Infectious diseases of the nervous system and their impact in developing countries

The influence of fixation and cryopreservation of cerebrospinal fluid on antigen expression and cell percentages by flow cytometric analysis

The pauci-cellular nature of cerebrospinal (CSF), particularly ventricular CSF, and the rapid cell death following sampling, incumbers the use of flow cytometric analysis of these samples in the investigation of central nervous system (CNS) pathologies. Developing a method that allows long-term storage and batched analysis of CSF samples without compromising cell integrity is highly desirable in clinical research, given that CSF is often sampled after hours creating logistical difficulties for fresh processing. We examined percentages and relative proportion of peripheral and brain-derived immune cells in cryopreserved and transfix-treated CSF, compared to freshly processed CSF. Cell proportions were more comparable between Fresh and Cryopreserved CSF (mean of differences = 3.19), than between fresh and transfix-treated CSF (mean of differences = 14.82). No significant differences in cell percentages were observed in fresh versus cryopreserved CSF; however significantly lower cell percentages were observed in transfix-treated CSF compared to Fresh CSF [(CD11b++ (p = 0.01), CD4+ (p = 0.001), CD8+ (p = 0.007), NK cells (p = 0.04), as well as CD69+ activation marker (p = 0.001)]. Furthermore, loss of marker expression of various lymphocyte sub-populations were observed in transfix-treated CSF. Cryopreservation is a feasible option for long-term storage of ventricular CSF and allows accurate immunophenotyping of peripheral and brain-derived cell populations by flow cytometry.

Purinergic signaling in infectious diseases of the central nervous system

The incidence of infectious diseases affecting the central nervous system (CNS) has been increasing over the last several years. Among the reasons for the expansion of these diseases and the appearance of new neuropathogens are globalization, global warming, and the increased proximity between humans and wild animals due to human activities such as deforestation. Neurotropism affecting normal brain function is shared by organisms such as viruses, bacteria, fungi, and parasites. Neuroinfections caused by these agents activate immune responses, inducing neuroinflammation, excitotoxicity, and neurodegeneration. Purinergic signaling is an evolutionarily conserved signaling pathway associated with these neuropathologies. During neuroinfections, host cells release ATP as an extracellular danger signal with pro-inflammatory activities. ATP is metabolized to its derivatives by ectonucleotidases such as CD39 and CD73; ATP and its metabolites modulate neuronal and immune mechanisms through P1 and P2 purinergic receptors that are involved in pathophysiological mechanisms of neuroinfections. In this review we discuss the beneficial or deleterious effects of various components of the purinergic signaling pathway in infectious diseases that affect the CNS, including human immunodeficiency virus (HIV-1) infection, herpes simplex virus type 1 (HSV-1) infection, bacterial meningitis, sepsis, cryptococcosis, toxoplasmosis, and malaria. We also provide a description of this signaling pathway in emerging viral infections with neurological implications such as Zika and SARS-CoV-2.

The health burden of non-communicable neurological disorders in the USA between 1990 and 2017

