Presence of human herpesviruses 6, 7, and 8 DNA sequences in normal brain tissue

Molecular Characterization of Herpesviral Encephalitis in Cetaceans: Correlation with Histopathological and Immunohistochemical Findings

Simple Summary

In this study we describe the molecular and pathological characteristics of alpha- and gamma-herpesvirus infection of the central nervous system of stranded cetaceans and correlate them with viral load, immunohistochemical findings and biological data such as age, sex, and the presence of co-infections. The viruses (alpha- and gamma-herpesvirus) were detected in twelve out of 103 analysed stranded cetaceans and were associated with a wide range of histopathological lesions, as previously described for these and other species. In five out the twelve animals, lesions were severe enough (malacia, neuronal necrosis and neuronophagia) to cause death. Intranuclear inclusions bodies were present in brain tissue samples from half of the HV-positive animals, indicating that the injury was due to an infective agent belonging to a group of filterable viruses. These results are in accordance with immunohistochemical findings, as all the brain tissue samples with INIBs were immunolabeled with Anti-HSV1. Males, juveniles, and calves were predominantly infected among the analysed cetaceans and a 41.6% (5/12) incidence of co-infections in the brain was detected, with three animals co-infected with Dolphin Morbillivirus (DMV). In this study, we present, to the best of our knowledge, the first histopathological evidence of superinfection between HV and DMV pathogens in brain tissue.

Abstract

Herpesviruses are causative agents of meningitis and encephalitis in cetaceans, which are among the main leading known natural causes of death in these species. Brain samples from 103 stranded cetaceans were retrospectively screened for the presence of herpesvirus DNA in the brain. Molecular detection of Cetacean Morbillivirus was performed in HV positive brain cases. Histopathologic evaluation of brain samples included the presence or absence of the following findings (n = 7): meningitis, perivascular cuffings, microgliosis, intranuclear inclusion bodies, malacia, neuronal necrosis and neurophagic nodules, and haemorrhages. Histological evidence of the involvement of other etiological agents led to complementary analysis. We detected the presence of alpha and gamma-HVs in 12 out of 103 (11.6%) brain samples from stranded cetaceans of five different species: one bottlenose dolphin, six striped dolphins, three Atlantic spotted dolphins, one Cuvier’s beaked whale, and one common dolphin. Pathogenic factors such as viral strain, age, sex, and the presence of co-infections were analysed and correlated with the brain histopathological findings in each case. Herpesvirus was more prevalent in males, juveniles, and calves and a 41.6% incidence of co-infections in the brain was detected in our study: three with Dolphin Morbillivirus, one with Staphilococcus aureus septicaemia and one with Brucella spp.

Encephalitis, a Rare Manifestation of Human Herpesvirus 7 Infection

Human herpesvirus 7 (HHV-7) infection typically occurs in childhood and is frequently asymptomatic. Some clinical manifestations include fever and exanthem subitum. There have been rare reports of invasion of HHV-7 into the central nervous system. Here we report a case of encephalitis associated with HHV-7. A 16-year-old girl presented with headache, vomiting, disorientation, and psychomotor agitation. Glasgow Coma Scale on arrival was 9. Cerebrospinal fluid tested positive for HHV-7. Electroencephalogram showed intermittent slowing and rare sharp waves in the left frontal region. She recovered well after appropriate treatment for encephalitis.

This case added to the few existing reports of encephalitis due to HHV-7. Physicians should be aware of this rare neurological manifestation of HHV-7 for prompt management. Similar cases should be reported to further our knowledge about this virus and its role in neurological disease.

Reanalysis of Alzheimer's brain sequencing data reveals absence of purported HHV6A and HHV7

Readhead et al. recently reported in Neuron the detection and association of human herpesviruses 6A (HHV6A) and 7 (HHV7) with Alzheimer's disease by shotgun sequencing. I was skeptical of the specificity of their modified Viromescan bioinformatics method and subsequent analysis for numerous reasons. Using their supplementary data, the prevalence of variola virus, the etiological agent of the eradicated disease smallpox, can be calculated at 97.5% of their Mount Sinai Brain Bank dataset. Reanalysis of Readhead et al.'s data using highly sensitive and specific alternative methods finds no HHV7 reads in their samples; HHV6A reads were found in only 2 out of their top 15 samples sorted by reported HHV6A abundance. Finally, recreation of Readhead et al.'s modified Viromescan method identifies reasons for its low specificity.

The role of herpesvirus 6A and 6B in multiple sclerosis and epilepsy

Human herpesvirus 6A (HHV‐6A) and 6B (HHV‐6B) are two closely related viruses that can infect cells of the central nervous system (CNS). The similarities between these viruses have made it difficult to separate them on serological level. The broad term HHV‐6 remains when referring to studies where the two species were not distinguished, and as such, the seroprevalence is over 90% in the adult population. HHV‐6B has been detected in up to 100% of infants with the primary infection roseola infantum, but less is known about the primary infection of HHV‐6A. Both viruses are neurotropic and have capacity to establish lifelong latency in cells of the central nervous system, with potential to reactivate and cause complications later in life. HHV‐6A infection has been associated with an increased risk of multiple sclerosis (MS), whereas HHV‐6B is indicated to be involved in pathogenesis of epilepsy. These two associations show how neurological diseases might be caused by viral infections, but as suggested here, through completely different molecular mechanisms, in an autoimmune disease, such as MS, by triggering an overreaction of the immune system and in epilepsy by hampering internal cellular functions when the immune system fails to eliminate the virus. Understanding the viral mechanisms of primary infection and reactivation and their spectrum of associated symptoms will aid our ability to diagnose, treat and prevent these severe and chronic diseases. This review explores the role of HHV‐6A and HHV‐6B specifically in MS and epilepsy, the evidence to date and the future directions of this field.

