebral malaria in 5 patients (12.5%), acute respiratory distress syndrome in 4 patients (10%), shock in 3 patients (7.5%), and hypoglycemia in 1 (2.5%) patient. Thrombocytopenia was observed in 5 (12.5%) patients, and multi-organ dysfunction was detected in 19 (47.5%) patients. Further large-scale multicentric epidemiologic studies are needed to define the basic pathology of this less known entity.

Challenges in the determination of early predictors of cerebral malaria: lessons from the human disease and the experimental murine models

Cerebral malaria (CM) is a life-threatening complication of malaria caused by Plasmodium falciparum, and it claims around two million lives a year, mainly those of children in sub-Saharan Africa. A number of works, particularly in murine models of CM, showed that several mediators are involved in the development of the disease, including monocytes, T lymphocytes, cytokines, chemokines, platelets, nitric oxide scavengers and heme, among others, but a comprehensive understanding of the pathogenesis of this complication is still lacking. This overview critically analyzes and discusses the definition, clinical features, neurocognitive outcomes and pathogenesis of human CM. We focused on the relationship between clinical and laboratory features and the diagnosis and prognosis of the complication showing indicators of poor prognosis and emphasizing the need of establishing predictive scores to estimate, on admission, the likelihood of any malarial patient to develop neurological complications. The potential development of a mathematical model for early prediction of CM through neurological assessment using the SHIRPA protocol in Plasmodium berghei ANKA-infected susceptible mice is shown. High positive predictive values (>89%) on days 5 and 6 of infection, observed for some generated SHIRPA scores, indicate the possibility of early detection of mice with a high probability of developing CM.

Cerebral malaria

Malaria infection of the Central Nervous System (CNS) can cause a severe neurological syndrome termed Cerebral Malaria (CM). The central neuropathological feature of CM is the preferential sequestration of parasitised red blood cells (PRBC) in the cerebral microvasculature. The level of sequestration is related to the incidence of cerebral symptoms in severe malaria. Other neuropathological features of CM include petechial hemorrhages in the brain parenchyma, ring hemorrhages and Dürck's granuloma's. Immunohisto-chemical and electron microscopy studies have shown widespread cerebral endothelial cell activation and morphological changes occur in CM, as well as focal endothelial cell damage and necrosis. The immune cell response to intravascular sequestration appears to be limited, although activation of pigment-phagocytosing monocytes is a late feature. The mechanisms by which PRBC cause coma in malaria remain unclear. In vitro parasitised erythrocytes bind to endothelial cells by specific, receptor mediated interactions with host adhesion molecules such as ICAM-1, whose expression on cerebral endothelial cells is increased during CM as part of a systemic endothelial activation. Induction of local neuro-active mediators such as nitric oxide and systemic cytokines like TNF alpha may be responsible for the rapidly reversible symptoms of the coma of CM. The recent cloning of the parasite ligand PfEMP-1, thought to mediate binding to host sequestration receptors, promises further insight into the relationship between patterns of sequestration and the incidence and pathogenesis of coma in cerebral malaria.

Burden, features, and outcome of neurological involvement in acute falciparum malaria in Kenyan children

CONTEXT

Plasmodium falciparum appears to have a particular propensity to involve the brain but the burden, risk factors, and full extent of neurological involvement have not been systematically described.

OBJECTIVES

To determine the incidence and describe the clinical phenotypes and outcomes of neurological involvement in African children with acute falciparum malaria.

DESIGN, SETTING, AND PATIENTS

A review of records of all children younger than 14 years admitted to a Kenyan district hospital with malaria from January 1992 through December 2004. Neurological involvement was defined as convulsive seizures, agitation, prostration, or impaired consciousness or coma.

MAIN OUTCOME MEASURES

The incidence, pattern, and outcome of neurological involvement.

