Fatal encephalitis/encephalopathy in primary human herpesvirus-6 infection

Metagenomic Next-Generation Sequencing vs. Traditional Microbiological Tests for Diagnosing Varicella-Zoster Virus Central Nervous System Infection

Background

Unbiased metagenomic next-generation sequencing (mNGS) detects pathogens in a target-independent manner. It is not well-understood whether mNGS has comparable sensitivity to target-dependent nucleic acid test for pathogen identification.

Methods

This study included 31 patients with chickenpox and neurological symptoms for screening of possible varicella-zoster virus (VZV) central nervous system (CNS) infection. Microbiological diagnosing of VZV cerebrospinal fluid (CSF) infection was performed on stored CSF samples using mNGS, quantitative and qualitative VZV-specific PCR assays, and VZV IgM antibodies test.

Results

The median age was 30.0 [interquartile range (IQR), 24.3–33.3] years. 51.6% of the patients were men. About 80.6% of the patients had normal CSF white blood cell counts (≤ 5 × 10⁶/L). VZV IgM antibodies presented in 16.1% of the CSF samples, and nucleic acids were detectable in 16.1 and 9.7% using two different VZV-specific real-time PCR protocols. Intriguingly, maximal identification of VZV elements was achieved by CSF mNGS (p = 0.001 and p = 007; compared with qualitative PCR and VZV IgM antibody test, respectively), with sequence reads of VZV being reported in 51.6% (16/31) of the CSF samples. All VZV PCR positive samples were positive when analyzed by mNGS. Of note, human betaherpesvirus 6A with clinical significance was unexpectedly detected in one CSF sample.

Conclusions

Our study suggests that CSF mNGS may have higher sensitivity for VZV detection than CSF VZV PCR and antibody tests, and has the advantage of identifying unexpected pathogens.

Hippocampal Atrophy in Pediatric Transplant Recipients with Human Herpesvirus 6B

The aim of this study was to determine whether human herpesvirus 6B (HHV-6B) infection can impair the hippocampus in pediatric hematopoietic stem cell transplant (HSCT) recipients. Study subjects were pediatric HSCT recipients monitored for HHV-6B infection who underwent brain MRI before and after transplantation. Volumetric analysis of the hippocampus was performed. Of the 107 patients that received HSCT at Nagoya University Hospital Between July 2008 and April 2014, 20 were eligible for volumetric analysis. Eight patients had HHV-6B infection, of whom two had encephalopathy at the time of HHV-6B infection. None of the 12 patients without HHV-6B infection had encephalopathy. The median ratio of the right hippocampal volume from before to after transplantation was 0.93 in patients with HHV-6B infection and 1.02 in without HHV-6B infection (p = 0.007). The median ratio of the left hippocampal volume ratio in patients with and without HHV-6B infection was 0.92 and 1.00, respectively (p = 0.003). Among the eight patients with HHV-6B infection, four had a marked reduction in hippocampal volume (volume ratio < 0.90). Only one of these patients had neurological symptoms at the time of HHV-6B infection. The reduction in the hippocampal volume ratio was higher in pediatric HSCT recipients with HHV-6B infection than those without viral infection. Neurological follow-up may be required for pediatric HSCT recipients with HHV-6B infection.

Towards the development of a human in vitro model of the blood-brain barrier for virus-associated acute encephalopathy: assessment of the time- and concentration-dependent effects of TNF-α on paracellular tightness

The pathogenesis of virus-associated acute encephalopathy (VAE) involves brain edema caused by disruption of the blood-brain barrier (BBB). We aimed to develop an in vitro VAE model using an in vitro BBB model, to evaluate the dynamics of vascular dysfunction caused by tumor necrosis factor (TNF)-α. A co-culture model, consisting of Transwell®-grown human brain microvascular endothelial cells and pericytes, was treated with serially diluted TNF-α. Transendothelial electrical resistance (TER) was measured using cellZscope®. A permeability assay, using fluorescein isothiocyanate-conjugated sodium or dextran, was performed. Changes in claudin-5 localization and expression after TNF-α treatment were observed using immunofluorescence staining and western blot analysis. The TER decreased and permeability increased after TNF-α treatment; recovery time was dependent on TNF-α concentration. Claudin-5 was delocalized after TNF-α treatment and recovered in a TNF-α concentration-dependent manner. The expression of claudin-5 decreased 24 h after the TNF-α treatment and completely recovered 48 h after TNF-α treatment. Claudin-5 delocalization was likely associated with vascular hyperpermeability. To conclude, we evaluated vascular endothelial cell permeability and injury in VAE using an in vitro BBB model treated with TNF-α. This system can be useful for developing novel therapeutic strategies for VAE and designing treatments that target vascular permeability.

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.

Clinical Features of Complex Febrile Seizure Caused by Primary Human Herpesvirus 6B Infection

BACKGROUND

It is well known that febrile seizures are commonly occur in children with exanthem subitum. In this study, we compared the clinical features and backgrounds of patients with complex febrile seizures with and without primary human herpesvirus 6B infection.

METHODS

Sixty-two patients were enrolled after experiencing their first febrile seizure. Primary human herpesvirus 6B infection was confirmed when human herpesvirus 6B DNA was detected and human herpesvirus 6B antibody was negative in serum obtained during the acute phase of infection. Patient age, gender, and features of seizures were evaluated between patients with and without human herpesvirus 6B infection.