Alpha- and gammaherpesviruses in stranded striped dolphins (Stenella coeruleoalba) from Spain: first molecular detection of gammaherpesvirus infection in central nervous system of odontocetes

BACKGROUND

Herpesvirus infections in cetaceans have always been attributed to the Alphaherpesvirinae and Gammaherpesvirinae subfamilies. To date, gammaherpesviruses have not been reported in the central nervous system of odontocetes.

CASE PRESENTATION

A mass stranding of 14 striped dolphins (Stenella coeruleoalba) occurred in Cantabria (Spain) on 18th May 2019. Tissue samples were collected and tested for herpesvirus using nested polymerase chain reaction (PCR), and for cetacean morbillivirus using reverse transcription-PCR. Cetacean morbillivirus was not detected in any of the animals, while gammaherpesvirus was detected in nine male and one female dolphins. Three of these males were coinfected by alphaherpesviruses. Alphaherpesvirus sequences were detected in the cerebrum, spinal cord and tracheobronchial lymph node, while gammaherpesvirus sequences were detected in the cerebrum, cerebellum, spinal cord, pharyngeal tonsils, mesenteric lymph node, tracheobronchial lymph node, lung, skin and penile mucosa. Macroscopic and histopathological post-mortem examinations did not unveil the potential cause of the mass stranding event or any evidence of severe infectious disease in the dolphins. The only observed lesions that may be associated with herpesvirus were three cases of balanitis and one penile papilloma.

CONCLUSIONS

To the authors' knowledge, this is the first report of gammaherpesvirus infection in the central nervous system of odontocete cetaceans. This raises new questions for future studies about how gammaherpesviruses reach the central nervous system and how infection manifests clinically.

The effect of human herpesvirus 6B infection on the MAPK pathway

BACKGROUND

Human herpesvirus 6B (HHV-6B) is a neurotropic virus that has been repeatedly associated with mesial temporal lobe epilepsy (MTLE). However, the mechanism behind this suggested association is not known. Therefore, the aim of this study was to investigate what genes were affected by HHV-6B, possibly revealing HHV-6B induced disease causing mechanisms.

MATERIAL AND METHOD

First, gene expression in MTLE tissue positive for HHV-6B DNA (n = 10) and negative for HHV-6B DNA (n = 14) was compared using the Affymetrix® Human Gene 2.1 ST Array. Secondly, in vitro experiments were conducted where Molt-3 T cells were infected with HHV-6B and gene expression of MAP2K4 (MKK4) and 89 other genes in the MAPK signaling pathway was investigated using qPCR. In addition, phosphorylated MKK4 was assessed using IFA and the DNA methylation investigated with Illumina Infinium HumanMethylation450 BeadChip array.

RESULTS

MAP2K4 was one of the most differently expressed genes in the Affymetrix array, suggesting an upregulation by HHV-6B infection in MTLE tissue. No gene reached statistical significance but MAP2K4 was selected for further investigation in vitro, where it was clearly upregulated by HHV-6B infection both on gene expression and protein expression level. Further investigating expression of genes in the MAPK pathways in vitro revealed that several genes were affected by HHV-6B infection, but none of these genes displayed viral induced changes in DNA methylation.

CONCLUSIONS

As the MAPK pathways are involved in transforming different stimuli (like stress) into a cellular responses (like apoptosis or inflammation), it may not be surprising that genes in these pathways are affected by virus infection. This is the first report of HHV-6B's effect on these signaling cascades and given that both dysregulation of the MAPK pathways and an association with HHV-6B have been previously observed in epilepsy, a possible link of infection induced dysregulation of MAPK in epilepsy warrant further investigation.

Type specific Real time PCR for detection of human herpes virus 6 in schizophrenia and bipolar patients: a case control study

BACKGROUND

Schizophrenia (SC) and bipolar disorder (BD) are among the most devastating diseases worldwide. There are several lines of evidence suggesting that viruses may play significant roles in the etiology of these mental disorders. The aim of this study was the detection of HHV-6A/B in the peripheral blood mononuclear cells (PBMC) of SC and BD patients versus the healthy control (HC) subjects using a new method of type-specific Real time PCR analysis.

METHODS

A type-specific Real time PCR was performed for simultaneous detection and typing of HHV-6A/B in the PBMCs of 120 SC and BD patients and 75 HCs.

RESULTS

Only one case of HHV-6B out of 120 (0.8 %) SC and BD patients and two cases of HHV-6A (2.7 %) in 75 HCs were detected.

CONCLUSIONS

The low levels of HHV-6 detection in PBMCs, severely limited the capacity of this study to investigate the association between the presence of HHV-6 and BD or SC in this population, thus no conclusions can be drawn in this regard. Meanwhile this study introduces a Real time PCR based method for type specific detection of HHV-6A/B in clinical samples.

Presence of herpesvirus DNA in cerebrospinal fluid of patients with tick-borne encephalitis and enteroviral meningoencephalitis

Reactivation of HHVs in the CNS due to inflammation has not been well described yet. The primary aim of this study was to investigate the frequency of HHV DNA detection in the cerebrospinal fluid (CSF) of immunocompetent patients with meningoencephalitis of other than HHV origin. The secondary aim of this study was to evaluate the impact of herpesvirus co-infection on the clinical course and patient outcome. Ninety-six patients with clinically and laboratory proven tick-borne encephalitis (TBE) and 77 patients with a confirmed diagnosis of enteroviral meningitis (EVM), along with a control group of 107 patients without evidence of inflammation in the CSF were retrospectively tested by nested PCR for the presence of DNA of the neurotropic herpesviruses HSV1, HSV2, VZV, and HHV6 in the CSF. The clinical course, laboratory tests, antiviral treatment, and neurological complications in a 6-month follow-up were compared between the groups positive or negative for HHV DNA in the CSF. HHV DNA was found in the CSF of 12 (6.9%) patients (6.3% and 7.8% in the TBE and EVM groups, respectively) and in 1 (0.9%) control patient. None of the patients had recent blisters or rash. The clinical course was comparably mild in all patients. No permanent neurological sequelae were observed. Only the CSF total protein level was significantly higher in HHV DNA-positive than in HHV-negative patients.

