Human herpesvirus-6 entry into the central nervous system through the olfactory pathway

Sensory Dysfunction, Microbial Infections, and Host Responses in Alzheimer's Disease

Sensory functions of organs of the head and neck allow humans to interact with the environment and establish social bonds. With aging, smell, taste, vision, and hearing decline. Evidence suggests that accelerated impairment in sensory abilities can reflect a shift from healthy to pathological aging, including the development of Alzheimer's disease (AD) and other neurological disorders. While the drivers of early sensory alteration in AD are not elucidated, insults such as trauma and infections can affect sensory function. Herein, we review the involvement of the major head and neck sensory systems in AD, with emphasis on microbes exploiting sensory pathways to enter the brain (the "gateway" hypothesis) and the potential feedback loop by which sensory function may be impacted by central nervous system infection. We emphasize detection of sensory changes as first-line surveillance in senior adults to identify and remove potential insults, like microbial infections, that could precipitate brain pathology.

Symptomatic central nervous system tuberculosis and human herpesvirus-6 coinfection with associated hydrocephalus managed with endoscopic third ventriculostomy: A case report and review of human herpesvirus-6 neuropathology

Background

Human herpesvirus 6 (HHV-6) is a double-stranded DNA virus well established in the clinical literature to cause the near-universal childhood infection roseola infantum (exanthema subitum/sixth disease). Primary HHV-6 infection has been reported to cause meningoencephalitis in pediatric patients, although generally in the immunocompromised.

Case Description

The authors treated an immunocompetent 18-month-old female who transferred to our institution for a higher level of care given concerns for meningitis in the setting of decreased level of arousal (Glasgow Coma Scale 12), and bradycardia 9 days after the onset of nasal congestion, fatigue, and repeated bouts of emesis. Outside hospital cerebrospinal fluid (CSF) studies were notable for hypoglycorrhachia, elevated protein, elevated nucleated cells with a mononuclear predominance, and a meningitis polymerase chain reaction panel that was positive only for HHV-6. Brain magnetic resonance imaging with and without contrast revealed a basal cistern predominant leptomeningeal enhancement pattern as well as moderate ventriculomegaly with associated periventricular edema concerning acute communicating hydrocephalus. Considering the CSF studies, neuroimaging, and recent travel history to Mexico, central nervous system (CNS) tuberculosis (TB) was the leading suspicion, and antimicrobial therapy was initiated for this presumptive diagnosis with culture data only proving the TB suspicion correct after nearly 2 months in culture. Anti-viral therapy was initially not felt to be necessary as the HHV-6 was interpreted as incidental and not a cause of symptomatic meningitis in our immunocompetent host. The patient's hydrocephalus was treated with temporary CSF diversion followed by performance of an endoscopic third ventriculostomy. Despite appropriate hydrocephalus management, clinical improvement ultimately seemed to correlate with the initiation of antiviral therapy.

Conclusion

The authors present this case and review the literature on HHV-6-associated CNS infections with the goal of informing the neurosurgeon about this often clinically underestimated pathogen.

The hidden link: How oral and respiratory microbiomes affect multiple sclerosis

BACKGROUND

Extensive research has explored the role of gut microbiota in multiple sclerosis (MS). However, the impact of microbial communities in the oral cavity and respiratory tract on MS is an emerging area of investigation.

PURPOSE

We aimed to review the current literature related to the nasal, oral, and lung microbiota in people with MS (PwMS).

METHODS

We conducted a narrative review of clinical and preclinical original studies on PubMed that explored the relationship between the bacterial or viral composition of the nasal, lung, and oral microbiota and MS. Additionally, to find relevant studies not retrieved initially, we also searched for references in related review papers, as well as the references cited within the included studies.

RESULTS AND CONCLUSIONS

Thirteen studies were meticulously reviewed in three sections; oral microbiota (n = 8), nasal microbiota (n = 3), and lung microbiota (n = 2), highlighting considerable alterations in the oral and respiratory microbiome of PwMS compared to healthy controls (HCs). Genera like Aggregatibacter and Streptococcus were less abundant in the oral microbiota of PwMS compared to HCs, while Staphylococcus, Leptotrichia, Fusobacterium, and Bacteroides showed increased abundance in PwMS. Additionally, the presence of specific bacteria, including Streptococcus sanguinis, within the oral microbiota was suggested to influence Epstein-Barr virus reactivation, a well-established risk factor for MS. Studies related to the nasal microbiome indicated elevated levels of specific Staphylococcus aureus toxins, as well as nasal glial cell infection with human herpes virus (HHV)-6 in PwMS. Emerging research on lung microbiome in animal models demonstrated that manipulating the lung microbiome towards lipopolysaccharide-producing bacteria might suppress MS symptoms. These findings open avenues for potential therapeutic strategies. However, further research is crucial to fully understand the complex interactions between the microbiome and MS. This will help identify the most effective timing, bacterial strains, and modulation techniques.

Olfactory immunology: the missing piece in airway and CNS defence

The olfactory mucosa is a component of the nasal airway that mediates the sense of smell. Recent studies point to an important role for the olfactory mucosa as a barrier to both respiratory pathogens and to neuroinvasive pathogens that hijack the olfactory nerve and invade the CNS. In particular, the COVID-19 pandemic has demonstrated that the olfactory mucosa is an integral part of a heterogeneous nasal mucosal barrier critical to upper airway immunity. However, our insufficient knowledge of olfactory mucosal immunity hinders attempts to protect this tissue from infection and other diseases. This Review summarizes the state of olfactory immunology by highlighting the unique immunologically relevant anatomy of the olfactory mucosa, describing what is known of olfactory immune cells, and considering the impact of common infectious diseases and inflammatory disorders at this site. We will offer our perspective on the future of the field and the many unresolved questions pertaining to olfactory immunity.

Herpesvirus Infection of Endothelial Cells as a Systemic Pathological Axis in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Understanding the pathophysiology of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is critical for advancing treatment options. This review explores the novel hypothesis that a herpesvirus infection of endothelial cells (ECs) may underlie ME/CFS symptomatology. We review evidence linking herpesviruses to persistent EC infection and the implications for endothelial dysfunction, encompassing blood flow regulation, coagulation, and cognitive impairment-symptoms consistent with ME/CFS and Long COVID. This paper provides a synthesis of current research on herpesvirus latency and reactivation, detailing the impact on ECs and subsequent systemic complications, including latent modulation and long-term maladaptation. We suggest that the chronicity of ME/CFS symptoms and the multisystemic nature of the disease may be partly attributable to herpesvirus-induced endothelial maladaptation. Our conclusions underscore the necessity for further investigation into the prevalence and load of herpesvirus infection within the ECs of ME/CFS patients. This review offers conceptual advances by proposing an endothelial infection model as a systemic mechanism contributing to ME/CFS, steering future research toward potentially unexplored avenues in understanding and treating this complex syndrome.

Identification of a strong genetic risk factor for major depressive disorder in the human virome

The heritability of major depressive disorder (MDD) is reportedly 30-50%. However, the genetic basis of its heritability remains unknown. Within SITH-1, a risk factor for MDD in human herpesvirus 6B (HHV-6B), we discovered a gene polymorphism with a large odds ratio for an association with MDD. It was a sequence whose number of repeats was inversely correlated with SITH-1 expression. This number was significantly lower in MDD patients. Rates for 17 or fewer repeats of the sequence were 67.9% for MDD and 28.6% for normal controls, with an odds ratio of 5.28. For patients with 17 or less repeats, the rate for presence of another MDD patient in their families was 47.4%, whereas there were no MDD patients in the families of patients with more than 17 repeats. Since HHV-6B is transmitted primarily mother to child and within families and persists for life, this gene polymorphism could potentially influence heritability of MDD.