RESULTS

Thirty patients with complex febrile seizure were diagnosed with primary human herpesvirus 6B infection. Those with primary human herpesvirus 6B infection (median, 13 months; range, seven to 39 months) were significantly younger than those without primary human herpesvirus 6B infection (median, 19 months; range, 10 to 59 months) (P = 0.001), and the proportion of males was significantly higher in patients without primary human herpesvirus 6B infection (male/female, 25/7) than in those with the infection (male/female, 14/16) (P = 0.017). An interval between fever onset and seizures of more than 24 hours was significantly more common in patients with primary human herpesvirus 6B infection (15 of the 30 patients) than in those without primary HHV-6B infection (two of 32 patients) (P < 0.001).

CONCLUSIONS

A younger age at onset, a different gender ratio compared with febrile seizure due to other causes, and the length of interval between fever and seizures were features of complex febrile seizure associated human herpesvirus 6B infection. These findings may suggest a mechanism of complex febrile seizure onset different from that due to other causes.

Central Nervous System Complications due to Human Herpesvirus 6 Infection in Pediatric Age Group

Human herpesvirus 6 (HHV-6) has been demonstrated to be a neurotropic virus and has been linked to several neurological complications associated with a wide range of clinical outcomes. Here, we present data from immunocompetent children with a central neurological condition and intrathecal DNA detection of HHV-6 virus. Through these cases, physiopathology, investigations, and outcome of the disease will be described. Finally, specific treatment will be discussed.

HHV-6-Associated Neurological Disease in Children: Epidemiologic, Clinical, Diagnostic, and Treatment Considerations

Human herpesviruses 6A and 6B, often referred to collectively as human herpesvirus 6, are a pair of beta-herpesviruses known to cause a variety of clinical syndromes in both immunocompetent and immunocompromised individuals. Most humans are infected with human herpesvirus 6B, and many with human herpesvirus 6A. Primary infection typically occurs in early childhood, although large-scale reviews on the topic are limited. Herein, the authors explore the clinical manifestations of human herpesvirus 6-associated disease in both immunocompetent and immunocompromised pediatric patients, the risk factors for development of human herpesvirus 6-associated neurological disease, the risk of autoimmunity associated with development of active or latent infection, the relevance of human herpesvirus 6-specific diagnostic tests, and the medications used to treat human herpesvirus 6. The goal of this review is to improve the current understanding of human herpesvirus 6 in pediatric populations and to examine the most effective diagnostic and therapeutic interventions in this disease state.

Human inborn errors of immunity to herpes viruses

Infections with any of the nine human herpes viruses (HHV) can be asymptomatic or life-threatening. The study of patients with severe diseases caused by HHVs, in the absence of overt acquired immunodeficiency, has led to the discovery or diagnosis of various inborn errors of immunity. The related inborn errors of adaptive immunity disrupt α/β T-cell rather than B-cell immunity. Affected patients typically develop HHV infections in the context of other infectious diseases. However, this is not always the case, as illustrated by inborn errors of SAP-dependent T-cell immunity to EBV-infected B cells. The related inborn errors of innate immunity disrupt leukocytes other than T and B cells, non-hematopoietic cells, or both. Patients typically develop only a single type of infection due to HHV, although, again, this is not always the case, as illustrated by inborn errors of TLR3 immunity resulting in HSV1 encephalitis in some patients and influenza pneumonitis in others. Most severe HHV infections in otherwise healthy patients remains unexplained. The forward human genetic dissection of isolated and syndromic HHV-driven illnesses will establish the molecular and cellular basis of protective immunity to HHVs, paving the way for novel diagnosis and management strategies.

Clinical course of human herpesvirus 6 infection in pediatric living donor liver transplantation

Differentiation between active and latent viral infection is critical for analysis of HHV-6-associated disease. HHV-6 infection has been associated with several clinical manifestations; however, the precise role of HHV-6 in pediatric LDLT remains unclear. This retrospective cohort study included 33 pediatric patients who received LDLT. All of the recipients were monitored for HHV-6 infection using viral isolation and real-time PCR. HHV-6 infection was observed in 14 of 33 (42.4%) recipients, and HHV-6B infection occurred within 2 weeks after LDLT in 10 of 14 (71.4%) recipients. HHV-6 was isolated from 10 of 33 (30.3%) recipients. Multivariate analysis showed that independent predictors of HHV-6B infection were age (OR 0.975; 95% CI 0.943-0.999; P = .041), PELD (OR 1.091; P = .038), and biliary atresia (OR 16.48; P = .035). The occurrence of unexplained fever was significantly higher in recipients with HHV-6B infection (11/14) compared with uninfected recipients (6/19) (P = .013). Additionally, ALT levels at 8 and 9 weeks after transplantation were significantly higher in the recipients with HHV-6B infection. Younger age, high MELD/PELD score, and biliary atresia as an underlying disease were identified as risk factors for viral infection.

Chemokines encoded by herpesviruses

Viruses use diverse strategies to elude the immune system, including copying and repurposing host cytokine and cytokine receptor genes. For herpesviruses, the chemokine system of chemotactic cytokines and receptors is a common source of copied genes. Here, we review the current state of knowledge about herpesvirus-encoded chemokines and discuss their possible roles in viral pathogenesis, as well as their clinical potential as novel anti-inflammatory agents or targets for new antiviral strategies.