RESULTS

Of 58,239 children admitted, 19,560 (33.6%) had malaria as the primary clinical diagnosis. Neurological involvement was observed in 9313 children (47.6%) and manifested as seizures (6563/17,517 [37.5%]), agitation (316/11,193 [2.8%]), prostration (3223/15,643 [20.6%]), and impaired consciousness or coma (2129/16,080 [13.2%]). In children younger than 5 years, the mean annual incidence of admissions with malaria was 2694 per 100,000 persons and the incidence of malaria with neurological involvement was 1156 per 100,000 persons. However, readmissions may have led to a 10% overestimate in incidence. Children with neurological involvement were older (median, 26 [interquartile range {IQR}, 15-41] vs 21 [IQR, 10-40] months; P<.001), had a shorter duration of illness (median, 2 [IQR, 1-3] vs 3 [IQR, 2-3] days; P<.001), and a higher geometric mean parasite density (42.0 [95% confidence interval {CI}, 40.0-44.1] vs 30.4 [95% CI, 29.0-31.8] x 10(3)/microL; P<.001). Factors independently associated with neurological involvement included past history of seizures (adjusted odds ratio [AOR], 3.50; 95% CI, 2.78-4.42), fever lasting 2 days or less (AOR, 2.02; 95% CI, 1.64-2.49), delayed capillary refill time (AOR, 3.66; 95% CI, 2.40-5.56), metabolic acidosis (AOR, 1.55; 95% CI, 1.29-1.87), and hypoglycemia (AOR, 2.11; 95% CI, 1.31-3.37). Mortality was higher in patients with neurological involvement (4.4% [95% CI, 4.2%-5.1%] vs 1.3% [95% CI, 1.1%-1.5%]; P<.001). At discharge, 159 (2.2%) of 7281 patients had neurological deficits.

CONCLUSIONS

Neurological involvement is common in children in Kenya with acute falciparum malaria, and is associated with metabolic derangements, impaired perfusion, parasitemia, and increased mortality and neurological sequelae. This study suggests that falciparum malaria exposes many African children to brain insults.

Assessing developmental outcomes in children from Kilifi, Kenya, following prophylaxis for seizures in cerebral malaria

The purpose of the study was to develop a culture-informed measure of developmental outcome and to apply it to detect differences in developmental level between children with cerebral malaria enrolled in a clinical trial to control seizures during the acute phase of the illness. The instrument was administered to a sample of 180 children, three and 12 months after discharge from hospital. The measure demonstrated high internal consistency, good inter-observer reliability, age sensitivity and strong relations with parental report of child functioning. No association was found between performance, or change in performance, with the prophylactic regime administered. The results suggested that the use of Phenobarbital in controlling provoked seizures has no observable effect on cognitive function.

Severe malaria in Cameroonian children: correlation between plasma levels of three soluble inducible adhesion molecules and TNF-alpha

Plasma levels of three soluble inducible adhesion molecules, namely: intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1) and endothelial leucocyte adhesion molecule-1 (sELAM-1) or sE-selectin and the pro-inflammatory cytokine, tumour necrosis factor-alpha (TNF-alpha) were measured in well-defined clinical groups of children with severe and uncomplicated malaria. The goal of the study was to investigate the role of these molecules in immunopathogenic processes associated with severe malaria in Cameroonian children. Results showed significantly increased plasma concentrations of sICAM-1, sVCAM-1 and sE-selectin in children with severe malaria compared to those with uncomplicated malaria and healthy children (P<0.001). TNF-alpha levels increased significantly in children with severe malaria, approximately 2-folds compared to those with uncomplicated malaria and about 3-folds compared to healthy children (P<0.001). More importantly, levels of TNF-alpha strongly correlated with those of the three adhesion molecules and were significantly associated with increased risk of death (P=0.03). In addition, children who died from severe malaria showed higher mean levels of all measured factors compared to those who recovered, with significant differences observed with sICAM-1 (P<0.001) and sE-selectin (P=0.002). Furthermore, children with severe malarial anemia relative to those without, showed significantly elevated levels of the three soluble molecules; and sICAM-1 was significantly associated with increased risk of severe anemia. Taken together, these results confirm the role of TNF-alpha and the three adhesion molecules in pathogenic processes associated with severe malaria in children, and suggest an association between sICAM-1 and severe malarial anemia.