Infectious leukoencephalopathies

Leukoencephalopathy from infectious agents may have a rapid course, such as human simplex virus encephalitis; however, in many diseases, it may take months or years before diagnosis, such as in subacute sclerosing panencephalitis or Whipple disease. There are wide geographic distributions and susceptible populations, including both immunocompetent and immunodeficient patients. Many infections have high mortality rates, such as John Cunningham virus and subacute sclerosing panencephalitis, although others have effective treatments if suspected and treated early, such as herpes simplex encephalitis. This chapter will describe viral, bacterial, and protozoal infections, which predominantly cause leukoencephalopathy. We focus on the clinical presentation of these infectious agents briefly covering epidemiology and subtypes of infections. Next, we detail current pathophysiologic mechanisms causing white matter injury. Diagnostic and confirmatory tests are discussed. We cover predominantly MRI imaging features of leukoencephalopathies, and in addition, summarize the common imaging features. Additionally, we detail how imaging features may be used to narrow the differential of a leukoencephalopathy clinical presentation. Lastly, we present an outline of common treatment approaches where available.

Human Herpes Virus 6-Associated Meningitis in an Immunocompetent Adult With a History of Plaque Psoriasis: A Case Report

Human herpes virus-6 (HHV-6) is a common cause of viral infection in humans, recognized for causing exanthema subitem during the first two years of life. Chronic inflammatory states in different autoimmune diseases can be associated with an immunosuppressed microenvironment. We report a case of HHV-6-associated meningitis in a patient with psoriasis. A 36-year-old man with a history of psoriasis presented with worsening bifrontal headache as well as painful oral lesions on the tongue and soft palate. Computed tomographic (CT) scan of the brain was nondiagnostic. Cerebrospinal fluid (CSF) analysis was diagnostic for HHV-6 infection and was treated with intravenous ganciclovir for two weeks. This case report highlights the emergence of HHV-6 infections in people with underlying mild immune disorders, such as psoriasis. Plaque psoriasis, such as in this patient, could be related to viral infections not typically seen among adults.

The viral hypothesis in Alzheimer's disease: SARS-CoV-2 on the cusp

Increasing evidence highlights that infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has long-term effects on cognitive function, which may cause neurodegenerative diseases like Alzheimer's disease (AD) in the future. We performed an analysis of a possible link between SARS-CoV-2 infection and AD risk and proposed several hypotheses for its possible mechanism, including systemic inflammation, neuroinflammation, vascular endothelial injury, direct viral infection, and abnormal amyloid precursor protein metabolism. The purpose of this review is to highlight the impact of infection with SASR-CoV-2 on the future risk of AD, to provide recommendations on medical strategies during the pandemic, and to propose strategies to address the risk of AD induced by SASR-CoV-2. We call for the establishment of a follow-up system for survivors to help researchers better understand the occurrence, natural history, and optimal management of SARS-CoV-2-related AD and prepare for the future.

Viral Nucleases from Herpesviruses and Coronavirus in Recombination and Proofreading: Potential Targets for Antiviral Drug Discovery

In this review, we explore recombination in two very different virus families that have become major threats to human health. The Herpesviridae are a large family of pathogenic double-stranded DNA viruses involved in a range of diseases affecting both people and animals. Coronaviridae are positive-strand RNA viruses (CoVs) that have also become major threats to global health and economic stability, especially in the last two decades. Despite many differences, such as the make-up of their genetic material (DNA vs. RNA) and overall mechanisms of genome replication, both human herpes viruses (HHVs) and CoVs have evolved to rely heavily on recombination for viral genome replication, adaptation to new hosts and evasion of host immune regulation. In this review, we will focus on the roles of three viral exonucleases: two HHV exonucleases (alkaline nuclease and PolExo) and one CoV exonuclease (ExoN). We will review the roles of these three nucleases in their respective life cycles and discuss the state of drug discovery efforts against these targets.

The Role of Human Herpesvirus 6 Infection in Alzheimer’s Disease Pathogenicity—A Theoretical Mosaic

Alzheimer’s disease (AD), a neurodegenerative disorder generally affecting older adults, is the most common form of dementia worldwide. The disease is marked by severe cognitive and psychiatric decline and has dramatic personal and social consequences. Considerable time and resources are dedicated to the pursuit of a better understanding of disease mechanisms; however, the ultimate goal of obtaining a viable treatment option remains elusive. Neurodegenerative disease as an outcome of gene–environment interaction is a notion widely accepted today; a clear understanding of how external factors are involved in disease pathogenesis is missing, however. In the case of AD, significant effort has been invested in the study of viral pathogens and their role in disease mechanisms. The current scoping review focuses on the purported role HHV-6 plays in AD pathogenesis. First, early studies demonstrating evidence of HHV-6 cantonment in either post-mortem AD brain specimens or in peripheral blood samples of living AD patients are reviewed. Next, selected examples of possible mechanisms whereby viral infection can directly or indirectly contribute to AD pathogenesis are presented, such as autophagy dysregulation, the interaction between miR155 and HHV-6, and amyloid-beta as an antimicrobial peptide. Finally, closely related topics such as HHV-6 penetration in the CNS, HHV-6 involvement in neuroinflammation, and a brief discussion on HHV-6 epigenetics are examined.

Dynamics of salivary human herpesvirus-6 and -7 shedding in pregnant women

OBJECTIVES

Reactivation of Betaherpesvirinae (Human herpesvirus 6A: HHV-6A, -6B, HHV-7) may be associated with mental illness and host fatigue. This study aimed to determine whether viral reactivation, measured by monitoring salivary viral DNA load, can be used to monitor depression in pregnant and postpartum women.

METHODS

Saliva samples were collected from 64 pregnant women at five-point of observation periods. The HHV-6 and HHV-7 specific qPCRs were carried out to measure viral DNA load. When HHV-6 DNA was detected in saliva, nested PCR was used to discriminate between HHV-6A and B.

RESULTS

In both viruses, a significant correlation was observed between detection frequency and viral DNA load in saliva. In the low-shedding group, HHV-6 DNA was significantly higher in the third trimester (P<0.0001), the time of delivery (P=0.0003), one month after birth (P=0.0023) compared to the first trimester, and HHV-7 was at the time of delivery (P=0.0277) and one month after birth (P=0.0235). Most of detected HHV-6 DNAs in saliva were HHV-6B. Both viral DNA loads were significantly lower (HHV-6:P=0.0101, HHV-7:P=0.0044) in the subjects with abnormal EPDS scores.

CONCLUSIONS

Detection rate and viral DNA load of both viruses in saliva increased after the third trimester. Salivary virus DNA shedding was significantly lower in subjects with an abnormal EPDS score. This article is protected by copyright. All rights reserved.

The Impact of Age and Gender and Their Association with Chemosensory Dysfunction, in Hospitalized and Self-Quarantine Patients with Covid-19 Infection, in Epirus, Greece

Objective:Olfactory and gustatory dysfunction that relates with the infection from severe acute respiratory syndrome-related coronavirus (SARS-CoV-2) has already improved. The relation between chemosensory dysfunction and age and gender in covid-19 positive patients is the main objective of the present study. Methods:We used a questionnaire to select information about medical history, patient demographics and reported symptoms during infection. Three hundred covid-19 positive patients, who underwent a RT-PCR test in the University Hospital of Ioannina, Grecce, were included in this study; 150 of them recovered at home and the remaining 150 were admitted to hospital. Statistical analysis based on ÉBM-SPSS Statistics 26.0 was done. Results:The total sample included 300 patients, of which 106 females and 194 males. There was a statistically significant difference between the subgroup of patients aged 21-25, 61-65 and 71-75 with loss of smell, that of hospitalized patients aged 41-45 with loss of smell and the subgroup of those aged 31-35 and 71-75 with loss of taste. Conclusion:There is a significant association between chemosensory dysfunction and younger age groups. Olfactory and gustatory dysfunction appears more frequently in women than men. Male gender relates with disease severity.