Roseolovirus-associated encephalitis in immunocompetent and immunocompromised individuals

The roseoloviruses, human herpesvirus (HHV)-6A, HHV-6B, and HHV-7, can cause severe encephalitis or encephalopathy. In immunocompetent children, primary HHV-6B infection is occasionally accompanied by diverse clinical forms of encephalitis. Roseolovirus coinfections with heterologous viruses and delayed primary HHV-7 infection in immunocompetent adults result in very severe neurological and generalized symptoms. Recovery from neurological sequelae is slow and sometimes incomplete. In immunocompromised patients with underlying hematological malignancies and transplantation, frequent single or simultaneous reactivation of roseoloviruses elicit severe, lethal organ dysfunctions, including damages in the limbic system, brain stem, and hippocampus. Most cases have been due to HHV-6B with HHV-6A accounting for 2-3%. The most severe manifestation of HHV-6B reactivation is post-transplantation limbic encephalitis. Seizures, cognitive problems, and abnormal EEG are common. Major risk factors for HHV-6B-associated encephalitis include unrelated cord blood cell transplantation and repeated hematopoietic stem cell transplantation. Rare genetic disorders, male gender, certain HLA constellation, and immune tolerance to replicating HHV-6 in persons carrying chromosomally integrated HHV-6 might also predispose an individual to roseolovirus-associated brain damage. At this time, little is known about the risk factors for HHV-7-associated encephalitis. Intrathecal glial cell destruction due to virus replication, overexpression of proinflammatory cytokines, and viral mimicry of chemokines all contribute to brain dysfunction. High virus load in the cerebrospinal fluid, hippocampal astrogliosis, and viral protein expression in HHV-6B-associated cases and multiple microscopic neuronal degeneration in HHV-7-associated cases are typical laboratory findings. Early empirical therapy with ganciclovir or foscarnet might save the life of a patient with roseolovirus-associated encephalitis.

Update on infections with human herpesviruses 6A, 6B, and 7

Human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, HHV-7) are genetically related to cytomegalovirus. They belong to the Roseolovirus genus and to the Betaherpesvirinae subfamily. They infect T cells, monocytes-macrophages, epithelial cells, and central nervous system cells. These viruses are ubiquitous and are responsible for lifelong chronic infections, most often asymptomatic, in the vast majority of the general adult population. HHV-6B is responsible for exanthema subitum, which is a benign disease of infants. HHV-6A and HHV-6B also cause opportunistic infections in immunocompromised patients: encephalitis, hepatitis, bone marrow suppression, colitis, and pneumonitis. Their etiological role in chronic diseases such as multiple sclerosis, cardiomyopathy, and thyroiditis is still controversial. The pathogenicity of HHV-7 is less clear and seems to be much more restricted. Chromosomal integration of HHV-6A and HHV-6B is transmissible from parents to offspring and observed in about 1% of the general population. This integration raises the question of potential associated diseases and can be a confounding factor for the diagnosis of active infections by both viruses. The diagnosis of HHV-6A, HHV-6B, and HHV-7 infections is rather based on gene amplification (PCR), which allows for the detection and quantification of the viral genome, than on serology, which is mainly indicated in case of primary infection. Ganciclovir, foscarnet, and cidofovir inhibit the replication of HHV-6A, HHV-6B, and HHV-7. Severe infections may thus be treated but these therapeutic indications are still poorly defined.

Crystal Structure of Human Herpesvirus 6B Tegument Protein U14

The tegument protein U14 of human herpesvirus 6B (HHV-6B) constitutes the viral virion structure and is essential for viral growth. To define the characteristics and functions of U14, we determined the crystal structure of the N-terminal domain of HHV-6B U14 (U14-NTD) at 1.85 Å resolution. U14-NTD forms an elongated helix-rich fold with a protruding β hairpin. U14-NTD exists as a dimer exhibiting broad electrostatic interactions and a network of hydrogen bonds. This is first report of the crystal structure and dimerization of HHV-6B U14. The surface of the U14-NTD dimer reveals multiple clusters of negatively- and positively-charged residues that coincide with potential functional sites of U14. Three successive residues, L424, E425 and V426, which relate to viral growth, reside on the β hairpin close to the dimer's two-fold axis. The hydrophobic side-chains of L424 and V426 that constitute a part of a hydrophobic patch are solvent-exposed, indicating the possibility that the β hairpin region is a key functional site of HHV-6 U14. Structure-based sequence comparison suggests that U14-NTD corresponds to the core fold conserved among U14 homologs, human herpesvirus 7 U14, and human cytomegalovirus UL25 and UL35, although dimerization appears to be a specific feature of the U14 group.

Human herpesvirus 6B (HHV-6B), a causative agent of exanthema subitum for children and immunocompromised adults, encodes numerous tegument proteins that constitute the viral matrix. HHV-6B U14 is a tegument protein essential for viral propagation, and additionally it interacts with host factors such as tumor suppressor p53 and cellular protein EDD, thereby regulating host cell responses. Here, we report the molecular structure of HHV-6B U14 at an atomic resolution. The N-terminal domain of U14 (U14-NTD) adopts an elongated, helix-rich fold without any significant overall similarity to known structures. U14-NTD forms a 100 kDa homodimer through electrostatic interactions and a wide hydrogen bond network. The U14-NTD homodimer displays four clusters of electrostatic potential with deep grooves, implying multiple binding sites for other viral or host proteins. U14-NTD corresponds to the core fold shared by homologous proteins of human herpesvirus 7 (HHV-7) and of human cytomegalovirus, although dimerization seems to be specific to HHV-6 and HHV-7. The U14-NTD structure provides clues to promote further analysis on the role and behavior of U14 in the pathogenesis of HHV-6. It also leads to a comprehensive understanding of the U14 homologs in beta herpesviruses, and furthermore contributes to the overall knowledge about tegument proteins in herpesviruses.