HHV-7 in adults with drug-resistant epilepsy: a pathological role in hippocampal sclerosis?

BACKGROUND

Human herpesvirus-7 (HHV-7) is a β-herpesvirus associated with febrile seizures. No association between HHV-7 and epilepsy has been confirmed.

OBJECTIVES

The aim of this study was to investigate the presence of HHV-7 protein (KR4) in brain tissue from patients with drug-resistant epilepsy and to determine whether inflammatory molecules are activated in the presence of HHV-7 infection.

STUDY DESIGN

We used immunohistochemistry (IHC) to detect HHV-7 protein KR4 in samples from 305 patients with drug-resistant epilepsy. Liquid nitrogen-preserved hippocampal sclerosis (HS) samples from 63 of these patients were available, and we used nested polymerase chain reaction (PCR) to detect HHV-7 DNA. Inflammatory molecules including tumor necrosis factor-alpha (TNF-α), transforming growth factor-beta (TGF-β), interleukin-1 (IL-1) and interleukin-6 (IL-6) were identified by real-time PCR (rt-PCR) and IHC.

RESULTS AND CONCLUSIONS

The study sample included 201 male subjects. The mean age was 23.9, SD 6.2 years (range 15-45). HS was the pathology in 69 samples (23%). The HHV-7 protein was detected in 27 (9%) of the 305 samples and in none of the 42 controls. The factors associated with HHV-7 infection were HS (11/69), glial scar (8/58), arachnoid cyst (2/21), focal cortical dysplasia (2/31) and vascular malformation (4/52). HHV-7 antigen was distributed mainly in the cytoplasm of astrocyte and oligodendrocyte in HS samples. HHV-7 DNA was detected in 20 of the 63 nitrogen preserved HS samples. The expression of TGF-β was up-regulated in samples that were positive for the HHV-7 protein and was mainly detected in neurons. This finding suggests a possible association between HHV-7 positivity, activation of TGF-β and drug-resistant epilepsy, especially HS, but these data need to be replicated.

Human herpesvirus 6A infection in CD46 transgenic mice: viral persistence in the brain and increased production of proinflammatory chemokines via Toll-like receptor 9

Human herpesvirus 6 (HHV-6) is widely spread in the human population and has been associated with several neuroinflammatory diseases, including multiple sclerosis. To develop a small-animal model of HHV-6 infection, we analyzed the susceptibility of several lines of transgenic mice expressing human CD46, identified as a receptor for HHV-6. We showed that HHV-6A (GS) infection results in the expression of viral transcripts in primary brain glial cultures from CD46-expressing mice, while HHV-6B (Z29) infection was inefficient. HHV-6A DNA persisted for up to 9 months in the brain of CD46-expressing mice but not in the nontransgenic littermates, whereas HHV-6B DNA levels decreased rapidly after infection in all mice. Persistence in the brain was observed with infectious but not heat-inactivated HHV-6A. Immunohistological studies revealed the presence of infiltrating lymphocytes in periventricular areas of the brain of HHV-6A-infected mice. Furthermore, HHV-6A stimulated the production of a panel of proinflammatory chemokines in primary brain glial cultures, including CCL2, CCL5, and CXCL10, and induced the expression of CCL5 in the brains of HHV-6A-infected mice. HHV-6A-induced production of chemokines in the primary glial cultures was dependent on the stimulation of toll-like receptor 9 (TLR9). Finally, HHV-6A induced signaling through human TLR9 as well, extending observations from the murine model to human infection. Altogether, this study presents a first murine model for HHV-6A-induced brain infection and suggests a role for TLR9 in the HHV-6A-initiated production of proinflammatory chemokines in the brain, opening novel perspectives for the study of virus-associated neuropathology.

IMPORTANCE

HHV-6 infection has been related to neuroinflammatory diseases; however, the lack of a suitable small-animal infection model has considerably hampered further studies of HHV-6-induced neuropathogenesis. In this study, we have characterized a new model for HHV-6 infection in mice expressing the human CD46 protein. Infection of CD46 transgenic mice with HHV-6A resulted in long-term persistence of viral DNA in the brains of infected animals and was followed by lymphocyte infiltration and upregulation of the CCL5 chemokine in the absence of clinical signs of disease. The secretion of a panel of chemokines was increased after infection in primary murine brain glial cultures, and the HHV-6-induced chemokine expression was inhibited when TLR9 signaling was blocked. These results describe the first murine model for HHV-6A-induced brain infection and suggest the importance of the TLR9 pathway in HHV-6A-initiated neuroinflammation.

Human Herpesvirus 6 and Neuroinflammation

Human herpesvirus (HHV-) 6A and HHV-6B are two distinct β-herpesviruses which have been associated with various neurological diseases, including encephalitis, meningitis, epilepsy, and multiple sclerosis. Although the reactivation of both viruses is recognized as the cause of some neurological complications in conditions of immunosuppression, their involvement in neuroinflammatory diseases in immunocompetent people is still unclear, and the mechanisms involved have not been completely elucidated. Here, we review the available data providing evidence for the capacity of HHV-6A and -6B to infect the central nervous system and to induce proinflammatory responses by infected cells. We discuss the potential role of both viruses in neuroinflammatory pathologies and the mechanisms which could explain virus-induced neuropathogenesis.