Herpesvirus Infections in KIR2DL2-Positive Multiple Sclerosis Patients: Mechanisms Triggering Autoimmunity

In multiple sclerosis (MS), there is a possible relationship with viral infection, evidenced by clinical evidence of an implication of infectious events with disease onset and/or relapse. The aim of this research is to study how human herpesvirus (HHVs) infections might dysregulate the innate immune system and impact autoimmune responses in MS. We analyzed 100 MS relapsing remitting patients, in the remission phase, 100 healthy controls and 100 subjects with other inflammatory neurological diseases (OIND) (neuro-lupus) for their immune response to HHV infection. We evaluated NK cell response, levels of HHVs DNA, IgG and pro- and anti-inflammatory cytokines. The results demonstrated that the presence of KIR2DL2 expression on NK cells increased the susceptibility of MS patients to HHV infections. We showed an increased susceptibility mainly to EBV and HHV-6 infections in MS patients carrying the KIR2DL2 receptor and HLA-C1 ligand. The highest HHV-6 viral load was observed in MS patients, with an increased percentage of subjects positive for IgG against HHV-6 in KIR2DL2-positive MS and OIND subjects compared to controls. MS and OIND patients showed the highest levels of IL-8, IL-12p70, IL-10 and TNF-alpha in comparison with control subjects. Interestingly, MS and OIND patients showed similar levels of IL-8, while MS patients presented higher IL-12p70, TNF-alpha and IL-10 levels in comparison with OIND patients. We can hypothesize that HHVs’ reactivation, by inducing immune activation via also molecular mimicry, may have the ability to induce autoimmunity and cause tissue damage and consequent MS lesion development.

Smell deficits in COVID-19 and possible links with Parkinson's disease

Olfactory impairment is a common symptom in Coronavirus Disease 2019 (COVID-19), the disease caused by Severe Acute Respiratory Syndrome—Coronavirus 2 (SARS-CoV-2) infection. While other viruses, such as influenza viruses, may affect the ability to smell, loss of olfactory function is often smoother and associated to various degrees of nasal symptoms. In COVID-19, smell loss may appear also in absence of other symptoms, frequently with a sudden onset. However, despite great clinical interest in COVID-19 olfactory alterations, very little is known concerning the mechanisms underlying these phenomena. Moreover, olfactory dysfunction is observed in neurological conditions like Parkinson's disease (PD) and can precede motor onset by many years, suggesting that viral infections, like COVID-19, and regional inflammatory responses may trigger defective protein aggregation and subsequent neurodegeneration, potentially linking COVID-19 olfactory impairment to neurodegeneration. In the following chapter, we report the neurobiological and neuropathological underpinnings of olfactory impairments encountered in COVID-19 and discuss the implications of these findings in the context of neurodegenerative disorders, with particular regard to PD and alpha-synuclein pathology.

Human herpesvirus 6A U4 inhibits proteasomal degradation of amyloid precursor protein

Human herpesvirus 6 (HHV-6) belongs to the betaherpesvirus subfamily and is divided into two distinct species, HHV-6A and HHV-6B. HHV-6 can infect nerve cells and is associated with a variety of nervous system diseases. Recently, the association of HHV-6A infection with Alzheimer's disease (AD) has been suggested. The main pathological phenomena of AD are the accumulation of β-amyloid (Aβ), neurofibrillary tangles, and neuroinflammation, however, the specific molecular mechanism of pathogenesis of AD is not fully clear. In this study, we focused on the effect of HHV-6A U4 gene function on Aβ expression. Co-expression of HHV-6A U4 with APP resulted in inhibition of ubiquitin-mediated proteasomal degradation of amyloid precursor protein (APP). Consequently, accumulation of β-amyloid peptide (Aβ), insoluble neurofibrillary tangles, and loss of neural cells may occur. Immunoprecipitation coupled to mass spectrometry (IP-MS) showed that HHV-6A U4 protein interacts with E3 ubiquitin ligase composed of DDB1 and Cullin 4B which is also responsible for APP degradation. We hypothesize that HHV-6A U4 protein competes with APP for binding to E3 ubiquitin ligase, resulting in inhibition of APP ubiquitin modification and clearance. Finally, this is leading to the increase of APP expression and Aβ deposition, which is the hallmark of AD. These findings provide novel evidence for the etiological hypothesis of AD that can contribute to the further analysis of HHV-6A role in AD. IMPORTANCE The association of HHV-6A infection with Alzheimer's disease has attracted increasing attention, although its role and molecular mechanism remain to be established. Our results here indicate that HHV-6A U4 inhibits APP (amyloid precursor protein) degradation. U4 protein interacts with CRLs (Cullin-RING E3 ubiquitin-protein ligases) which is also responsible for APP degradation. We propose a model that U4 competitively binds to CRLs with APP, resulting in APP accumulation and Aβ generation. Our findings provide new insights into the etiological hypothesis of HHV-6A in AD that can help further analyses.

Cumulative Roles for Epstein-Barr Virus, Human Endogenous Retroviruses, and Human Herpes Virus-6 in Driving an Inflammatory Cascade Underlying MS Pathogenesis

Roles for viral infections and aberrant immune responses in driving localized neuroinflammation and neurodegeneration in multiple sclerosis (MS) are the focus of intense research. Epstein-Barr virus (EBV), as a persistent and frequently reactivating virus with major immunogenic influences and a near 100% epidemiological association with MS, is considered to play a leading role in MS pathogenesis, triggering localized inflammation near or within the central nervous system (CNS). This triggering may occur directly via viral products (RNA and protein) and/or indirectly via antigenic mimicry involving B-cells, T-cells and cytokine-activated astrocytes and microglia cells damaging the myelin sheath of neurons. The genetic MS-risk factor HLA-DR2b (DRB1*1501β, DRA1*0101α) may contribute to aberrant EBV antigen-presentation and anti-EBV reactivity but also to mimicry-induced autoimmune responses characteristic of MS. A central role is proposed for inflammatory EBER1, EBV-miRNA and LMP1 containing exosomes secreted by viable reactivating EBV+ B-cells and repetitive release of EBNA1-DNA complexes from apoptotic EBV+ B-cells, forming reactive immune complexes with EBNA1-IgG and complement. This may be accompanied by cytokine- or EBV-induced expression of human endogenous retrovirus-W/-K (HERV-W/-K) elements and possibly by activation of human herpesvirus-6A (HHV-6A) in early-stage CNS lesions, each contributing to an inflammatory cascade causing the relapsing-remitting neuro-inflammatory and/or progressive features characteristic of MS. Elimination of EBV-carrying B-cells by antibody- and EBV-specific T-cell therapy may hold the promise of reducing EBV activity in the CNS, thereby limiting CNS inflammation, MS symptoms and possibly reversing disease. Other approaches targeting HHV-6 and HERV-W and limiting inflammatory kinase-signaling to treat MS are also being tested with promising results. This article presents an overview of the evidence that EBV, HHV-6, and HERV-W may have a pathogenic role in initiating and promoting MS and possible approaches to mitigate development of the disease.