In this observational study, using the Global Burden of Disease and Risk Factors Study, we aimed to (i) report the magnitude of health loss due to non-communicable neurological disorders in the USA in 2017 by sex, age, years and States and (ii) to identify non-communicable neurological disorders attributable environmental, metabolic and behavioural risk factors. We provide estimates of the burden of non-communicable neurological disorders by reporting disability-adjusted life-years and their trends from 1990 to 2017 by age and sex in the USA. The non-communicable neurological disorders include migraines, tension-type headaches, multiple sclerosis, Alzheimer's disease and other dementias, Parkinson's disease, epilepsy, motor neuron diseases and other neurological disorders. In 2017, the global burdens of non-communicable neurological disorders were 1444.41 per 100 000, compared to the USA burden of 1574.0. Migraine was the leading age-standardized disability-adjusted life-years 704.7 per 100 000, with Alzheimer's disease and other dementias (41.8.7), and epilepsy (123.8) taking the second and third places, respectively. Between 1990 and 2017, the age-standardized disability-adjusted life-years rates for aggregate non-communicable neurological disorders relative to all cause increased by 3.42%. More specifically, this value for motor neuron diseases, Parkinson's disease and multiple sclerosis increase by 20.9%, 4.0%, 2.47%, 3.0% and 1.65%, respectively. In 2017, the age-standardized disability-adjusted life-years rates for the aggregate non-communicable neurological disorders was significantly higher in females than the males (1843.5 versus 1297.3 per 100 000), respectively. The age-standardized disability-adjusted life-years rates for migraine were the largest in both females (968.8) and males were (432.5) compared to other individual non-communicable neurological disorders. In the same year, the leading non-communicable neurological disorders age-standardized disability-adjusted life-years rates among children ≤9 was epilepsy (216.4 per 100 000). Among the adults aged 35-60 years, it was migraine (5792.0 per 100 000), and among the aged 65 and above was Alzheimer's disease and other dementias (78 800.1 per 100 000). High body mass index, smoking, high fasting plasma glaucous and alcohol use were the attributable age-standardized disability-adjusted life-years risks for aggregate and individual non-communicable neurological disorders. Despite efforts to decrease the burden of non-communicable neurological disorders in the USA, they continue to burden the health of the population. Children are most vulnerable to epilepsy-related health burden, adolescents and young adults to migraine, and elderly to Alzheimer's disease and other dementias and epilepsy. In all, the most vulnerable populations to non-communicable neurological disorders are females, young adults and the elderly.

Validation of diffusion measurements obtained on a 0.35T MR in Malawi: Important insights for radiologists in low income settings with low field MRI

PURPOSE

To investigate the reliability of diffusion weighted image (DWI) measurements obtained on a 0.35T MR scanner in Malawi for malaria research.

MATERIALS AND METHODS

The same healthy volunteers (n=6) were scanned on a 0.35T MR scanner in Malawi and a 3T scanner in the US. Three subjects had two repeated DWI scans at 0.35T. Due to scanner constraints, only three diffusion gradient directions for DWI on 0.35T could be obtained. An apparent diffusion coefficient (ADC) map was reconstructed from the 0.35T and the result was compared to standard DWI acquisition on the 3T scanner. The mean ADC from 15 different regions and the voxel-wise coefficient of variation (CV) were calculated to investigate the intra-scanner and inter-scanner variability. Reproducibility was calculated using intra-class correlation coefficient (ICC).

RESULTS

The 0.35T intra-scanner ADC repeatability was high for all three subjects with repeated scans (ICC>0.7). The intra-scanner correlation between repeated scans was also high (r>0.67, p< 0.01). Comparing the ADC findings from the 0.35T and 3T MRs, the high inter-scanner correlation suggested that the 0.35T ADC results were valid (ICC>0.7, r>0.5, p<0.01). Voxel-wise CV revealed a few regions with larger variation (CV>20%), which were primarily located in peripheral regions and the boundary of lateral ventricles, and likely due to partial volume effects in low field scans.

CONCLUSION

These findings support the validity of DWI obtained from low field MR scanners used in many low income countries.