Persistent infection of a gammaherpesvirus in the central nervous system

Human gammaherpesvirus infections of the central nervous system (CNS) have been linked to various neurological diseases. Murine gammaherpesvirus 68 (MHV-68), genetically related and biologically similar to human gammaherpesviruses, infects the CNS in laboratory mice. However, viral persistency of MHV-68 has not been studied following CNS infection. In this study, we undertook the noninvasive bioluminescence imaging of a recombinant MHV-68 expressing the firefly luciferase (M3FL) to monitor virus progression after CNS infection. The M3FL virus inoculated in the brain systemically spread to the abdominal area in bioluminescence imaging, which was further confirmed by detection of viral genome and transcripts. The disseminated wild-type virus established latency in the spleen. Moreover, the treatment of the infected mice with CsA induced reactivation of latent MHV-68 from the brain and the spleen. Our results suggest that MHV-68 may persist both inside and outside the CNS once it gains access to the CNS.

Survey for the presence of BK, JC, KI, WU and Merkel cell polyomaviruses in human brain tissues

BACKGROUND

Recently three previously unknown polyomaviruses (KI, WU and Merkel cell polyomaviruses) have been identified from human specimens. The spectrum of clinical manifestations and their tissue tropism are currently unknown. Since a member of this virus family, JC virus, is well-known for its capacity to establish latency in human brain tissue where reactivation in immunocompromised individuals can result in fatal progressive multifocal leukoencephalopathy, we sought to examine for the presence of all the five known human polyomaviruses in a series of human brain tissues.

OBJECTIVES

To investigate the possibility of neuropersistence of the newly identified human polyomaviruses.

STUDY DESIGN

Autopsy brain tissues were collected from 10 different brain regions of 30 individuals who died from diseases unrelated to viral infections. Nested PCR was used to assess the presence or absence of viral DNA.

RESULTS

Ten samples collected from five individuals were found to harbour JCV DNA. In contrast, none of the 300 brain tissues examined showed positive results for BK, KI, WU or Merkel cell polyomavirus.

CONCLUSION

The newly identified KI, WU and Merkel cell polyomaviruses either do not, or have a much lower neuropersistent potential compared to JCV.

Age-dependent pathogenesis of murine gammaherpesvirus 68 infection of the central nervous system

Gammaherpesvirus infection of the central nervous system (CNS) has been linked to various neurological diseases, including meningitis, encephalitis, and multiple sclerosis. However, little is known about the interactions between the virus and the CNS in vitro or in vivo. Murine gammaherpesvirus 68 (MHV-68 or (gamma)HV-68) is genetically related and biologically similar to human gammaherpesviruses, thereby providing a tractable animal model system in which to study both viral pathogenesis and replication. In the present study, we show the successful infection of cultured neuronal cells, microglia, and astrocytes with MHV-68 to various extents. Upon intracerebroventricular injection of a recombinant virus (MHV-68/LacZ) into 4-5-week-old and 9-10-week-old mice, the 4-5-week-old mice displayed high mortality within 5-7 days, while the majority of the 9-10-week-old mice survived until the end of the experimental period. Until a peak at 3-4 days post-infection, viral DNA replication and gene expression were similar in the brains of both mouse groups, but only the 9-10-week-old mice were able to subdue viral DNA replication and gene expression after 5 days post-infection. Pro-inflammatory cytokine mRNAs of tumor necrosis factor-alpha, interleukin 1beta, and interleukin 6 were highly induced in the brains of the 4-5-week-old mice, suggesting their possible contributions as neurotoxic factors in the agedependent control of MHV-68 replication of the CNS.

Human herpes virus 6B: a possible role in epilepsy?

Human herpes virus 6 (HHV6) infection is nearly ubiquitous in childhood and may include central nervous system invasion. There are two variants, HHV6A and HHV6B. Usually asymptomatic, it is associated with the common, self-limited childhood illness roseola infantum and rarely with more severe syndromes. In patients with immune compromise, subsequent reactivation of viral activity may lead to severe limbic encephalitis. HHV6 has been identified as a possible etiologic agent in multiple sclerosis, myocarditis, and encephalitis. A preponderance of evidence supports an association between HHV6 and febrile seizures. An ongoing multicenter study is investigating possible links between HHV6 infection, febrile status epilepticus, and development of mesial temporal sclerosis (MTS). Investigation of temporal lobectomy specimens showed evidence of active HHV6B but not HHV6A replication in hippocampal astrocytes in about two-thirds of patients with MTS but not other causes of epilepsy. It has been suggested that HHV6B may cause "excitotoxicity" by interfering with astrocyte excitatory amino acid transport. Although conventional inflammatory changes are not found in most MTS specimens, inflammatory modulators may play a role in neuronal injury leading to MTS as well. If the link between early viral infection, complex or prolonged febrile seizures, and later development of intractable temporal lobe epilepsy is confirmed, new therapeutic approaches to a common intractable epilepsy syndrome may be possible.

Central nervous system infections of herpesvirus family

Herpesviruses are one of the most common groups of pathogens causing central nervous system infections in humans. They mostly cause encephalitis, meningitis, or myelitis in immunocompetent and immunocompromised patients. Children, adults, and the elderly can all be affected. Although contrast-enhanced CT is more widely used for diagnosis, contrast-enhanced MR imaging combined with diffusion-weighted imaging is superior to CT in the detection of early changes and the real extent of the disease, and in assessing prognosis and monitoring response to antiviral treatment. More sophisticated techniques, such as MR spectroscopy and perfusion imaging, can aid in the differential diagnosis of herpesvirus infections from other tumoral, demyelinating, and ischemic processes.