A Review on SARS-CoV-2-Induced Neuroinflammation, Neurodevelopmental Complications, and Recent Updates on the Vaccine Development

Coronavirus disease 2019 (COVID-19) is a devastating viral infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The incidence and mortality of COVID-19 patients have been increasing at an alarming rate. The mortality is much higher in older individuals, especially the ones suffering from respiratory distress, cardiac abnormalities, renal diseases, diabetes, and hypertension. Existing evidence demonstrated that SARS-CoV-2 makes its entry into human cells through angiotensin-converting enzyme 2 (ACE-2) followed by the uptake of virions through cathepsin L or transmembrane protease serine 2 (TMPRSS2). SARS-CoV-2-mediated abnormalities in particular cardiovascular and neurological ones and the damaged coagulation systems require extensive research to develop better therapeutic modalities. As SARS-CoV-2 uses its S-protein to enter into the host cells of several organs, the S-protein of the virus is considered as the ideal target to develop a potential vaccine. In this review, we have attempted to highlight the landmark discoveries that lead to the development of various vaccines that are currently under different stages of clinical progression. Besides, a brief account of various drug candidates that are being tested to mitigate the burden of COVID-19 was also covered. Further, in a dedicated section, the impact of SARS-CoV-2 infection on neuronal inflammation and neuronal disorders was discussed. In summary, it is expected that the content covered in this article help to understand the pathophysiology of COVID-19 and the impact on neuronal complications induced by SARS-CoV-2 infection while providing an update on the vaccine development.

Effect of Lactococcus lactis Strain Plasma on HHV-6 and HHV-7 Shedding in Saliva: A Prospective Observational Study

HHV-6 and HHV-7 can reactivate in the salivary gland in response to various host stresses. Lactococcus lactis strain Plasma (LC-Plasma) can activate plasmacytoid dendritic cells (pDCs) and decrease viral infection. We investigated whether LC-Plasma intake could decrease HHV-6 and HHV-7 reactivation in the salivary gland. A total of 54 healthy volunteers were enrolled in this study. Participants took LC-Plasma granules daily for 6 weeks. Saliva samples were collected from subjects weekly for 4 weeks before (first), during (second), and after (third period) LC-Plasma intake. There was a 2-week interval between the first and second periods and a 3-week interval between the second and third periods. Mean salivary HHV-6 and HHV-7 DNA loads were compared among the three observation periods. In the first period (baseline data of viral DNA shedding), HHV-6 DNA shedding was significantly higher in subjects under 40 years old, and HHV-7 DNA shedding was significantly higher in males. HHV-6 and HHV-7 DNA loads did not significantly differ between periods. Meanwhile, in a subgroup analysis of the subjects under 40 years old, HHV-6 DNA load was significantly lower in the second period than in the first period. LC-Plasma decreases HHV-6 reactivation in the salivary glands in younger adults.

The unfolding palette of COVID-19 multisystemic syndrome and its neurological manifestations

Although our current knowledge of the pathophysiology of COVID-19 is still fragmentary, the information so far accrued on the tropism and life cycle of its etiological agent SARS-CoV-2, together with the emerging clinical data, suffice to indicate that the severe acute pulmonary syndrome is the main, but not the only manifestation of COVID-19. Necropsy studies are increasingly revealing underlying endothelial vasculopathies in the form of micro-haemorrhages and micro-thrombi. Intertwined with defective antiviral responses, dysregulated coagulation mechanisms, abnormal hyper-inflammatory reactions and responses, COVID-19 is disclosing a wide pathophysiological palette. An additional property in categorising the disease is the combination of tissue (e.g. neuro- and vasculo-tropism) with organ tropism, whereby the virus preferentially attacks certain organs with highly developed capillary beds, such as the lungs, gastrointestinal tract, kidney and brain. These multiple clinical presentations confirm that the acute respiratory syndrome as described initially is increasingly unfolding as a more complex nosological entity, a multiorgan syndrome of systemic breadth. The neurological manifestations of COVID-19, the focus of this review, reflect this manifold nature of the disease.

The impact of SARS-Cov-2 on the Nervous system and Mental Health

The World Health Organization declared the pandemic situation caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus-2) in March 2020, but the detailed pathophysiological mechanisms of Coronavirus disease 2019 (COVID-19) are not yet completely understood. Therefore, to date, few therapeutic options are available for patients with mild-moderate or serious disease. In addition to systemic and respiratory symptoms, several reports have documented various neurological symptoms and impairments of mental health. The current review aims to provide the available evidence about the effects of SARS-CoV-2 infection on mental health. The present data suggest that SARS-CoV-2 produces a wide range of impairments and disorders of the brain. However, a limited number of studies investigated the neuroinvasive potential of SARS-CoV-2. Although the main features and outcomes of COVID-19 are linked to severe acute respiratory illness, the possible damages on the brain should be considered, too.

Temporal lobe epilepsy associated with human herpes virus 6

Human herpes virus 6 (HHV-6) is a ubiquitous and most common pathogen that affects humans. Human herpes virus 6B (HHV-6B) is a wide spread human herpesvirus that infects most people when they are children, establishes latent infections in the central nervous system (CNS), especially in the hippocampus and amygdala, and induces neurologic diseases. HHV-6 can establish a latent infection and be reactivated by various stimuli. Recently, viral genomic DNA of HHV-6B has been detected in surgically removed brain tissues of intractable epilepsy patients, suggesting the involvement of HHV-6B in the pathogenesis of epilepsy. Temporal lobe epilepsy (TLE) has been shown to be closely related with HHV-6B. TLE patients with HHV-6B in their brains suffer from reiterative attacks of febrile seizures and hippocampal sclerosis. However, the mechanisms underlying the contribution of this virus to the development of TLE remains unknown. The direct damage and immune activation caused by the virus are involved in the process of neuron damage, abnormal neural circuit formation and glial cell proliferation. In addition, some cytokines like interleukin-17A (IL-17A), nuclear factor-kappa B (NF-κb), transforming growth factor-β (TGF-β), mitogen-activated protein kinase (MAPK) and phospholipase A2 are up-regulated and involved in the pathological process of TLE. More studies are needed to clarify the mechanisms underlying the link between HHV-6B and epilepsy, and identify biomarkers to recognize different patient groups for anti-inflammatory or immunomodulatory therapies.

Mechanisms of viral persistence in the brain and therapeutic approaches

There is growing recognition of the diversity of viruses that can infect the cells of the central nervous system (CNS). While the majority of CNS infections are successfully cleared by the immune response, some viral infections persist in the CNS. As opposed to resolved infections, persistent viruses can contribute to ongoing tissue damage and neuroinflammatory processes. In this manuscript, we provide an overview of the current understanding of factors that lead to viral persistence in the CNS including how viruses enter the brain, how these pathogens evade antiviral immune system responses, and how viruses survive and transmit within the CNS. Further, as the CNS may serve as a unique viral reservoir, we examine the ways in which persistent viruses in the CNS are being targeted therapeutically.

Human Herpesviruses 6A and 6B in Reproductive Diseases

Human herpesviruses 6A (HHV-6A) and human herpesvirus 6B (HHV-6B)—collectively, HHV-6A/B—are recently-discovered but ancient human viruses. The vast majority of people acquire one or both viruses, typically very early in life, producing an ineradicable lifelong infection. The viruses have been linked to several neurological, pulmonary and hematological diseases. In early human history, the viruses on multiple occasions infected a germ cell, and integrated their DNA into a human chromosome. As a result, about 1% of humans are born with the full viral genome present in every cell, with uncertain consequences for health. HHV-6A may play a role in 43% of cases of primary unexplained infertility. Both the inherited and acquired viruses may occasionally trigger several of the factors that are important in the pathogenesis of preeclampsia. Transplacental infection occurs in 1-2% of pregnancies, with some evidence suggesting adverse health consequences for the child. While emerging knowledge about these viruses in reproductive diseases is not sufficient to suggest any changes in current practice, we write this review to indicate the need for further research that could prove practice-changing.