Virus-Induced Demyelination: The Case for Virus(es) in Multiple Sclerosis

Multiple Sclerosis (MS) is the most common demyelinating disease of man with over 400,000 cases in the United States and over 2.5 million cases worldwide. There are over 64,000 citations in Pubmed dating back as far as 1887. Much has been learned over the past 129 years with a recent burst in therapeutic options (mostly anti-inflammatory) with newer medications in development that are neuroprotective and/or neuroreparative. However, with all these advancements the cause of MS remains elusive. There is a clear interplay of genetic, immunologic, and environmental factors that influences both the development and progression of this disorder. This chapter will give a brief overview of the history and pathogenesis of MS with attention to how host immune responses in genetically susceptible individuals contribute to the MS disease process. In addition, we will explore the role of infectious agents in MS as potential “triggers” of disease. Models of virus-induced demyelination will be discussed, with an emphasis on the recent interest in human herpesviruses and the role they may play in MS disease pathogenesis. Although we remain circumspect as to the role of any microbial pathogen in MS, we suggest that only through well-controlled serological, cellular immune, molecular, and animal studies we will be able to identify candidate agents. Ultimately, clinical interventional trials that either target a specific pathogen or class of pathogens will be required to make definitive links between the suspected agent and MS.

The human herpesvirus 6 U21-U24 gene cluster is dispensable for virus growth

Human herpesvirus 6 (HHV-6) is a T-lymphotrophic virus belongs to the genus Roseolovirus within the beta herpesvirus subfamily. The U20-U24 gene cluster is unique to Roseoloviruses; however, both their function and whether they are essential for virus growth is unknown. Recently, bacterial artificial chromosome (BAC) techniques have been used to investigate HHV-6A. This study describes generation of a virus genome lacking U21-U24 (HHV-6ABACΔU21-24) and shows that infectious virus particles can be reconstituted from this BAC DNA. Our data indicate that the HHV-6 U21-U24 gene cluster is dispensable for virus propagation.

A child with acute encephalopathy associated with quadruple viral infection

Pediatric acute encephalopathy (AE) was sometimes attributed to virus infection. However, viral infection does not always result in AE. The risk factors for developing infantile AE upon virus infection remain to be determined. Here, we report an infant with AE co-infected with human herpesvirus-6 (HHV-6) and three picornaviruses, including coxsackievirus A6 (CVA6), Enterovirus D68 (EV-D68), and human parechovirus (HPeV). EV-D68 was vertically transmitted to the infant from his mother. CVA6 and HPeV were likely transmitted to the infant at the nursery school. HHV-6 might be re-activated in the patient. It remained undetermined, which pathogen played the central role in the AE pathogenesis. However, active, simultaneous infection of four viruses should have evoked the cytokine storm, leading to the pathogenesis of AE.

CONCLUSION

an infant case with active quadruple infection of potentially AE-causing viruses was seldom reported partly because systematic nucleic acid-based laboratory tests on picornaviruses were not common. We propose that simultaneous viral infection may serve as a risk factor for the development of AE.

Detection of human herpesvirus 6 in cerebrospinal fluid of children with possible encephalitis

Background:

Encephalitis is swelling and inflammation of brain, usually due to viral infection. Viral encephalitis symptoms could be fever, headache, altered level of consciousness, and seizures.

Objectives:

The aim of this study was detection of human herpesvirus-6 (HHV-6) DNA in cerebrospinal fluid (CSF) of patients with symptoms of possible acute encephalitis and without typical signs or symptoms of roseola infantum, using real-time polymerase chain reaction (PCR).

Patients and Methods:

We studied children two years old or younger, admitted to the pediatric emergency ward with encephalitis-like symptoms. Our evaluation included detection of HHV-6 in CSF of these patients. After DNA extraction, real-time PCR was performed with primers and a probe specific for the U22 open reading frame of both HHV-6A and B.

Results:

From a total of 114 patients, HHV-6 was detected in 10 (8.8%), 90% of which were boys with mean age 7.7 months and median of 7.5 months. No significant differences were found in clinical presentations and laboratory findings between the patients positive and negative for HHV-6. All the children had complete recovery without neurological deficit or death.

Conclusions:

According to this research and prevalence of HHV-6 in children, evaluation of CSF (detecting the HHV-6 DNA by PCR) is recommended in patients younger than 13 months with possible encephalitis.

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.

Rhabdomyolysis in an infant with primary human herpesvirus 6 infection

We report here the first case of rhabdomyolysis at the time of primary human herpesvirus 6 infection. The patient was a previously healthy 1-year-old girl who developed rhabdomyolysis 4 days after the onset of the primary human herpesvirus 6 infection. No other etiologic agent that might cause rhabdomyolysis was identified.

Exanthem subitum-associated encephalitis: nationwide survey in Japan

We sought to clarify clinical features of exanthem subitum associated-encephalitis/encephalopathy, generally caused by primary human herpesvirus-6 infection in Japan. A two-part questionnaire was sent to hospitals between January 2003-December 2004. Of 3357 questionnaires, 2357 (70.2%) were returned, and 2293 (68.3%) were eligible for analysis. Eighty-six cases of exanthem subitum-associated encephalitis/encephalopathy were reported. Seventy-seven (89.5%) of 86 patients were diagnosed with human herpesvirus-6 infection by virologic examination. Although 41 (50.6%) of 81 patients had no sequelae, 38 (46.9%) had neurologic sequelae. Moreover, two fatal cases (2.5%) were reported. Pleocytosis was evident in only 4 (7.5%) of 53 patients, and cerebrospinal fluid protein levels were within normal range (23.4 +/- 14.6 mg/dL S.D.) in all patients. Human herpesvirus-6 DNA was detected in 21 (53.8%) of 39 patients. Abnormal computed tomography findings were a predictor of neurologic sequelae (P = 0.0097). As a consequence of this survey, we estimate that 61.9 cases of exanthem subitum-associated encephalitis occur every year. The disease prognosis was unexpectedly poor.