The prevalence of human herpesvirus 6 in human sensory ganglia and its co-occurrence with alpha-herpesviruses

Human herpesvirus 6 (HHV-6) persists in the central nervous system, but its prevalence in the peripheral nervous system, a preferred latency site for herpesviruses, has not been studied. Using nested polymerase chain reaction (PCR), the authors determined the distribution of HHV-6 in human sensory ganglia. HHV-6 was present in 30% of trigeminal, 40% of geniculate, 25% of vestibular, and 55% of dorsal root ganglia. It co-occurred with alpha-herpesviruses (herpes simplex virus type 1 or varicella-zoster virus) in 91% of the ganglia. As HHV-6 positivity did not depend on the presence of inflammatory cells, known to harbor the virus, HHV-6 probably resides in the ganglia themselves.

Investigation of HSV-1, HSV-2, CMV, HHV-6 and HHV-8 DNA by real-time PCR in surgical resection materials of epilepsy patients with mesial temporal lobe sclerosis

OBJECTIVE

The objective of this study is to investigate the presence of viral DNAs of HSV-1, HSV-2, HHV-6, HHV-8, and CMV in hippocampus of the patients with mesial temporal lobe epilepsy (MTLE) syndrome.

METHODS

Pathological specimens were obtained from 33 patients with MTLE undergone temporal lobectomy with amygdalo-hippocampectomy due to intractable seizures. Autopsy materials from the hippocampus of 7 patients without neurological disease were used as controls. The data was also correlated with the clinical history of patients including febrile convulsions, age, and history of CNS infections. Real-time polymerase chain reaction method was performed for detection of DNAs of these viruses.

RESULTS

HHV-6, HSV-1 and HHV-8 were detected in the hippocampus of 3, 2 and 1 patients with MTLE respectively. None of the hippocampus of patients with MTLE was positive for DNA of HSV-2 and/or CMV. Three patients with positive HHV-6 DNAs had febrile convulsions and family history for epilepsy. None of our control specimens showed PCR positivity to any of the 5 tested viruses.

CONCLUSIONS

Our study is the first to report the presence of HHV-8 viral genome in the brain tissue of patient with MTLE. Viral DNAs were detected in a total of 18% of the patients in this study; we can conclude that activity of the latent virus in patients with hippocampal sclerosis should be more extensively studied to establish its role in active infection.

Differentiated human neural stem cells: a new ex vivo model to study HHV-6 infection of the central nervous system

BACKGROUND

HHV-6 is the etiologic agent of exanthem subitum, a pediatric illness that may be associated with clinical and laboratory signs of central nervous system involvement. The absence of suitable experimental models has so far hampered the elucidation of the mechanisms of HHV-6-mediated neural cell damage. Recently, the growing knowledge in neurobiology has permitted the establishment of long-term cultures of human neural stem cells (hNSC) that, by virtue of their self-renewal capacity and multipotentiality, provide a valuable tool for the study of neurodegenerative disorders.

OBJECTIVES AND STUDY DESIGN

We studied the effects of HHV-6 infection in differentiated cultures of hNSC derived from the telencephalic and diencephalic regions of a 13.5 week post conception (pcw) fetal brain. The prototypic HHV-6 strain GS (subgroup A) was used.

RESULTS

hNSC were differentiated ex vivo to obtain mixed cultures encompassing astrocytes, neurons and oligodendrocytes. These differentiated hNSC cultures were found to be susceptible to productive HHV-6A infection, resulting in the formation of syncytia associated with phenotypic alterations.

CONCLUSION

These results demonstrate that hNSC may provide a physiologically relevant model to investigate the pathogenic role of HHV-6 in central nervous system disorders.

Infection of murine oligodendroglial precursor cells with Human Herpesvirus 6 (HHV-6)--establishment of a murine in vitro model

BACKGROUND

Human Herpesvirus 6 was previously demonstrated to infect human oligodendroglial precursor cells (OPCs) in vitro causing cell cycle arrest and premature differentiation with consequent loss of the precursor pool.

OBJECTIVES

To develop an in vitro murine OPC model to study the cell cycle and differentiation effects of HHV-6 in more readily available, genetically well-defined cells free of the risk of contamination with human herpesviruses.

STUDY DESIGN

Murine OPCs were exposed to infectious HHV-6A or HHV-6B and analyzed for production of viral transcripts, particles, and replicating virus. FACS analysis and specific markers were used to evaluate effects on cell cycling and differentiation.

RESULTS

HHV-6 infection of murine OPCs resulted in production of both immediate-early and some late transcripts but no replicating virus by TaqMan quantitative PCR or electron microscopy. Both a specific G1/S cell cycle arrest and premature loss of OPCs through differentiation into oligodendrocytes as previously seen with human precursors were recapitulated.

CONCLUSIONS

Infection of murine OPCs by HHV-6 reproduces the critical phenotypes of cell cycle arrest and altered differentiation seen in human cells. The murine system provides a highly defined, accessible, and reproducible source of cells permitting the elucidation of specific viral and cell cycle genes involved in CNS viral infections of OPCs.

Update on human herpesvirus 6 biology, clinical features, and therapy

Human herpesvirus 6 (HHV-6) is a betaherpesvirus that is closely related to human cytomegalovirus. It was discovered in 1986, and HHV-6 literature has expanded considerably in the past 10 years. We here present an up-to-date and complete overview of the recent developments concerning HHV-6 biological features, clinical associations, and therapeutic approaches. HHV-6 gene expression regulation and gene products have been systematically characterized, and the multiple interactions between HHV-6 and the host immune system have been explored. Moreover, the discovery of the cellular receptor for HHV-6, CD46, has shed a new light on HHV-6 cell tropism. Furthermore, the in vitro interactions between HHV-6 and other viruses, particularly human immunodeficiency virus, and their relevance for the in vivo situation are discussed, as well as the transactivating capacities of several HHV-6 proteins. The insight into the clinical spectrum of HHV-6 is still evolving and, apart from being recognized as a major pathogen in transplant recipients (as exemplified by the rising number of prospective clinical studies), its role in central nervous system disease has become increasingly apparent. Finally, we present an overview of therapeutic options for HHV-6 therapy (including modes of action and resistance mechanisms).