African trypanosomes and brain infection - the unsolved question

African trypanosomes induce sleeping sickness. The parasites are transmitted during the blood meal of a tsetse fly and appear primarily in blood and lymph vessels, before they enter the central nervous system. During the latter stage, trypanosomes induce a deregulation of sleep-wake cycles and some additional neurological disorders. Historically, it was assumed that trypanosomes cross the blood-brain barrier and settle somewhere between the brain cells. The brain, however, is a strictly controlled and immune-privileged area that is completely surrounded by a dense barrier that covers the blood vessels: this is the blood-brain barrier. It is known that some immune cells are able to cross this barrier, but this requires a sophisticated mechanism and highly specific cell-cell interactions that have not been observed for trypanosomes within the mammalian host. Interestingly, trypanosomes injected directly into the brain parenchyma did not induce an infection. Likewise, after an intraperitoneal infection of rats, Trypanosoma brucei brucei was not observed within the brain, but appeared readily within the cerebrospinal fluid (CSF) and the meninges. Therefore, the parasite did not cross the blood-brain barrier, but the blood-CSF barrier, which is formed by the choroid plexus, i.e. the part of the ventricles where CSF is produced from blood. While there is no question that trypanosomes are able to invade the brain to induce a deadly encephalopathy, controversy exists about the pathway involved. This review lists experimental results that support crossing of the blood-brain barrier and of the blood-CSF barrier and discuss the implications that either pathway would have on infection progress and on the survival strategy of the parasite. For reasons discussed below, we prefer the latter pathway and suggest the existence of an additional distinct meningeal stage, from which trypanosomes could invade the brain via the Virchow-Robin space thereby bypassing the blood-brain barrier. We also consider healthy carriers, i.e. people living symptomless with the disease for up to several decades, and discuss implications the proposed meningeal stage would have for new anti-trypanosomal drug development. Considering the re-infection of blood, a process called relapse, we discuss the likely involvement of the newly described glymphatic connection between the meningeal space and the lymphatic system, that seems also be important for other infectious diseases.

Chikungunya alphavirus infection in the nervous system and possible mechanisms of pathogenesis

Chikungunya alphavirus (CHIKV) is transmitted by mosquitoes. Recent worldwide epidemics have revealed that CHIKV infects mainly muscles and joint tissues. Patients will suffer from arthralgia from months to years and leading to chronic arthritis. While CHIKV neuroinfection of susceptible hosts such as neonates is rare, it can lead to severe meningoencephalitis and encephalitis. CHIKV preferentially targets astrocytes, ependymal cells as well as epithelial cells of the choroid plexus. Remarkably, neurons are relatively spared but could suffer from the inflammatory response mounted by glial cells and recruited leukocytes. Interferon and related molecules as well as apoptosis will control the infectious challenge. Protective measures are critically needed and involving vaccination or passive immunization particularly in areas at risk of emerging epidemics.

Pediatric cerebral malaria: a scourge of Africa

Cerebral malaria, defined as an otherwise unexplained coma in a patient with Plasmodium falciparum parasitemia, affects up to 1 million people per year, the vast majority of them being children living in sub-Saharan Africa. Despite optimal treatment, this condition kills 15% of those affected and leaves 30% of survivors with neurologic sequelae. The clinical diagnosis is hampered by its poor specificity, but the presence or absence of a malarial retinopathy in cerebral malaria has proven to be important in the differentiation of underlying coma etiology. Both antimalarials and intense supportive care are necessary for optimal treatment. As of yet, clinical trials of adjunctive therapies have not improved the high rates of mortality and morbidity. Survivors are at high risk of neurologic sequelae including epilepsy, neurodisabilities and cognitive–behavioral problems. The neuroanatomic and functional bases of these sequelae are being elucidated. Although adjunctive therapy trials continue, the best hope for African children may lie in disease prevention. Strategies include bednets, chemoprophylaxis and vaccine development.

In vitro and in vivo activities of 2-aminopyrazines and 2-aminopyridines in experimental models of human African trypanosomiasis

New drugs for the treatment of human African trypanosomiasis are urgently needed. A number of 2-aminopyrazines/2-aminopyridines were identified as promising leads following a focused screen of 5,500 compounds for Trypanosoma brucei subsp. brucei viability. Described compounds are trypanotoxic in the submicromolar range and show comparably low cytotoxicity on representative mammalian cell lines. Specifically, 6-([6-fluoro-3,4-dihydro-2H-1-benzopyran-4-yl)]oxy)-N-(piperidin-4-yl)pyrazin-2-amine (CBK201352) is trypanotoxic for T. brucei subsp. brucei, T. brucei subsp. gambiense, and T. brucei subsp. rhodesiense and is nontoxic to mammalian cell lines, and in vitro preclinical assays predict promising pharmacokinetic parameters. Mice inoculated intraperitoneally (i.p.) with 25 mg/kg CBK201352 twice daily for 10 days, starting on the day of infection with T. brucei subsp. brucei, show complete clearance of parasites for more than 90 days. Thus, CBK201352 and related analogs are promising leads for the development of novel treatments for human African trypanosomiasis.