CD4+ CD25+ regulatory T cells suppress CD4+ T-cell function and inhibit the development of Plasmodium berghei-specific TH1 responses involved in cerebral malaria pathogenesis

The infection of mice with Plasmodium berghei ANKA constitutes the best available mouse model for human Plasmodium falciparum-mediated cerebral malaria, a devastating neurological syndrome that kills nearly 2.5 million people every year. Experimental data suggest that cerebral disease results from the sequestration of parasitized erythrocytes within brain blood vessels, which is exacerbated by host proinflammatory responses mediated by cytokines and effector cells including T lymphocytes. Here, T cell responses to P. berghei ANKA were analyzed in cerebral malaria-resistant and -susceptible mouse strains. CD4+ T-cell proliferation and interleukin-2 (IL-2) production in response to parasite-specific and polyclonal stimuli were strongly inhibited in cerebral malaria-resistant mice. In vitro and in vivo depletion of CD4+ CD25+ regulatory T (T(reg)) cells significantly reversed the inhibition of CD4+ T-cell proliferation and IL-2 production, indicating that this cell population contributes to the suppression of T-cell function during malaria. Moreover, in vivo depletion of T(reg) cells prevented the development of parasite-specific TH1 cells involved in the induction of cerebral malaria during a secondary parasitic challenge, demonstrating a regulatory role for this cell population in the control of pathogenic responses leading to fatal disease.

Malarial retinopathy: a newly established diagnostic sign in severe malaria

Severe malaria is commonly misdiagnosed in Africa, leading to a failure to treat other life-threatening illnesses. In malaria-endemic areas, parasitemia does not ensure a diagnosis of severe malaria because parasitemia can be incidental to other concurrent disease. The detection of malarial retinopathy is a candidate diagnostic test for cerebral malaria. Malarial retinopathy consists of a set of retinal abnormalities that is unique to severe malaria and common in children with cerebral malaria. Its presence and severity are related to risk of death and length of coma in survivors. A large, prospective autopsy study of children dying with cerebral malaria in Malawi found that malarial retinopathy was better than any other clinical or laboratory feature in distinguishing malarial from non-malarial coma. However, visualization has to date relied on specialist examination techniques. Further studies are planned to evaluate the usefulness of funduscopy by general clinicians in a variety of settings across Africa. Studies of the retina and retinal blood vessels provide an unparalleled opportunity to visualize an infected microvasculature and its effect on neural tissue in vivo. This report reviews current knowledge of malarial retinopathy, including its use as a diagnostic test in the comatose child, and its value as a tool for research into the pathophysiology of cerebral malaria.

Adjuvant therapy in cerebral malaria

Cerebral malaria is the most common cause of non-traumatic encephalopathy in the world. The mainstay of therapy is either quinine or artemisinin, both of which are effective antimalarials. The clinical picture of cerebral malaria may persist or even become worse in spite of the clearance of parasites from blood. The death rate is unacceptably high even with effective antimalarials in tertiary care hospitals. The mortality increases in presence of multi organ failure (renal failure, jaundice, respiratory distress, severe anaemia, lactic acidosis, etc.). The pathogenesis of cerebral malaria is multifactorial and includes clogging, sequestration, rosette formation, release of cytokines, cerebral oedema, increased intracranial hypertension, etc. Attempts are made to use adjuvant therapy which will act through alternate mechanisms and address one or more of the pathogenetic processes. In this review, we have discussed the role of corticosteroids, pentoxifylline, desferrioxamine, mannitol and newer agents in the treatment of cerebral malaria. Though the literature on adjuvant therapy in cerebral malaria is large enough, there are a number of shortcomings in the clinical trials, many being open and non randomized or of very small sample size. Further research is of utmost importance through large multicentric, double-blind controlled trials to show the efficacy of any of these drugs.

von Willebrand factor propeptide in malaria: evidence of acute endothelial cell activation

The pathogenicity of Plasmodium falciparum is thought to relate to the unique ability of infected erythrocytes to adhere to and subsequently activate the vascular endothelium. To study the state of endothelial activation during falciparum malaria, we measured plasma levels of both von Willebrand factor (VWF) and its propeptide, indices of chronic and acute endothelial cell perturbation, respectively. Results were correlated with clinical and biochemical markers of disease severity, including plasma lactate. Our data show that acute endothelial cell activation is a hallmark of malaria in children, indicated by a significant rise in VWF and VWF propeptide. The highest VWF and propeptide levels were seen in cerebral and non-cerebral severe malaria, and associations found between VWF propeptide level and lactate (P < 0.001). Mean VWF propeptide levels (nmol/l) were in cerebral malaria 33.4, non-cerebral severe malaria 26.3, mild malaria 22.1, non-malaria febrile illness 10.2, and controls 10.1. Differences between patient and control groups were highly significant (P < 0.005). Follow-up of 26 cerebral malaria cases showed that levels of VWF propeptide, but not VWF fell by 24 h, following the clinical course of disease and recovery. These novel findings potentially implicate acute, regulated exocytosis of endothelial cell Weibel-Palade bodies in the pathogenesis of Plasmodium falciparum malaria.