Herpesviral DNA in brain tissue from patients with temporal lobe epilepsy

OBJECTIVES

Presence of DNA from six herpesviruses were examined in brain tissue from patients operated for temporal lobe epilepsy.

MATERIAL AND METHODS

A total of 19 Canadian patients (I) with a median age of 22 years, 17 Swedish patients (II) with a median age of 14 years and a reference group comprising 12 individuals were studied. Presence of herpesviral DNA was detected by nested polymerase chain reaction.

RESULTS

Of three children with Rasmussen's encephalitis, Cytomegalovirus (CMV) DNA was found in two, and human herpesvirus type 6 DNA in two. In six children with ganglioglioma, Epstein-Barr virus (EBV) was detected in four. CMV DNA was found significantly more in group I compared with II, while the reverse occurred with EBV DNA. Malformations of cortical development were found significantly more in group II compared with I.

CONCLUSION

Detection of DNA from some herpesviruses in epileptic brain tissue may possibly be associated with distinct clinical conditions, but factors such as age and malformations of cortical development should also be considered.

Detection of human herpesvirus-6 in mesial temporal lobe epilepsy surgical brain resections

BACKGROUND

Human herpesvirus-6 (HHV-6), a ubiquitous beta-herpesvirus, is the causative agent of roseola infantum and has been associated with a number of neurologic disorders including seizures, encephalitis/meningitis, and multiple sclerosis. Although the role of HHV-6 in human CNS disease remains to be fully defined, a number of studies have suggested that the CNS can be a site for persistent HHV-6 infection.

OBJECTIVE

To characterize the extent and distribution of HHV-6 in human glial cells from surgical brain resections of patients with mesial temporal lobe epilepsy (MTLE).

METHOD

Brain samples from eight patients with MTLE and seven patients with neocortical epilepsy (NE) undergoing surgical resection were quantitatively analyzed for the presence of HHV-6 DNA using a virus-specific real-time PCR assay. HHV-6 expression was also characterized by western blot analysis and in situ immunohistochemistry (IHC). In addition, HHV-6-reactive cells were analyzed for expression of glial fibrillary acidic protein (GFAP) by double immunofluorescence.

RESULTS

DNA obtained from four of eight patients with MTLE had significantly elevated levels of HHV-6 as quantified by real-time PCR. HHV-6 was not amplified in any of the seven patients with NE undergoing surgery. The highest levels of HHV-6 were demonstrated in hippocampal sections (up to 23,079 copies/10(6) cells) and subtyped as HHV-6B. Expression of HHV-6 was confirmed by western blot analysis and IHC. HHV-6 was co-localized to GFAP-positive cells that morphologically appeared to be astrocytes.

CONCLUSIONS

HHV-6B is present in brain specimens from a subset of patients with MTLE and localized to astrocytes in the absence of inflammation. The amplification of HHV-6 from hippocampal and temporal lobe astrocytes of MTLE warrants further investigation into the possible role of HHV-6 in the development of MTLE.

Human T-lymphotropic virus type II and neurological disease

Human T-lymphotropic virus type I (HTLV-I) and type II (HTLV-II) are closely related retroviruses with similar biological properties and common modes of transmission. HTLV-I infection is endemic in well-defined geographic regions, and it is estimated that some 20 million individuals are infected worldwide. Although most infected individuals are asymptomatic carriers, some 2 to 5% will develop a chronic encephalomyelopathy, HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). In contrast with HTLV-I, the role of HTLV-II in the development of neurological disorders is much less clear. HTLV-II is endemic in many native Amerindian groups and epidemic in injecting drug users (IDUs) worldwide. To evaluate the role of HTLV-II in neurological disease, we have critically reviewed all reported cases of HTLV-II-associated disorders. This has confirmed that although rare infection is associated with a disorder clinically similar or identical to HAM/TSP. However, most reports that have attributed infection to a range of other neurological disorders are difficult to evaluate in that in many cases either the association appears to be fortuitous or the presentations were confounded by a background of concomitant human immunodeficiency virus-1 infection and/or active IDU. In view of the many HTLV-II-infected individuals in urban areas of North America and Europe, neurologists should be aware of the potential clinical consequences of this infection.

Virus del herpes humano tipo 6 y tipo 7 en receptores de trasplantes

Recent years have witnessed a growing interest in the role of human herpesvirus (HHV) type 6 and type 7 as emerging pathogens or copathogens in transplant recipients. Both HHV-6 and HHV-7 belong to the beta-herpesvirus family and are closely related to another member of the family, cytomegalovirus. After the primary infection, these viruses remain latent in the human host and can reactivate after transplantation. Various clinical processes such as fever, rash, pneumonitis, encephalitis, hepatitis, and myelosuppression have been described in association with herpesvirus. Moreover, a growing body of evidence suggests that the major impact of HHV-6 and HHV-7 reactivation in transplantation is related to indirect effects, such as their association with cytomegalovirus disease, increased opportunistic infections, and graft dysfunction and rejection. The pathogenesis of HHV-6 and HHV-7 during the post-transplantation period, the methods used for their diagnosis, and the evaluation of antiviral drugs and strategies for their prevention and treatment are now the subject of extensive research.