Prevalence of HHV-6 integrated chromosomally among children treated for acute lymphoblastic or myeloid leukemia in the Czech Republic

Chromosomal integration of human herpesvirus 6 (HHV-6) is a novel situation found in a small percentage of individuals. While active HHV-6 infection is treatable using antivirals, the abnormally high level of HHV-6 DNA found in chromosomal integration of HHV-6 (CI-HHV-6) is not affected by such drugs. Stored DNA samples taken originally for detection of fusion genes and minimal residual disease from 339 pediatric patients treated for leukemia in the Czech Republic between the years 1995-2007 were tested retrospectively. Using real-time quantitative PCR technology, the quantity of HHV-6 DNA detected was normalized to 100,000 human genome equivalents as assessed by quantitation of the albumin gene. HHV-6 DNA was detected in 107 samples from 91 patients (26.8%). In the majority of samples (99) only a minute level of normalized viral copies (NVCs) (median 1.84 NVCs) was detected. A high viral load of approximately 100,000 NVCs was detected in 5 patients (1.5%; median 140,150 NVCs), in all of whom were confirmed subsequently CI-HHV-6 by a detection of HHV-6 DNA in hair follicles or in the nails. In all but one patient with HHV-6 variant B, variant A of the virus was detected. None of the patients with CI-HHV-6 had complications attributable to HHV-6 infection. The prevalence of CI-HHV-6 in childhood leukemia does not differ from that published for other patients or healthy populations. Where high levels of HHV-6 DNA are present, CI-HHV-6 should be confirmed as soon as possible so that potentially toxic but ineffective antiviral treatment can be stopped.

Human herpesvirus 6A (HHV-6A) and HHV-6B alter E2F1/Rb pathways and E2F1 localization and cause cell cycle arrest in infected T cells

E2F transcription factors play pivotal roles in controlling the expression of genes involved in cell viability as well as genes involved in cell death. E2F1 is an important constituent of this protein family, which thus far contains eight members. The interaction of E2F1 with its major regulator, retinoblastoma protein (Rb), has been studied extensively in the past two decades, concentrating on the role of E2F1 in transcriptional regulation and the role of Rb in cell replication and cancer formation. Additionally, the effect of viral infections on E2F1/Rb interactions has been analyzed for different viruses, concentrating on cell division, which is essential for viral replication. In the present study, we monitored E2F1-Rb interactions during human herpesvirus 6A (HHV-6A) and HHV-6B infections of SupT1 T cells. The results have shown the following dramatic alterations in E2F1-Rb pathways compared to the pathways of parallel mock-infected control cultures. (i) The E2F1 levels were elevated during viral infections. (ii) The cellular localization of E2F1 was dramatically altered, and it was found to accumulate both in the cytoplasmic and nuclear fractions, as opposed to the strict nuclear localization seen in the mock-infected cells. (iii) Although E2F1 expression was elevated, two exemplary target genes, cyclin E and MCM5, were not upregulated. (iv) The Rb protein was dephosphorylated early postinfection, a trait that also occurred with UV-inactivated virus. (v) Infection was associated with significant reduction of E2F1/Rb complexing. (vi) HHV-6 infections were accompanied by cell cycle arrest. The altered E2F1-Rb interactions and functions might contribute to the observed cell cycle arrest.

Neuroimaging of herpesvirus infections in children

Six members of the herpesvirus family cause well-described neurologic disease in children: herpes simplex virus-1 (HSV-1), herpes simplex virus-2 (HSV-2), varicella-zoster (VZV), Epstein-Barr (EBV), cytomegalovirus (CMV), and human herpes virus-6 (HHV-6). When herpesviruses infect the central nervous system (CNS), the clinical presentation is non-specific and often confounding. The clinical urgency is often underscored by progressive neurologic deficits, seizures, or even death, and prompt diagnosis and treatment rely heavily on neuroimaging. This review focuses on the spectrum of cerebral manifestations caused by these viruses, particularly on non-congenital presentations. Recent advances in our understanding of these viruses are discussed, including new polymerase chain reaction techniques that allow parallel detection, which has improved our recognition that the herpesviruses are neurotropic and involve the CNS more often than previously thought. Evolving knowledge has also better elucidated viral neuropathology, particularly the role of VZV vasculitis in the brain, HHV-6 in febrile seizures, and herpesvirus reactivation in immunosuppressed patients. The virology, clinical course, and CNS manifestations of each virus are reviewed, followed by descriptions of neuroimaging findings when these agents infect the brain. Characteristic but often subtle imaging findings are discussed, as well as technical pearls covering appropriate use of MRI and MRI adjuncts to help differentiate viral infection from mimics.