Clusters of cytokines determine malaria severity in Plasmodium falciparum-infected patients from endemic areas of Central India

We investigated the role of interferon (IFN)- gamma , interleukin (IL)-1 beta , IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, tumor necrosis factor (TNF)- alpha , and transforming growth factor (TGF)- beta in clinically well-defined groups of Plasmodium falciparum-infected patients manifesting mild malaria (MM), severe noncerebral malaria (SM), or cerebral malaria (CM) and in control subjects from Gondia, a malaria-endemic site in India, as well as in healthy subjects from non-malaria-endemic areas. Two-way coupled cluster analysis revealed 2 clusters of cytokines relevant to clinical subgroups of disease. The first cluster was composed of IFN- gamma , IL-2, IL-5, IL-6, and IL-12, the levels of which were significantly increased during infection but were predominant in patients with MM and allowed us to distinguish them from patients with SM or CM. The second cluster was composed of TGF- beta , TNF- alpha , IL-10, and IL-1 beta , the levels of which were highly correlated with each other in the different clinical groups of patients and significantly increased with disease severity, particularly in CM. Discriminant analyses allowed us to propose a minimal model. Levels of cytokines such as IL-5, IL-1 beta , IL-10, and IL-2 increase with infection. Levels of IL-12, IL-5, and IL-6 discriminate severe forms of malaria from MM. Finally, levels of IL-1 beta , IL-12, and IFN- gamma are relevant for the discrimination of CM from SM: high IL-1 beta levels are associated with CM, and high IL-12 and IFN- gamma levels are associated with SM.

Behavioural and histopathological alterations in mice with cerebral malaria

Different features of sensorimotor function and behaviour were studied in murine cerebral malaria (CM) and malaria without cerebral involvement (non-CM) applying the primary screen of the SHIRPA protocol. Histopathological analysis of distinct brain regions was performed and the relative size of haemorrhages and plugging of blood cells to brain vasculature was analysed. Animals suffering from CM develop a wide range of behavioural and functional alterations in the progressive course of the disease with a statistically significant impairment in all functional categories assessed 36 h prior to death when compared with control animals. Early functional indicators of cerebral phenotype are impairments in reflex and sensory system and in neuropsychiatric state. Deterioration in function is paralleled by the degree of histopathological changes with a statistically significant correlation between the SHIRPA score of CM animals and the mean size of brain haemorrhage. Furthermore, image analysis yielded that the relative area of the brain lesions was significantly larger in the forebrain and brainstem compared with the other regions of interest. Our results indicate that assessment of sensory and motor tasks by the SHIRPA primary screen is appropriate for the early in vivo discrimination of cerebral involvement in experimental murine malaria. Our findings also suggest a correlation between the degree of functional impairment and the size of the brain lesions as indicated by parenchymal haemorrhage. Applying the SHIRPA protocol in the functional characterization of animals suffering from CM might prove useful in the preclinical assessment of new antimalarial and potential neuroprotective therapies.

Perforin mediated apoptosis of cerebral microvascular endothelial cells during experimental cerebral malaria