Human herpesvirus-7 infection of the CNS with acute myelitis in an adult bone marrow recipient

The beta-herpesviruses, human herpesviruses-6 and -7 (HHV-6 and HHV-7), are closely related and have very similar biological behaviour. While HHV-6 is associated with encephalitis in immunosuppressed adults, HHV-7 is not recognised as a cause of neurological disease in such patients. This report describes the identification of a reactivated HHV-7 infection in the cerebrospinal fluid of an adult who presented with an acute myelitis 11 months after unrelated donor bone marrow transplant.

Case report: human herpesvirus 7 associated fatal encephalitis in a peripheral blood stem cell transplant recipient

Previous studies have suggested a neuroinvasive and neuropersistent potential of human herpesvirus 7 (HHV-7). In this report, a case of fatal encephalitis is described and its association with HHV-7 infection is discussed. An 8-year-old girl received a peripheral blood stem cell transplant for relapsed acute lymphoblastic leukaemia. The post-transplant period was uneventful and a course of intrathecal chemotherapy was given on Day-30. On Day-41, she developed acute encephalopathy with diplopia and nystagmus. She ran a rapid downhill course and succumbed despite antiviral treatment. The only positive pathological finding was the multiple microscopic foci of haemorrhage associated with neuronal degeneration detected in the brain stem. All microbiological investigations were negative, except for the presence of HHV-7 DNA in cerebrospinal fluid and brain stem tissue samples.

Viral studies in the cerebrospinal fluid in subacute sclerosing panencephalitis

OBJECTIVES

The pathogenesis of subacute sclerosing panencephalitis (SSPE), and particularly, the cause of measles virus (MV) reactivation following a latent period after primary measles infection is unknown. The hypothesis of other viruses contributing to the pathogenesis of SSPE by affecting the in vivo state of MV was investigated.

METHODS

We examined the cerebrospinal fluid of SSPE patients (n=43) for DNA or RNA and antibodies against HSV type 1 and 2, EBV, CMV, VZV, Hepatitis B, Hepatitis C, JC virus, human herpesvirus (HHV)-6, HHV-7, HHV-8, HTLV-1, and HTLV-2. We compared the findings with those of patients with other neurological disorders (n=39).

RESULTS

CMV DNA and HSV type 1 IgG were found more frequently in SSPE patients. Other positive results were at similar incidence in SSPE and control groups. The clinical features of SSPE cases with and without positive viral tests did not differ from each other.

CONCLUSION

These data do not support a specific role for these agents in SSPE, but imply that the passage of some viruses to the CNS and local antibody synthesis may be facilitated by inflammation. The persistence or reactivation of MV in SSPE may be related to other factors pertaining to the host or environment.

The pathogenesis of febrile seizures: is there a role for specific infections?

Although fever is regarded as the main trigger in the pathogenesis of febrile seizures (FS), it is not supposed to be the unique causative factor. In FS, there is a strong familial predisposition. This does not exclude infections as a causative factor because subtle genetic polymorphisms have been demonstrated to affect the course of infections. We review the literature on: (1) the role of fever, especially the height of temperature, its cause, and metabolic effects induced by temperature; (2) the role of heredity; (3) the role of cytokines which play a role in the induction of fever; and (4) the role of type of infection, with emphasis on newly identified agents and improved diagnostic techniques. With modern molecular techniques such as PCR, viruses have been detected in the CSF far more often than previously thought, even in the absence of pleocytosis of the CSF. This makes it difficult to distinguish FS from acute encephalitis. FS may be caused by neuroinvasion or intracerebral activation of viruses. Further studies should focus on these options because therapeutic intervention is possible and may prevent late sequelae such as recurrent FS and subsequent epilepsy.

HHV-6 A- or B-specific P41 antigens do not reveal virus variant-specific IgG or IgM responses in human serum

The etiology of multiple sclerosis (MS) remains unknown, but there are indications of a role of human herpesvirus 6 (HHV-6), especially variant A, in the pathogenesis. Higher serum antibody reactivity against an HHV-6 early protein, p41, has been found in MS cases than in controls. The antigen, however, was purified from infected cells with a monoclonal antibody also reactive with a protein (p38) likely to be of cellular origin. To avoid serological crossreactivity with the cellular protein, recombinant p41 proteins from HHV-6A strain GS and HHV-6B strain Z29 were expressed as glutathione-S-transferase fusion proteins (p41-GST), and used as antigens in an enzyme-linked immunosorbent assay (ELISA). p41 variant specific monoclonal antibodies reacted strongly with the respective recombinant proteins. Serum IgM and IgG reactivities with the recombinant p41 antigens were analysed in patients with manifest MS, patients with optic neuritis, patients with other neurological diseases, and in one group of healthy controls. All sera were HHV-6 IgG seropositive by immunofluorescence. The serum IgM or IgG reactivities against the recombinant p41 antigens did not differ significantly between the groups, and the reactivities against the variant A and B antigens were identical. In many samples, the reactivity was very low. The results indicate that p41 is not an optimal target for HHV-6 serology studies, and that the data obtained with the p41 antigen prepared from infected cells (possibly including also p38) should be interpreted with caution.