Chemosensory Systems in COVID-19: Evolution of Scientific Research

COVID-19 disease induced by coronavirus SARS-CoV-2 presents among its symptoms alterations of the chemosensory functions. In the first studies on the Chinese population, this symptomatology was not particularly relevant, and hyposmia and hypogeusia were excluded from the symptoms to be evaluated to diagnose the disease. With the pandemic spread of the illness, there has been an augment in reports on chemosensory dysfunctions among patients. The first data analysis showed the presence of these disorders mainly in paucisymptomatic and asymptomatic patients. The interest in chemosensory systems therefore increased considerably, because the olfactory and gustatory symptoms could be the key to stop the infection spread. Furthermore, the degree of alert and attention grew, considering that these types of dysfunctions are prognostic symptoms of serious neurodegenerative diseases. About 9 months have passed since the first anecdotal reports on the involvement of the olfactory and gustatory systems in the COVID-19 pathology. For this reason, a careful review of the literature was conducted to understand if it is clearer which people present chemosensory symptoms and if these are related to the severity of the disease. Furthermore, we have identified which aspects still remain to be clarified.

Development of Rift valley fever encephalitis in rats is mediated by early infection of olfactory epithelium and neuroinvasion across the cribriform plate

The zoonotic emerging Rift Valley fever virus (RVFV) causes sporadic disease in livestock and humans throughout Africa and the Saudi Arabian peninsula. Infection of people with RVFV can occur through mosquito bite or mucosal exposure during butchering or milking of infected livestock. Disease typically presents as a self-limiting fever; however, in rare cases, hepatitis, encephalitis and ocular disease may occur. Recent studies have illuminated the neuropathogenic mechanisms of RVFV in a rat aerosol infection model. Neurological disease in rats is characterized by breakdown of the blood-brain barrier late in infection, infiltration of leukocytes to the central nervous system (CNS) and massive viral replication in the brain. However, the route of RVFV entry into the CNS after inhalational exposure remains unknown. Here, we visualized the entire nasal olfactory route from snout to brain after RVFV infection using RNA in situ hybridization and immunofluorescence microscopy. We found widespread RVFV-infected cells within the olfactory epithelium, across the cribriform plate, and in the glomerular region of the olfactory bulb within 2 days of infection. These results indicate that the olfactory tract is a major route of infection of the brain after inhalational exposure. A better understanding of potential neuroinvasion pathways can support the design of more effective therapeutic regiments for the treatment of neurological disease caused by RVFV.

Viral infections and their relationship to neurological disorders

The chronic dysfunction of neuronal cells, both central and peripheral, a characteristic of neurological disorders, may be caused by irreversible damage and cell death. In 2016, more than 276 million cases of neurological disorders were reported worldwide. Moreover, neurological disorders are the second leading cause of death. Generally, the etiology of neurological diseases is not fully understood. Recent studies have related the onset of neurological disorders to viral infections, which may cause neurological symptoms or lead to immune responses that trigger these pathological signs. Currently, this relationship is mostly based on epidemiological data on infections and seroprevalence of patients who present with neurological disorders. The number of studies aiming to elucidate the mechanism of action by which viral infections may directly or indirectly contribute to the development of neurological disorders has been increasing over the years but these studies are still scarce. Comprehending the pathogenesis of these diseases and exploring novel theories may favor the development of new strategies for diagnosis and therapy in the future. Therefore, the objective of the present study was to review the main pieces of evidence for the relationship between viral infection and neurological disorders such as Alzheimer's disease, Parkinson's disease, Guillain-Barré syndrome, multiple sclerosis, and epilepsy. Viruses belonging to the families Herpesviridae, Orthomyxoviridae, Flaviviridae, and Retroviridae have been reported to be involved in one or more of these conditions. Also, neurological symptoms and the future impact of infection with SARS-CoV-2, a member of the family Coronaviridae that is responsible for the COVID-19 pandemic that started in late 2019, are reported and discussed.

Does coronaviruses induce neurodegenerative diseases? A systematic review on the neurotropism and neuroinvasion of SARS-CoV-2

The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified in 2019 in Wuhan, China. Clinically, respiratory tract symptoms as well as other organs disorders are observed in patients positively diagnosed coronavirus disease 2019 (COVID-19). In addition, neurological symptoms, mainly anosmia, ageusia and headache were observed in many patients. Once in the central nervous system (CNS), the SARS-CoV-2 can reside either in a quiescent latent state, or eventually in actively state leading to severe acute encephalitis, characterized by neuroinflammation and prolonged neuroimmune activation. SRAS-CoV-2 requires angiotensin-converting enzyme 2 (ACE2) as a cell entry receptor. The expression of this receptor in endothelial cells of blood-brain barrier (BBB) shows that SRAS-CoV-2 may have higher neuroinvasive potential compared to known coronaviruses. This review summarizes available information regarding the impact of SRAS-CoV-2 in the brain and tended to identify its potential pathways of neuroinvasion. We offer also an understanding of the long-term impact of latently form of SARS-CoV-2 on the development of neurodegenerative disorders. As a conclusion, the persistent infection of SRAS-CoV-2 in the brain could be involved on human neurodegenerative diseases that evolve a gradual process, perhapes, over several decades.

Limbic Encephalitis Brain Damage Induced by Cocal Virus in Adult Mice Is Reduced by Environmental Enrichment: Neuropathological and Behavioral Studies

We previously demonstrated, using the Piry virus model, that environmental enrichment promotes higher T-cell infiltration, fewer microglial changes, and faster central nervous system (CNS) virus clearance in adult mice. However, little is known about disease progression, behavioral changes, CNS cytokine concentration, and neuropathology in limbic encephalitis in experimental models. Using Cocal virus, we infected C57Bl6 adult mice and studied the neuroanatomical distribution of viral antigens in correlation with the microglial morphological response, measured the CNS cytokine concentration, and assessed behavioral changes. C57Bl6 adult mice were maintained in an impoverished environment (IE) or enriched environment (EE) for four months and then subjected to the open field test. Afterwards, an equal volume of normal or virus-infected brain homogenate was nasally instilled. The brains were processed to detect viral antigens and microglial morphological changes using selective immunolabeling. We demonstrated earlier significant weight loss and higher mortality in IE mice. Additionally, behavioral analysis revealed a significant influence of the environment on locomotor and exploratory activity that was associated with less neuroinvasion and a reduced microglial response. Thus, environmental enrichment was associated with a more effective immune response in a mouse model of limbic encephalitis, allowing faster viral clearance/decreased viral dissemination, reduced disease progression, and less CNS damage.

Human Herpesviruses 6A and 6B in Brain Diseases: Association versus Causation

Human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B), collectively termed HHV-6A/B, are neurotropic viruses that permanently infect most humans from an early age. Although most people infected with these viruses appear to suffer no ill effects, the viruses are a well-established cause of encephalitis in immunocompromised patients. In this review, we summarize the evidence that the viruses may also be one trigger for febrile seizures (including febrile status epilepticus) in immunocompetent infants and children, mesial temporal lobe epilepsy, multiple sclerosis (MS), and, possibly, Alzheimer's disease. We propose criteria for linking ubiquitous infectious agents capable of producing lifelong infection to any neurologic disease, and then we examine to what extent these criteria have been met for these viruses and these diseases.