Cerebral malaria is a serious complication of Plasmodium falciparum infection. We have investigated the role of perforin in the pathogenesis of cerebral malaria in a murine model (Plasmodium berghei ANKA (PbA) infection). C57BL/6 mice demonstrated the typical neuropathological symptoms of experimental cerebral malaria infection from day 5p.i. and became moribund on day 6p.i. This pathology was not seen in PbA-infected, perforin-deficient (pfp-/-) mice. From days 5-6p.i. onwards there was a significant increase in mRNA for granzyme B and CD8, but not CD4, in brain tissue from PbA-infected C57BL/6 and pfp-/- mouse brains. Perforin mRNA was strongly increased in the brains of PbA-infected C57BL/6 mice on day 6p.i. Immunohistochemistry revealed increased perforin staining and elevated numbers of CD8(+) cells within the cerebral microvessels in PbA-infected C57BL/6 at days 5 and 6p.i. compared with uninfected animals. At day 6p.i., there were TUNEL-positive cells and activated caspase-3 positive cells of endothelial morphology in the CNS of PbA-infected C57BL/6 mice. The TUNEL-positive cells were greatly reduced in pfp-/- mice. These results suggest that CD8(+)T lymphocytes induce apoptosis of endothelial cells via a perforin-dependent process, contributing to the fatal pathogenic process in murine cerebral malaria.

Immunopathological consequences of the loss of engulfment genes: the case of ABCA1

Programmed cell death plays a crucial role in the maintenance of cell homeostasis. An initial, effector phase leads to the generation of apoptotic corpses and is closely followed by a swift clearance by professional or amateur phagocytes. Several aspects distinguish this latter process of engulfment of dying cells from the classical forms of phagocytosis. They concern all aspects of the process from the recognition of the prey to the final outcome, i.e. immunological silence. The engulfment of dead cells is a process highly conserved through evolution and it has been studied in parallel in two systems, mammalian cells and the nematode C. elegans. ABCA1 and its ortholog CED-7 in the nematode are key players of engulfment. Their mode of action is somehow original in the panorama of engulfment receptors since they act as lipid transporters. While in the worm the loss of CED-7 has phenotypic consequences exclusively on engulfment, in the mouse the deletion of ABCA1 by homologous recombination has highlighted broad consequences on macrophage biology. Among those we will discuss here the aberrant responses of ABCA1-/- mice to Plasmodium berghei ANKA infection, concerning in particular the development of cerebral malaria (CM), a cytokine-induced immunopathology. This syndrome involves a central role of monocytes and, as shown recently, high levels of circulating microparticles. It was found that ABCA1 loss completely protects against CM and its associated mortality. This observation, together with the demonstration of quantitative and functional modifications of microparticles, suggests that microparticles may be involved in CM pathogenesis. The ABCA1 transporter thus appears to control susceptibility to CM, thereby providing new insights in its pathophysiological mechanisms and potential new therapeutic avenues.

Cerebral malaria: role of microparticles and platelets in alterations of the blood-brain barrier

Brain lesions of cerebral malaria (CM) are characterised by a sequestration of Plasmodium falciparum-parasitised red blood cells (PRBC), leucocytes and platelets within brain microvessels, by an excessive release of pro-inflammatory cytokines as well as by disruption of the blood-brain barrier (BBB). We evaluated the possibility that PRBC and platelets interact and induce functional alterations in brain endothelium. Using an in vitro model of endothelial lesion, we showed that platelets can act as bridges between PRBC and endothelial cells (EC) allowing the binding of PRBC to endothelium devoid of cytoadherence receptors. Furthermore, platelets potentiated the cytotoxicity of PRBC for brain EC by inducing an alteration of the integrity of their monolayer and increasing their apoptosis. These findings provide insights into the mechanisms by which platelets can be deleterious to the brain endothelium during CM. Another aspect of inflammatory and infectious diseases is that they often lead to activation of vascular and blood cells. Such activation results in an enhanced vesiculation, i.e. the release of circulating microparticles (MP). We thus explored plasma levels of endothelial MP in Malawian children with malaria. Plasma MP numbers were markedly increased on admission only in patients with severe malaria complicated with coma. Using the experimental mouse model of CM, we evaluated the pathogenic implications of MP using genetically deficient mice in which the capacity to vesiculate is impaired. Such mice, lacking the ABCA-1 gene, upon infection by Plasmodium berghei ANKA, showed complete resistance to CM. When purified from infected susceptible animals, MP were able to reduce normal plasma clotting time and to significantly enhance tumour necrosis factor release from naïve macrophages. Altogether these data provide a novel insight into the pathogenic mechanisms leading to the neurological syndrome. The finding that ABCA-1 gene deletion confers complete protection against cerebral pathology, linked to an impaired MP production, provides new potential targets for therapeutic amelioration of severe malaria.