Polymerase chain reaction as a diagnostic adjunct in herpesvirus infections of the nervous system

Polymerase chain reaction (PCR) is a powerful technique that allows detection of minute quantities of DNA or RNA in cerebrospinal fluid (CSF), vesicle and endoneurial fluids, blood, fresh-frozen, and even formalin-fixed tissues. Various infectious agents can be detected with high specificity and sensitivity, including bacteria, parasites, rickettsia and viruses. PCR analysis of CSF has revolutionized the diagnosis of nervous system viral infections, particularly those caused by human herpesviruses (HHV), and has now replaced brain biopsy as the gold standard for diagnosis of herpes simplex virus (HSV) encephalitis. PCR analysis of both CSF and nervous system tissues has also broadened our understanding of the spectrum of disease caused by HSV-1 and -2, cytomegalovirus (CMV), Epstein-Barr virus (EBV), varicella zoster virus (VZV), and HHV-6. Nonetheless, positive tissue PCR results must be interpreted cautiously, especially in cases that lack corroborating clinical and neuropathologic evidence of infection. Moreover, positive PCR results from tissues do not distinguish latent from productive (lytic) viral infections. In several neurological diseases, negative PCR results have provided strong evidence against a role for herpesviruses as the causative agents. This review focuses on the use of PCR tests to diagnose HSV and VZV infections of the nervous system.

Fifth (human parvovirus) and sixth (herpesvirus 6) diseases

Fifth (erythema infectiosum) and sixth (roseola infantum) diseases are common rash illnesses of childhood that have long been recognized in clinical medicine. The discovery of the viruses that cause these illnesses has revealed relationships with other syndromes. Primary infection with the agent of erythema infectiosum, human parvovirus B19, is associated with transient aplastic crisis in hemolytic anemia, arthropathy in adults, chronic anemia in immunocompromised patients, and nonimmune fetal hydrops in pregnant women. The only documented illness associated with primary infection with human herpesvirus 6 is roseola or exanthema subitum in young children. However, reactivated infections in adults and immunocompromised patients may be associated with serious illness such as encephalitis/encephalopathy, and bone marrow suppression leading to transplant failure or graft-versus-host disease. Diagnostic studies for both viruses have been limited, although reliable serologic tests for human parvovirus B19 have recently become available. Diagnosis of human herpesvirus 6 remains problematic, because current tests cannot differentiate primary from reactivated disease. This is more of an issue for the putative relationship of these viruses to more chronic conditions, such as rheumatologic disease for human parvovirus B19 and multiple sclerosis for human herpesvirus 6. The relationship between the viruses and these conditions remains controversial, and better diagnostic tests and further information on viral pathogenesis for both viruses are required in order to make a reliable judgment in this regard.

Prevalence and distribution of human herpesvirus 6 variants A and B in adult human brain

The presence of human herpesvirus 6 (HHV-6) in brain tissues of 40 consecutive post-mortem cases was examined. For each case, autopsy samples were collected from the cerebellum, frontal, temporal, parietal and occipital lobes of both sides of the brain. HHV-6 DNA was detected by nested polymerase chain reaction and characterised into variants A and B. Overall, 97/400 (24.3%) samples were positive for HHV-6 DNA with 16 being variant A and 81 being variant B, but none of the samples harboured both variants. When analysed by patient, 34/40 (85%) had HHV-6 DNA detected in the brain. The viral DNA positivity did not show significant variation with gender and age. Four patients harboured variant A, 23 harboured variant B, and seven had both variants at different positions. The results indicate that both HHV-6A and HHV-6B are neurotropic and human brain may be another site for latency. HHV-6B was detected in brain tissues of a majority (75%) of the studied population and with a widespread distribution within the brain. Although the observed prevalence of HHV-6A in brain is lower (27.5%), in view of its lower seroprevalence, the neuroinvasive potential of variant A may be comparable to that of variant B. Although both variants are potential pathogens for the nervous system, the fact that they can exist, probably for most of the time, as commensals in human brain needs to be considered when interpreting their roles in neuropathology.

Viruses and multiple sclerosis

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system whose cause is still unknown. Many findings suggest an infectious etiology or, at least, that infectious agents in association with host genetic factors may play a role in the pathogenesis of this disease. Accumulating data, including animal models, human models of virus induced demyelination, epidemiologic, and laboratory findings, demonstrate that viruses and host genetic factors can interact to cause immune-mediated demyelination. While many viruses have been postulated as a possible cause of MS, to date, no "MS virus" has been definitively shown to be associated with this disease. Alternatively, ubiquitous viruses are being considered as the environmental "triggers" that have been postulated to be involved in the MS disease process. We will focus on recent studies with human herpesvirus 6 and MS as how a common virus may be associated with this disorder in a subset of infected individuals.

Prevalence and distribution of human herpesvirus 7 in normal brain

Although it has been recognised that human herpesvirus 7 (HHV-7) establishes latent infection in CD4+ T lymphocytes and productive infection in salivary glands, recent data suggest that its in vivo tropism may be more widespread. In this study, the prevalence and distribution of HHV-7 in brain tissues of 30 consecutive post-mortems were examined by nested polymerase chain reaction. For each post-mortem, 10 fresh autopsy tissue samples were collected respectively from the cerebellum, frontal, temporal, parietal, and occipital lobes of both cerebral hemispheres. These patients were aged from 20-95 years (mean = 61.4, SD = 20.2) with a male:female ratio of 2:1. Three patients died of intracranial haemorrhage, the others died of causes unrelated to the central nervous system. Overall, 5% (15/300) of the brain tissue samples were positive for HHV-7 DNA. The positive rates with respect to anatomical positions were similar (0-3/30). When analysed by patient, 36.7% (11/30) were HHV-7 DNA positive. The viral DNA-positive and -negative groups did not show a significant difference in gender or age distribution. The majority (81.8%) of viral DNA-positive patients had HHV-7 DNA detected at only one anatomical position; only two patients had viral DNA detected simultaneously at three anatomical sites. These results suggest that HHV-7 persists in brain tissues of a substantial proportion of the adult population, and in most individuals, its distribution is probably confined to one site rather than pervasive. Further studies to elucidate the role of this ubiquitous virus in neuropathology are warranted.