Infectious causes of seizures and epilepsy in the developing world

Central nervous system (CNS) infections are the main cause of seizures and acquired epilepsy in the developing world. Geographical variations determine the common causes in a particular region. Acute seizures are common in severe meningitis, viral encephalitis, malaria, and neurocysticercosis, and in most cases are associated with increased mortality and morbidity, including subsequent epilepsy. Neuronal excitability secondary to proinflammatory signals induced by CNS infections are an important common mechanism for the generation of seizures, in addition to various other specific mechanisms. Newer insights into the neurobiology of these infections and the associated epilepsy could help in developing neuroprotective interventions. Management issues include prompt treatment of acute seizures and the underlying CNS infection, correction of associated predisposing factors, and decisions regarding the appropriate choice and duration of antiepileptic therapy. Strategies for the prevention of epilepsy in CNS infections such as early anti-infective and anti-inflammatory therapy need scientific exploration. Prevention of CNS infections is the only definitive way forward to reduce the burden of epilepsy in developing countries.

Alterations in the Brain Transcriptome in Plasmodium Berghei ANKA Infected Mice

We have used cDNA microarrays to compare gene expression profiles in brains from normal mice to those infected with the ANKA strain of Plasmodium berghei, a model of cerebral malaria. For each of three brains in each group, we computed ratios of all quantifiable genes with a composite reference sample and then computed ratios of gene expression in infected brains compared to untreated controls. Of the almost 12,000 unigenes adequately quantified in all arrays, approximately 3% were significantly downregulated (P < 0.05, ≥ 50% fold change) and about 7% were upregulated. Upon inspection of the lists of regulated genes, we identified a high number encoding proteins of importance to normal brain function or associated with neuropathology, including genes that encode for synaptic proteins or genes involved in cerebellar function as well as genes important in certain neurological diseases such as Alzheimer's disease or autism. These results emphasize the important impact of malarial infection on gene expression in the brain and provide potential biomarkers that may provide novel therapeutic targets to ameliorate the neurological sequelae of this infection.

Neuroinflammation and brain infections: historical context and current perspectives

An overview of current concepts on neuroinflammation and on the dialogue between neurons and non-neuronal cells in three important infections of the central nervous systems (rabies, cerebral malaria, and human African trypanosomiasis or sleeping sickness) is here presented. Large numbers of cases affected by these diseases are currently reported. In the context of an issue dedicated to Camillo Golgi, historical notes on seminal discoveries on these diseases are also presented. Neuroinflammation is currently closely associated with pathogenetic mechanisms of chronic neurodegenerative diseases. Neuroinflammatory signaling in brain infections is instead relatively neglected in the neuroscience community, despite the fact that the above infections provide paradigmatic examples of alterations of the intercellular crosstalk between neurons and non-neuronal cells. In rabies, strategies of immune evasion of the host lead to silencing neuroinflammatory signaling. In the intravascular pathology which characterizes cerebral malaria, leukocytes and Plasmodium do not enter the brain parenchyma. In sleeping sickness, leukocytes and African trypanosomes invade the brain parenchyma at an advanced stage of infection. Both the latter pathologies leave open many questions on the targeting of neuronal functions and on the pathogenetic role of non-neuronal cells, and in particular astrocytes and microglia, in these diseases. All three infections are hallmarked by very severe clinical pictures and relative sparing of neuronal structure. Multidisciplinary approaches and a concerted action of the neuroscience community are needed to shed light on intercellular crosstalk in these dreadful brain diseases. Such effort could also lead to new knowledge on non-neuronal mechanisms which determine neuronal death or survival.