Human cerebral malaria and the blood-brain barrier

Malaria represents a continuing and major global health challenge and our understanding of how the Plasmodium parasite causes severe disease and death remains poor. One serious complication of the infection is cerebral malaria, a clinically complex syndrome of coma and potentially reversible encephalopathy, associated with a high mortality rate and increasingly recognised long-term sequelae in survivors. Research into the pathophysiology of cerebral malaria, using a combination of clinical and pathological studies, animal models and in vitro cell culture work, has focussed attention on the blood-brain barrier (BBB). This represents the key interface between the brain parenchyma and the parasite, which develops within an infected red cell but remains inside the vascular space. Studies of BBB function in cerebral malaria have provided some evidence for parasite-induced changes secondary to sequestration of parasitised red blood cells and host leukocytes within the cerebral microvasculature, such as redistribution of endothelial cell intercellular junction proteins and intracellular signaling. However, the evidence for a generalised increase in BBB permeability, leading to cerebral oedema, is conflicting. As well as direct cell adhesion-dependent effects, local adhesion-independent effects may activate and damage cerebral endothelial cells and perivascular cells, such as decreased blood flow, hypoxia or the effects of parasite toxins such as pigment. Finally, a number of systemic mechanisms could influence the BBB during malaria, such as the metabolic and inflammatory complications of severe disease acting 'at a distance'. This review will summarise evidence for these mechanisms from human studies of cerebral malaria and discuss the possible role for BBB dysfunction in this complex and challenging disease.

Imaging experimental cerebral malaria in vivo: significant role of ischemic brain edema

The first in vivo magnetic resonance study of experimental cerebral malaria is presented. Cerebral involvement is a lethal complication of malaria. To explore the brain of susceptible mice infected with Plasmodium berghei ANKA, multimodal magnetic resonance techniques were applied (imaging, diffusion, perfusion, angiography, spectroscopy). They reveal vascular damage including blood-brain barrier disruption and hemorrhages attributable to inflammatory processes. We provide the first in vivo demonstration for blood-brain barrier breakdown in cerebral malaria. Major edema formation as well as reduced brain perfusion was detected and is accompanied by an ischemic metabolic profile with reduction of high-energy phosphates and elevated brain lactate. In addition, angiography supplies compelling evidence for major hemodynamics dysfunction. Actually, edema further worsens ischemia by compressing cerebral arteries, which subsequently leads to a collapse of the blood flow that ultimately represents the cause of death. These findings demonstrate the coexistence of inflammatory and ischemic lesions and prove the preponderant role of edema in the fatal outcome of experimental cerebral malaria. They improve our understanding of the pathogenesis of cerebral malaria and may provide the necessary noninvasive surrogate markers for quantitative monitoring of treatment.

Cerebral malaria is associated with IgG2 and IgG4 antibody responses to recombinant Plasmodium falciparum RIFIN antigen

RIFIN proteins belong to the largest Plasmodium falciparum multicopy family of variant surface antigens (VSA) expressed by infected erythrocytes. VSA antibodies have been shown to be associated with protection against malaria. Here, antibody subclass responses to a recombinant RIFIN protein (RIF-29) in 116 Ghanaian children were determined by ELISA to investigate the relationship between severe malaria and anti-RIF-29 antibodies. The study group was composed of 23 children diagnosed exclusively for cerebral malaria and 35 children who had non-cerebral severe malaria. The remaining 58 individuals were age-, gender- and area-matched asymptomatic controls. The finding that IgG1 and IgG3 responses predominated in severe malaria patients compared to matched controls suggests that these antibodies are not protective, but are most probably induced by a current infection, an observation substantiated by the equally high reactivity to both recombinant RIF-29 protein and to P. falciparum crude lysate proteins. The exclusive detection of IgG2 and IgG4 antibodies to RIF-29 protein only in cerebral malaria children brings to mind the possibility that these antibodies are pathogenic. This is a new finding that may go some way towards explaining why these children are at risk of developing the life-threatening form of cerebral malaria.