Primary human herpesvirus-6 infection in the central nervous system can cause severe disease

Human herpesvirus-6 (HHV-6) infection is common in infancy, and symptoms are usually mild. However, encephalitis and other neurologic complications have been reported. Primary HHV-6 infection has been rarely confirmed in the central nervous system. We studied 21 children with suspected HHV-6 infection, drawn from a prospective, large-scale study of neurologic infections in Finland. Human herpesvirus-6 polymerase chain reaction was performed on cerebrospinal fluid samples, and antibody tests were performed on serum and cerebrospinal fluid. We identified nine children, aged 3 to 24 months, who had HHV-6-specific nucleic acid in cerebrospinal fluid. Primary infection was confirmed by seroconversion of specific antibodies in six, whereas one had a fourfold increase, and one had a fourfold decrease, in the antibody titer supporting recent infection. Generalized and prolonged seizures appeared in six children, four had a rash, four had ataxia, and four had gastroenteritis. All but two had a high fever. At follow-up, four children had evident neurologic sequelae, ataxia, and developmental disability, and needed special education. Primary HHV-6 infection may invade the central nervous system, and can cause neurologic symptoms and potentially permanent disability in children aged <or=2 years. The possibility of HHV-6 infection must be considered when treating acutely ill children, and especially those with convulsions.

Direct detection of human herpesvirus 6 DNA in serum by the loop-mediated isothermal amplification method

BACKGROUND

A more rapid and easier method is needed for monitoring human herpesvirus 6 (HHV-6) infections. The loop-mediated isothermal amplification method (LAMP) can detect viral DNA with high specificity, efficiency, and speed under isothermal conditions. LAMP requires only simple equipment that is available in hospital laboratories.

OBJECTIVES

We evaluated LAMP as a means of detecting HHV-6 DNA directly from patients' sera.

RESULTS

The sensitivity of the HHV-6 LAMP protocol without heat denaturation was 1000 copies/tube; with heat denaturation 10 copies/tube were detected. Three hundred serum samples from children with fever were analyzed. Using HHV-6 isolation as a definition of HHV-6 infection, the sensitivity, specificity, positive predictive value, and negative predictive value of the HHV-6 LAMP method without DNA extraction were 95.5%, 95.2%, 94.0%, and 96.4%, respectively.

CONCLUSION

Direct detection of HHV-6 DNA in serum with a modified HHV-6 LAMP could be used for rapid diagnosis of exanthem subitum (ES).

[Human herpes virus type 6, etiology of an acute encephalitis in childhood: case report]

Primary infection with human herpesvirus-6 (HHV-6) causes the classical roseola infantum. Otherwise the infection is clinically silent but it may sometimes be responsible for central nervous system involvement. In order to illustrate such a type of lesions, we report on a 16-month-old girl with acute leucoencephalitis. The disease started with pyrexia 40 degrees C, followed by an episode of seizure, erythematous rash on the trunk and then coma. Brain MRI showed wide lesions on white matter. HHV-6 DNA was detected by PCR in the CSF and serum at the acute stage, and tests for HHV-6 antibody showed a significant increase of IgG antibody titre between acute and convalescent sera. One month later complete clinical recovery was observed while the MRI showed a partial disappearance of the lesions. The sero-conversion associated with the detection of the viral DNA in the serum identified a primary HHV-6 infection and the detection of viral nucleic acid in CSF gives arguments for the responsibility of the virus in the pathogenesis. When facing an acute leuco-encephalitis in infants, it is important to perform exhaustive virology investigations to rule out the implication of HHV-6 as well as other commonly incriminated pathogens (EBV, CMV, mycoplasma, enterovirus) to avoid accusing wrongly the vaccines.

Human herpesvirus 6 encephalopathy predominantly affecting the frontal lobes

Isolated cases of human herpesvirus 6 encephalopathy have recently been reported, although the pathophysiology remains largely unknown. To elucidate the changes specific to human herpesvirus 6 encephalopathy on diagnostic images, this study investigated magnetic resonance imaging findings in 10 patients with a diagnosis of human herpesvirus 6 encephalopathy including diffusion-weighted imaging in 6 of 10, and findings of cerebral blood flow imaging by single-photon emission computed tomography in 9 of 10 patients. No abnormalities were evident on T(1)-weighted, T(2)-weighted, or fluid-attenuated inversion-recovery magnetic resonance imaging during acute phases; however, diffusion-weighted imaging indicated abnormal hyperintensity in the subcortical white matter of the frontal lobes in all six patients during the acute phase. Cerebral blood flow single-photon emission computed tomography revealed decreased perfusion, predominantly in the frontal region of all nine patients during their clinical course. Disturbances predominantly affecting the frontal lobes (region) on magnetic resonance imaging and cerebral blood flow single-photon emission computed tomography were common in all patients, suggesting that the findings may be characteristic of human herpesvirus 6 encephalopathy.

Fatal HHV-6 associated encephalitis in an HIV-1 infected patient treated with cidofovir

We describe the case of a patient infected with HIV and a concomitant HHV-6 encephalitis. The patient experienced virological failure following cidofovir treatment. RT-PCR was used both for early diagnosis and follow-up.

Comparison of the SYBR Green and the hybridization probe format for real-time PCR detection of HHV-6

A comparative study was conducted of a novel real-time quantitative PCR test (LightCycler System) with FastStart DNA Master(PLUS) SYBR Green I dye to detect DNA of human herpes virus 6 (HHV-6). Results were compared with those of a real-time quantitative PCR with hybridization probe (HP) formats using the fluorescence resonance energy transfer method, and with those of a single qualitative PCR test. The detection limit of the test with SYBR Green I dye was 20 copies of the virus, similar to that of the other two tests. The reproducibility was satisfactory. The new test has the same advantages as real-time PCR with HP formats and offers a greater versatility at lower cost.