Kinetics and clinical significance of human herpesvirus 6 DNA shedding in saliva after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Little is known about the kinetics and clinical significance of saliva human herpesvirus-6 (HHV-6) DNA after hematopoietic stem cell transplantation (HSCT).

METHODS

In this observational study, we quantified HHV-6 DNA in serially collected plasma and saliva from allogeneic HSCT recipients. Associations between the status of salivary HHV-6 DNA and the development of HHV-6 encephalitis, depression, and oral mucosal graft-versus-host disease (GVHD) were retrospectively analyzed.

RESULTS

A total of 787 plasma and 434 saliva samples were collected from 56 patients. The cumulative incidence of HHV-6 DNA in plasma and saliva at 60 days after transplantation was 51.8% and 83.9%, respectively. The peak level of salivary HHV-6 DNA was significantly higher in patients who displayed plasma HHV-6 DNA than in those who did not (median, 51,584 copies/mL vs 587 copies/mL; P < .0001). Salivary HHV-6 DNA levels increased after positive plasma HHV-6 DNA was detected and remained high during observation period. Despite the frequent occurrence of positive salivary HHV-6 DNA, no patient developed depression. Positivity of salivary HHV-6 DNA was not significantly associated with the development of HHV-6 encephalitis (P = 1.00, Fisher's exact test) or oral mucosal GVHD (P = .71, Grey's test). No significant relationship between salivary HHV-6 DNA and these diseases was found even when comparing higher HHV-6 DNA loads in saliva.

CONCLUSION

Salivary HHV-6 DNA levels increased after HHV-6 DNA was detected in the blood. However, no epidemiological evidence was shown to support a role of salivary HHV-6 in the development of HHV-6 encephalitis, depression, and oral mucosal GVHD.

The Presence of Human Herpesvirus 6 in the Brain in Health and Disease

The human herpesvirus 6 (HHV-6) -A and -B are two dsDNA beta-herpesviruses infectingalmost the entire worldwide population. These viruses have been implicated in multipleneurological conditions in individuals of various ages and immunological status, includingencephalitis, epilepsy, and febrile seizures. HHV-6s have also been suggested as playing a role inthe etiology of neurodegenerative diseases such as multiple sclerosis and Alzheimer's disease. Theapparent robustness of these suggested associations is contingent on the accuracy of HHV-6detection in the nervous system. The effort of more than three decades of researching HHV-6 in thebrain has yielded numerous observations, albeit using variable technical approaches in terms oftissue preservation, detection techniques, sample sizes, brain regions, and comorbidities. In thisreview, we aimed to summarize current knowledge about the entry routes and direct presence ofHHV-6 in the brain parenchyma at the level of DNA, RNA, proteins, and specific cell types, inhealthy subjects and in those with neurological conditions. We also discuss recent findings relatedto the presence of HHV-6 in the brains of patients with Alzheimer's disease in light of availableevidence.

Anosmia: a missing link in the neuroimmunology of coronavirus disease 2019 (COVID-19)

Just before 2020 began, a novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), brought for humans a potentially fatal disease known as coronavirus disease 2019 (COVID-19). The world has thoroughly been affected by COVID-19, while there has been little progress towards understanding the pathogenesis of COVID-19. Patients with a severe phenotype of disease and those who died from the disease have shown hyperinflammation and were more likely to develop neurological manifestations, linking the clinical disease with neuroimmunological features. Anosmia frequently occurs early in the course of COVID-19. The prevalence of anosmia would be influenced by self-diagnosis as well as self-misdiagnosis in patients with COVID-19. Despite this, the association between anosmia and COVID-19 has been a hope for research, aiming to understand the pathogenesis of COVID-19. Studies have suggested differently probable mechanisms for the development of anosmia in COVID-19, including olfactory cleft syndrome, postviral anosmia syndrome, cytokine storm, direct damage of olfactory sensory neurons, and impairment of the olfactory perception center in the brain. Thus, the observation of anosmia would direct us to find the pathogenesis of COVID-19 in the central nervous system, and this is consistent with numerous neurological manifestations related to COVID-19. Like other neurotropic viruses, SARS-CoV-2 might be able to enter the central nervous system via the olfactory epithelium and induce innate immune responses at the site of entry. Viral replication in the nonneural olfactory cells indirectly causes damage to the olfactory receptor nerves, and as a consequence, anosmia occurs. Further studies are required to investigate the neuroimmunology of COVID-19 in relation to anosmia.

COVID-19 and seizures: Is there a link?

The rapid spread of the SARS‐CoV‐2 pandemic poses particular challenges to the management of persons with chronic disease. Reports of a possible neuroinvasiveness of SARS‐CoV‐2 as well as pathophysiological mechanisms and indirect consequences in severe COVID‐19 cases raise the question of whether the infection can be associated with an increased risk of seizure recurrence or the development of new onset and acute symptomatic seizures. Although the literature does not provide relevant evidence for seizure worsening in persons with epilepsy during the course of a SARS‐CoV‐2 infection, there are theoretical risks, for example, seizures triggered by fever. Moreover, a severe disease course and advanced disease stages can, for instance, result in hypoxic encephalopathy, cerebrovascular events, and cytokine storm, which may trigger the development of acute seizures. This is further confirmed by reports of occasional seizures in COVID‐19 patients. Although the low number of reports so far suggests that the risk may be relatively low, the reports indicate that an early neurological manifestation with seizures should not be ruled out. In the context of these cases, we discuss possible pathophysiological mechanisms that may trigger ictogenesis in patients with SARS‐CoV‐2 infection.

Update on neurological manifestations of COVID-19

Novel coronavirus (severe acute respiratory syndrome coronavirus-2: SARS-CoV-2) has a high homology with other cousin of coronaviruses such as SARS and Middle East respiratory syndrome-related coronavirus (MERS). After outbreak of the SARS-CoV-2 in China, it has spread so fast around the world. The main complication of coronavirus disease 2019 (COVID-19) is respiratory failure, but several patients have also been admitted to the hospital with neurological symptoms. Direct invasion, hematogenic rout, retrograde and anterograde transport along peripheral nerves are considered as main neuroinvasion mechanisms of SARS-CoV-2. In the present study, we describe the possible routes for entering of SARS-CoV-2 into the nervous system. Then, the neurological manifestations of the SARS-CoV-2 infection in the central nervous system (CNS) and peripheral nervous system (PNS) are reviewed. Furthermore, the neuropathology of the virus and its impacts on other neurological disorders are discussed.