Pathogenesis, clinical features, and neurological outcome of cerebral malaria

Cerebral malaria is the most severe neurological complication of Plasmodium falciparum malaria. Even though this type of malaria is most common in children living in sub-Saharan Africa, it should be considered in anybody with impaired consciousness that has recently travelled in a malaria-endemic area. Cerebral malaria has few specific features, but there are differences in clinical presentation between African children and non-immune adults. Subsequent neurological impairments are also most common and severe in children. Sequestration of infected erythrocytes within cerebral blood vessels seems to be an essential component of the pathogenesis. However, other factors such as convulsions, acidosis, or hypoglycaemia can impair consciousness. In this review, we describe the clinical features and epidemiology of cerebral malaria. We highlight recent insights provided by ex-vivo work on sequestration and examination of pathological specimens. We also summarise recent studies of persisting neurocognitive impairments in children who survive cerebral malaria and suggest areas for further research.

Blood-brain barrier breakdown during cerebral malaria: suicide or murder?

Cerebral malaria, one of the most serious complications of Plasmodium falciparum infection, is characterized by the sequestration of parasitized red blood cells (PRBCs) in cerebral microvascular beds. The precise mechanisms involved in the onset of neuropathology remain unknown, but parasite sequestration in the brain, metabolic disturbances, and host immune responses all play a role. Sequestration of PRBCs is mediated by different endothelial cell surface receptors, mainly ICAM-1 and CD36. In vitro studies demonstrated that PRBC adhesion to endothelial cells induces over-expression of various adhesion molecules including ICAM-1, expression of iNOS, oxidative stress and finally apoptosis in endothelial cells. In vivo studies, in humans and in mice models of cerebral malaria brought striking evidence of the implication of brain infiltrating cytotoxic effector CD8T lymphocytes in the development of murine cerebral malaria pathogenesis. These cells probably act by direct cytotoxicity against endothelial cells. Cytotoxicity and apoptosis potentially lead blood-brain-barrier disruption and could contribute to the development of cerebral malaria. We propose a key role for endothelial cells in the pathogenesis of cerebral malaria, both by suicide / apoptosis, and / or by murder / cytotoxicity.

Cerebral malaria -- a neurovascular pathology with many riddles still to be solved

Cerebral malaria (CM), one of the most common fatal complications of the heterogenous syndrome named severe malaria, is indubitably a post-infectious neurovascular pathology, as evidenced by histopathological analyses. This neurological syndrome is characterised not only by the cytoadherence of Plasmodium falciparum-infected erythrocytes, but also by morphological and functional alterations of brain microvascular endothelial cells subsequent to their interactions with circulating cells, such as platelets, monocytes, lymphocytes, and dendritic cells. During CM, host cells, in particular immune cells, are found recruited and activated at the site of sequestration, where they release various soluble molecules. Among these, cytokines play a major role in CM pathogenesis. Indeed, cerebral complications appear to be due to an imbalance between pro-inflammatory and anti-inflammatory mediators. Cytokines (notably interferon-gamma, tumour necrosis factor, lymphotoxin) and chemokine receptors (notably CCR5) are also responsible for blood-brain barrier alterations and biochemical changes leading to the brain parenchymal lesions that can be observed in CM. In return, glial cells can influence blood-borne elements, and thereby worsen the pathology. Numerous problems remain to be solved, especially the sequence of pathological events, namely the order in which the circulating cells sequester on the endothelial wall. A better understanding of the molecular mechanisms involved in CM pathogenesis is needed if we are capable of preventing cerebral complications and improving the quality of patient management.

Species-specific inhibition of cerebral malaria in mice coinfected with Plasmodium spp

Recent epidemiological observations suggest that clinical evolution of Plasmodium falciparum infections might be influenced by the concurrent presence of another Plasmodium species, and such mixed-species infections are now known to occur frequently in residents of most areas of endemicity. We used mice infected with P. berghei ANKA (PbA), a model for cerebral malaria (CM), to investigate the influence of experimental mixed-species infections on the expression of this pathology. Remarkably, the development of CM was completely inhibited by the simultaneous presence of P. yoelii yoelii but not that of P. vinckei or another line of P. berghei. In the protected coinfected mice, the accumulation of CD8(+) T cells in the brain vasculature, a pivotal step in CM pathogenesis, was found to be abolished. Protection from CM was further found to be associated with species-specific suppression of PbA multiplication. These observations establish the concept of mixed Plasmodium species infections as potential modulators of pathology and open novel avenues to investigate mechanisms implicated in the pathogenesis of malaria.