Differential tropism of human herpesvirus 6 (HHV-6) variants and induction of latency by HHV-6A in oligodendrocytes

Human herpesvirus 6 (HHV-6) is a ubiquitous β-herpesvirus associated with a number of clinical disorders. Two closely but biologically distinct variants have been described. HHV-6 variant B causes the common childhood disease exhanthem subitum, and although the pathologic characteristics for HHV-6 variant A are less well defined, HHV-6A has been suggested to be more neurotropic. We studied the effect of both HHV-6 variants in an oligodendrocyte cell line (MO3.13). Infection of M03.13 was monitored by cytopathic effect (CPE), quantitative TaqMan PCR for viral DNA in cells and supernatant, reverse transcriptase-polymerase chain reaction (RT-PCR) to detect viral RNA, and indirect immunofluorescence (IFA) to detect viral protein expression. HHV-6A infection induced significantly more CPE than infection with HHV-6B. HHV-6B induced an abortive infection associated with a decrease of the initial viral DNA load over time, early RNA expression, and no expression of viral antigen. In contrast, infection with HHV-6A DNA persisted in cells for at least 62 days. During the acute phase of infection with HHV-6A, intracellular and extracellular viral load increased and cells expressed the viral protein IE-2 and gp116/54/64. No HHV-6A RNA or protein was expressed after 30 days post infection, suggesting that HHV-6A formed a latent infection. These studies provide in vitro support to the hypothesis that HHV-6 can actively infect oligodendrocytes. Our results suggest that HHV-6A and HHV-6B have different tropism in MO3.13 cells and that an initially active HHV-6A infection can develop latency. Differences between HHV-6A and -6B infection in different neural cell types may be associated with different neurological diseases.

The natural history and laboratory diagnosis of human herpesviruses-6 and -7 infections in the immunocompetent

BACKGROUND

Human herpesviruses-6 and -7 (HHV-6/7) are widespread in all populations. In some individuals HHV-6 is found integrated into human chromosomes, which results in a high viral load in blood. HHV-6 variant B (HHV-6B) and HHV-7 primary infections, although usually silent, not infrequently cause the childhood exanthem roseola infantum and are sometimes accompanied by neurological illness. HHV-6 variant A (HHV-6A) is not associated with any disease.

OBJECTIVES

The present review focuses on the immunocompetent individual and considers the epidemiology of the two viruses and their role as human pathogens. It discusses the importance of satisfactory diagnostic tests to distinguish them, compares those currently available, and recommends how best to differentiate primary from persistent infection in each case.

RESULTS

It is explained that at the present time antibody avidity immunofluorescence tests are the most reliable discriminators of the two types of infection. In primary infection these tests can be supplemented by PCR for viral DNA in blood but careful interpretation is required for HHV-6 in view of the high persistent viral DNA load seen with chromosomal integration. Since the contribution of primary HHV-6 and -7 infections to the burden of severe neurological illness in young children is only now emerging as significant, the need to test for these viruses in such cases is stressed.

CONCLUSIONS

1. Primary HHV-6/7 infections must be distinguished from persistent infections. 2. Chromosomal integration of HHV-6 requires urgent study. 3. HHV-6A/B must be distinguished in clinical situations. 4. Where serious neurological disease/encephalitis is temporally related to immunisation it is particularly important to test for HHV-6/7 primary infection since otherwise the condition might wrongly be diagnosed as a vaccine reaction. 5. Because less is currently known about HHV-7 and HHV-6A than HHV-6B, future studies should concentrate on the former two. 6. Improvements in diagnostic tests are required for each virus.

Rapid diagnosis of human herpesvirus 6 infection by a novel DNA amplification method, loop-mediated isothermal amplification

A novel nucleic acid amplification method, termed loop-mediated isothermal amplification (LAMP), which amplifies DNA with high specificity, efficiency, and rapidity under isothermal conditions, may be a valuable tool for the rapid detection of infectious agents. LAMP was developed for human herpesvirus 6 (HHV-6), and its reliability was evaluated in this study. Although LAMP products were detected in HHV-6 B and HHV-6 A DNA, they were not detected in HHV-7 and human cytomegalovirus DNA. The sensitivity of the original HHV-6 LAMP protocol was 50 copies/tube. In order to increase the method's sensitivity, HHV-6 LAMP was modified by increasing the primer concentration. As a result of the modification, sensitivity increased to 25 copies/tube. After these initial validation studies, 13 patients with fever were tested for HHV-6 by viral isolation, serological analysis, and HHV-6 LAMP. In three of the eight patients with primary HHV-6 infection, HHV-6 DNA was detected in whole blood by the original HHV-6 LAMP protocol in not only the acute phase but also the convalescent phase. HHV-6 DNA was detected by modified HHV-6 LAMP in all eight plasma samples collected in the acute phase; however, no HHV-6 DNA was detected in plasma samples collected in the convalescent phase. Although HHV-6 DNA was detected in both the acute and convalescent phases of whole-blood samples in patients with past HHV-6 infection, it was not detected in plasma samples that did not contain latent viral DNA. Thus, detection of HHV-6 DNA in plasma by using this modified HHV-6 LAMP protocol is appropriate for diagnosis of active HHV-6 infection.

Human herpesvirus 6 (HHV6) infection

Human herpes virus-6 was first reported in 1986 and is the sixth member of the herpes virus family. HHV-6 consists of two closely related variants HHV-6A and HHV-6B. The majority of infections occur in healthy infants with most infections caused by HHV-6B. The virus preferentially infects CD4+T-lymphocytes and the surface marker CD46 acts as a co-receptor. Infection is followed by persistence and latency in different cells and organs including monocytes/macrophages, salivary glands, the brain and the kidneys. In this article we will discuss the clinical manifestations of HHV-6 infection in healthy children and the syndromes associated with HHV-6 reactivation in immunocompromised patients. Evidence of association between HHV-6 infection and different clinical entities such as multiple sclerosis, malignancy, infectious momononucleosis, drug hypersensitivity syndromes and skin eruptions is discussed. Published data on the use and efficacy of antiviral agents in complicated infections and infections in immunocompromised patients is presented.