Effects of Antimalarial Drugs on Neuroinflammation-Potential Use for Treatment of COVID-19-Related Neurologic Complications

The SARS-CoV-2 virus that is the cause of coronavirus disease 2019 (COVID-19) affects not only peripheral organs such as the lungs and blood vessels, but also the central nervous system (CNS)—as seen by effects on smell, taste, seizures, stroke, neuropathological findings and possibly, loss of control of respiration resulting in silent hypoxemia. COVID-19 induces an inflammatory response and, in severe cases, a cytokine storm that can damage the CNS. Antimalarials have unique properties that distinguish them from other anti-inflammatory drugs. (A) They are very lipophilic, which enhances their ability to cross the blood-brain barrier (BBB). Hence, they have the potential to act not only in the periphery but also in the CNS, and could be a useful addition to our limited armamentarium against the SARS-CoV-2 virus. (B) They are non-selective inhibitors of phospholipase A₂ isoforms, including cytosolic phospholipase A₂ (cPLA₂). The latter is not only activated by cytokines but itself generates arachidonic acid, which is metabolized by cyclooxygenase (COX) to pro-inflammatory eicosanoids. Free radicals are produced in this process, which can lead to oxidative damage to the CNS. There are at least 4 ways that antimalarials could be useful in combating COVID-19. (1) They inhibit PLA_2. (2) They are basic molecules capable of affecting the pH of lysosomes and inhibiting the activity of lysosomal enzymes. (3) They may affect the expression and Fe²⁺/H⁺ symporter activity of iron transporters such as divalent metal transporter 1 (DMT1), hence reducing iron accumulation in tissues and iron-catalysed free radical formation. (4) They could affect viral replication. The latter may be related to their effect on inhibition of PLA₂ isoforms. Inhibition of cPLA₂ impairs an early step of coronavirus replication in cell culture. In addition, a secretory PLA₂ (sPLA₂) isoform, PLA2G2D, has been shown to be essential for the lethality of SARS-CoV in mice. It is important to take note of what ongoing clinical trials on chloroquine and hydroxychloroquine can eventually tell us about the use of antimalarials and other anti-inflammatory agents, not only for the treatment of COVID-19, but also for neurovascular disorders such as stroke and vascular dementia.

HHV-6 and hippocampal volume in patients with mesial temporal sclerosis

Objective

To study the effects of human herpes virus 6 (HHV‐6) on the hippocampal volume in patients with mesial temporal sclerosis (MTS).

Background

HHV‐6 may play an etiologic role in MTS. Previous studies found a possible association with febrile status epilepticus. Several investigators have reported a higher prevalence of HHV‐6 in MTS resections compared to other epilepsy etiologies.

Design/Methods

We used FreeSurfer to segment cortical structures and obtain whole hippocampal and subfield volumes in 41 patients with intractable epilepsy. In addition, an investigator blinded to other data traced hippocampi manually on each slice. The main study outcome measure was the asymmetry index (AI) between hippocampal volumes ipsilateral and contralateral to seizure foci compared between HHV‐6 positive and negative patients. Viral DNA was isolated from fresh brain tissue obtained at temporal lobectomy. For 25 patients, viral detection was performed using quantitative real‐time PCR specific for HHV‐6A and HHV‐6B. For 16 patients, viral DNA detection was performed using digital droplet PCR specific for HHV‐6A and HHV‐6B.

Results

Twenty‐two patients were positive (14 of 25 tested with real‐time PCR, and 8 of 16 with digital droplet PCR), and 19 negatives for HHV‐6. HHV‐6 negative patients had significantly greater AI and lower total hippocampal volume ipsilateral to seizure foci than HHV‐6 positive patients. Epilepsy duration and age of onset did not affect results.

Interpretation

Our data suggest multiple potential etiologies for MTS. HHV‐6 may have a less severe effect on the hippocampus than other etiologies.

The role of human herpesvirus-6 and inflammatory markers in the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a destructive autoimmune neuroinflammatory and neurodegenerative disorder of the central nervous system (CNS) with unknown etiology and mechanism of pathogenesis. Pathogens, especially human herpes viruses, have been suggested as environmental factors of the MS and other neuroinflammatory disorders. This study aimed to determine the prevalence of HHV-6 antibody response in MS patients and investigate the levels of pro/anti-inflammatory cytokine and chemokines in MS patients in comparison with healthy subjects. Two hundred sixty-three patients with clinically defined MS (140 females and 123 males), along with 263 healthy subjects (140 females and 123 males), were recruited for this study. After the analysis of HHV-6 seropositivity/seronegativity, the levels of some pro/anti-inflammatory cytokines, including TNF-α, IFN-γ, IL-1β, IL-6, and IL-12 as well as two chemokines, namely CCL-2 and CCL-5 were determined by the enzyme-linked immunosorbent assay (ELISA) method in HHV-6 seropositive/seronegative MS patients and healthy subjects. Our results showed that the serum concentrations of TNF-α, IFN-γ, IL-1β, IL-6, and CCL-5 elevated in HHV-6 seropositive compared with seronegative MS patients (P < .05). Moreover, the levels of IL-12, IL-10, and CCL-2 levels were significantly lower in seropositive MS patients when compared with seronegative MS patients (P < .05). Also, our results revealed that the mean values of the expanded disability status scale (EDSS) were significantly higher in HHV-6 seropositive versus seronegative MS patients (P < .05). In conclusion, we proposed that HHV-6 infection may play a role in MS pathogenesis by changing cytokine signaling in MS patients that may lead to peripheral inflammation.

Human Herpesvirus 6B Greatly Increases Risk of Depression by Activating Hypothalamic-Pituitary -Adrenal Axis during Latent Phase of Infection

Little is known about the effect of latent-phase herpesviruses on their host. Human herpesvirus 6B (HHV-6B) is one of the most ubiquitous herpesviruses, and olfactory astrocytes are one of the most important sites of its latency. Here, we identified SITH-1, an HHV-6B latent protein specifically expressed in astrocytes. Mice induced to produce SITH-1 in their olfactory astrocytes exhibited olfactory bulb apoptosis, a hyper-activated hypothalamic-pituitary-adrenal (HPA) axis and depressive symptoms. The binding of SITH-1 to the host protein calcium-modulating ligand (CAML) to form an activated complex promoted the influx of extracellular calcium. The serum antibody titers for depressive patients with respect to this activated complex were significantly higher than for normal controls (p = 1.78 × 10⁻¹⁵), when the antibody positive rates were 79.8% and 24.4%, respectively, and the odds ratio was 12.2. These results suggest that, in the latent phase, HHV-6B may be involved in the onset of depression.

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We identified SITH-1, a new protein specific to HHV-6B latent infection

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Mice expressing SITH-1 at HHV-6B latent infection site had depressive symptoms

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Depressive symptoms due to SITH-1 were associated with a hyper-activated HPA axis

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SITH-1-specific antibody detection significantly greater in depressive patients

Persistent Roseoloviruses Infection in Adult Patients with Epilepsy

Background: Human herpesviruses (HHV)-6A, HHV-6B and HHV-7 are considered to be involved in the pathogenesis of epilepsy, a common neurological disorder. The objective of this study was to determine the association of roseoloviruses infection with epilepsy. Methods: 53 epilepsy patients and 104 ordinary blood donors were analyzed to determine presence of virus-specific antibodies by enzyme-linked immunosorbent assay (ELISA) and immunofluorescence assay (IFA), genomic sequences, viral load and gene expression by polymerase chain reactions (PCRs) and restriction analysis, HHV-6 protein expression by IFA and level of cytokines by ELISA. Results: Roseoloviruses genomic sequences in DNA samples from whole blood were found in 86.8% of patients versus 54.8% of controls and active infection was revealed only in patients with epilepsy (19.6% of roseolovirus-positive patients). Significantly higher viral load and more frequent gene expression was detected in patients compared to the controls. HHV-6-encoded protein expression was demonstrated in 53.3% of patients with previously detected HHV-6 DNA. Changes in level of cytokines were determined in patients with elevated viral load compared to the patients without elevated viral loads and to the controls. Conclusions: Results on frequent active HHV-6 and HHV-7 infection in epilepsy patient’ peripheral blood indicate on possible involvement of these viruses in the disease development.