Characterization of the immediate-early 2 protein of human herpesvirus 6, a promiscuous transcriptional activator

In the present work we report the cloning of a full-length cDNA encoding the immediate-early (IE) 2 protein from human herpesvirus 6 (HHV-6) variant A (GS strain). The transcript is 4690 nucleotides long and composed of 5 exons. Translation initiation occurs within the third exon and proceeds to the end of U86. Kinetic studies indicate that the 5.5-kb IE2 mRNA is expressed under IE condition, within 2-4 h of infection. IE2 transcripts from both variants A and B are expressed under similar kinetics with IE2 transcripts accumulating up to 96 h postinfection. Although several large transcripts (>5.5 kb) hybridized with the IE2 probe, suggesting multiple transcription initiation sites, a single form of the IE2 protein, in excess of 200 kDa, was detected by Western blot. Within cells, the IE2 protein was detected (8-48 h) as intranuclear granules while at later time points (72-120 h), the IE2 protein coalesced into a few large immunoreactive patches. Transfection of cells with an IE2 expression vector (pBK-IE2A) failed to reproduce the patch-like distribution, suggesting that other viral proteins are necessary for this process to occur. Last, IE2 was found to behave as a promiscuous transcriptional activator. Cotransfection experiments in T cells indicate that IE2 can induce the transcription of a complex promoter, such as the HIV-LTR, as well as simpler promoters, whose expression is driven by a unique set of responsive elements (CRE, NFAT, NF-kB). Moreover, minimal promoters having a single TATA box or no defined eukaryotic regulatory elements were significantly activated by IE2, suggesting that IE2 is likely to play an important role in initiating the expression of several HHV-6 genes. In all, the work presented represents the first report on the successful cloning, expression, and functional characterization of the major regulatory IE2 gene/protein of HHV-6.

Human herpesvirus-6 and -7 infections in transplantation

Human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7) are ubiquitous in the human population and cause exanthem subitum, a benign disease seen in infancy. The viruses remain latent in the body after primary infection, and reactivate in immunocompromised patients. HHV-6 infection occurs in nearly 50% of all bone marrow and in 20-30% of solid-organ transplant recipients, 2-3 weeks following the procedure. It has been suggested that the viral infection and activation result in clinical symptoms, including fever, skin rash, pneumonia, bone marrow suppression, encephalitis, and rejection. In order to understand the viral infection in greater detail, several studies investigating the route of viral transmission and diagnostic procedures have been carried out. In contrast to studies of HHV-6 infection in organ-transplant recipients, the number of studies examining HHV-7 infection in these patients is limited. According to several recent studies, HHV-7 may act as a cofactor for cytomegalovirus disease in organ-transplant recipients.

Meningitis and encephalitis in children. An update

Over the course of the past decade, much has changed on the landscape of meningitis and encephalitis in children. West Nile virus has emerged in the United States as a new etiologic pathogen causing encephalitis. Human herpesvirus-6 has been identified as a cause of encephalitis and febrile seizures. Lymphocytic choriomeningitis virus has been identified as an underrecognized neuroteratogen. The emergence of penicillin-resistant Streptococcus pneumoniae has complicated the treatment of bacterial meningitis, whereas the Haemophilus influenzae vaccine has fundamentally altered the disease's epidemiology. The recognition that much of the neuropathologic change induced by bacterial meningitis is inflammation mediated has paved the way to the demonstration that dexamethasone can substantially improve the outcome of bacterial meningitis in children. Although much progress has been made toward understanding, treating, and preventing these important infections, much remains to be learned.

Real-time PCR for quantification of human herpesvirus 6 DNA from lymph nodes and saliva

A real-time quantitative PCR assay has been developed to measure human herpesvirus 6 (HHV-6) DNA in biological specimens. The assay sensitivity was 10 copies of DNA per well, with a linear dynamic range of 10 to 10(7) copies of HHV-6 DNA. Intra- and interassay variations were, respectively, 0.88 and 0.8% for samples containing 10(2) DNA copies, 0.99 and 0.96% for samples containing 10(4) copies, and 0.76 and 0.9% for samples containing 10(6) copies. Among 34 saliva samples from healthy subjects, 26 were found to contain HHV-6 DNA (76.5%; median, 23,870 copies/ml), and following a single freeze-thaw cycle, 25 of the same samples were found to be positive for HHV-6 DNA, although at a statistically significantly lower concentration (median, 3,497 copies/ml). The assay enabled detection of HHV-6 DNA in lymph node biopsies from patients with Hodgkin's disease (HD) (13 of 37 patients [35.1%]), B-cell neoplasms (8 of 36 patients [22.2%]), and T- or NK-cell neoplasms (3 of 13 patients [23.1%]), with concentrations ranging from 100 to 864,640 HHV-6 copies per microg of DNA (HHV-6B being found in every case except two). All HD patients infected with HHV-6 presented clinically with the nodular sclerosis subtype of HD. The real-time quantitative PCR assay developed here was simple to perform and was sensitive over a wide range of HHV-6 concentrations. It therefore appears to be of potential value in clinical investigation or diagnosis of HHV-6 infection.