SARS-CoV-2: Olfaction, Brain Infection, and the Urgent Need for Clinical Samples Allowing Earlier Virus Detection

The novel SARS-CoV-2 virus has very high infectivity, which allows it to spread rapidly around the world. Attempts at slowing the pandemic at this stage depend on the number and quality of diagnostic tests performed. We propose that the olfactory epithelium from the nasal cavity may be a more appropriate tissue for detection of SARS-CoV-2 virus at the earliest stages, prior to onset of symptoms or even in asymptomatic people, as compared to commonly used sputum or nasopharyngeal swabs. Here we emphasize that the nasal cavity olfactory epithelium is the likely site of enhanced binding of SARS-CoV-2. Multiple non-neuronal cell types present in the olfactory epithelium express two host receptors, ACE2 and TMPRSS2 proteases, that facilitate SARS-CoV-2 binding, replication, and accumulation. This may be the underlying mechanism for the recently reported cases of smell dysfunction in patients with COVID-19. Moreover, the possibility of subsequent brain infection should be considered which begins in olfactory neurons. In addition, we discuss the possibility that olfactory receptor neurons may initiate rapid immune responses at early stages of the disease. We emphasize the need to undertake research focused on additional aspects of SARS-CoV-2 actions in the nervous system, especially in the olfactory pathway.

Evolutionary analysis of exogenous and integrated HHV-6A/HHV-6B populations

Human betaherpesviruses 6A and 6B (HHV-6A and HHV-6B) are highly prevalent in human populations. The genomes of these viruses can be stably integrated at the telomeres of human chromosomes and be vertically transmitted (inherited chromosomally integrated HHV-6A/HHV-6B, iciHHV-6A/iciHHV-6B). We reconstructed the population structures of HHV-6A and HHV-6B, showing that HHV-6A diverged less than HHV-6B genomes from the projected common ancestral population. Thus, HHV-6B genomes experienced stronger drift, as also supported by calculation of nucleotide diversity and Tajima's D. Analysis of ancestry proportions indicated that HHV-6A exogenous viruses and iciHHV-6A derived most of their genomes from distinct ancestral sources. Conversely, ancestry proportions were similar in exogenous HHV-6B viruses and iciHHV-6B. In line with previous indications, this suggests the distinct exogenous viral populations that originated iciHHV-6B in subjects with European and Asian ancestry are still causing infections in the corresponding geographic areas. Notably, for both iciHHV-6A and iciHHV-6B, we found that European and American sequences tend to have high proportions of ancestry from viral populations that experienced considerable drift, suggesting that they underwent one or more bottlenecks followed by population expansion. Finally, analysis of HHV-6B exogenous viruses sampled in Japan indicated that proportions of ancestry components of most of these viruses are different from the majority of those sampled in the USA. More generally, we show that, in both viral species, both integrated and exogenous viral genomes have different ancestry components, partially depending on geographic location. It would be extremely important to determine whether such differences account for the diversity of HHV-6A/HHV-6B-associated clinical symptoms and epidemiology. Also, the sequencing of additional exogenous and integrated viral genomes will be instrumental to confirm and expand our conclusions, which are based on a relatively small number of genomes, sequenced with variable quality, and with unequal sampling in terms of geographic origin.

Human Herpesvirus-6 Meningitis in a Premature Infant with Fevers: A Case and Literature Review

Human herpesvirus-6 (HHV-6) is a common virus that can cause nearly universal infection in infancy and early childhood. It typically manifests as an acute febrile illness. We describe a case of a premature infant with congenital hydrocephalus secondary to aqueductal stenosis with a ventriculoperitoneal shunt in place who developed intermittent fevers while she was admitted to the neonatal intensive care unit. She was ultimately diagnosed with acute HHV-6 meningitis. In addition to this report, we present a literature review regarding this virus’s potential modes of transmission and forms of clinical presentation in the neonatal period.

Herpes simplex virus 1 rhombencephalitis in a patient with chromosomally integrated human herpesvirus-6A

Central nervous system infection caused by Herpes simplex virus 1 remains a significant cause of morbidity and mortality in transplant patients. Additionally, the clinical implications of the recently discovered Human herpesvirus 6A are still under investigation.

Hereby, we report a clinical case of an immunosuppressed patient following kidney transplantation and with chromosomally integrated human herpesvirus-6A (CIHHV-6A) that developed rhombencephalitis due to herpes virus simplex 1.

This case highlights the importance of investigating the CIHHV-6 status in the differential diagnosis whenever a human herpesvirus is detected in the cerebrospinal fluid.

Association of infections with multiple sclerosis in Gulf Cooperation Council countries: a review

Multiple sclerosis (MS) is an autoimmune disease that affects the central nervous system, causing inflammation, demyelination, and neurodegeneration. Infection can play a role in its etiology. Herein, a review is presented of studies that have reported an association between infection and MS risk in countries of the Arabian Gulf region. Searches of the PubMed, Google Scholar, and Science Direct databases were carried out using various search terms, and relevant studies published through January 2019 on the epidemiology of MS in Gulf Cooperation Council countries identified. MS has been found to be associated with measles in Saudi Arabia and Epstein–Barr virus in Kuwait whereas no association has been identified between risk of MS and varicella-zoster virus, mumps, or human herpesvirus-6. However, few epidemiological studies on this topic have been conducted in countries of the Gulf region. Longitudinal and serological studies to establish robust evidence between infection and risk of MS are highly recommended, and a regional MS registry is needed.

HHV-6A infection dysregulates autophagy/UPR interplay increasing beta amyloid production and tau phosphorylation in astrocytoma cells as well as in primary neurons, possible molecular mechanisms linking viral infection to Alzheimer's disease

HHV-6A and HHV-6B are neurotropic viruses able to dysregulate autophagy and activate ER stress/UPR in several cell types. The appropriate functioning of these processes is required for cell homeostasis, particularly in post-mitotic cells such as neuronal cells. Interestingly, neurodegenerative diseases such as Alzheimer's disease (AD) are often accompanied by autophagy dysregulation and abnormal UPR activation. This study demonstrated for the first time that HHV-6A infection of astrocytoma cells and primary neurons reduces autophagy, increases Aβ production and activates ER stress/UPR promoting tau protein hyper-phosphorylation. Our results support previous studies suggesting that HHV-6A infection may play a role in AD and unveil the possible underlying molecular mechanisms involved.

HHV-6A infection induces amyloid-beta expression and activation of microglial cells

BACKGROUND

The control of viral infections in the brain involves the activation of microglial cells, the macrophages of the brain that are constantly surveying the central nervous system, and the production of amyloid-beta (Aβ) as an anti-microbial molecule. Recent findings suggest a possible implication of HHV-6A in AD. We evaluated the effect of HHV-6A infection on microglial cell expression Aβ and the activation status, determined by TREM2, ApoE, cytokines, and tau expression.

METHODS

We have infected microglial cells (HMC3, ATCC®CRL-3304), in monolayer and human peripheral blood monocyte-derived microglia (PBM-microglia) spheroid 3D model, with HHV-6A (strain U1102) cell-free virus inocula with 100 genome equivalents per 1 cell. We collected the cells 1, 3, 7, and 14 days post-infection (d.p.i.) and analyzed them for viral DNA and RNA, ApoE, Aβ (1-40, 1-42), tau, and phospho-tau (Threonine 181) by real-time immunofluorescence and cytokines by immunoenzymatic assay.

RESULTS

We observed a productive infection by HHV-6A. The expression of Aβ 1-42 increased from 3 d.p.i., while no significant induction was observed for Aβ 1-40. The HHV-6A infection induced the activation (TREM2, IL-1beta, ApoE) and migration of microglial cells. The secretion of tau started from 7 d.p.i., with an increasing percentage of the phosphorylated form.

CONCLUSIONS

In conclusion, microglial cells are permissive to HHV-6A infection that induces the expression of Aβ and an activation status. Meanwhile, we hypothesize a paracrine effect of HHV-6A infection that activates and induces microglia migration to the site of infection.