Human herpesvirus 6 encephalitis

Inherited IRAK-4 Deficiency in Acute Human Herpesvirus-6 Encephalitis

Human herpesvirus-6 (HHV-6) infection can rarely cause life-threatening conditions, such as encephalitis, in otherwise healthy children, with unclear pathogenesis. We studied a child who presented with acute HHV-6 encephalitis at the age of 10 months and who was homozygous for a novel missense mutation in IRAK4, encoding interleukin-1 receptor-associated kinase 4, identified by whole-exome sequencing. We tested the damaging impact of this mutation in silico by molecular dynamics simulations and in vitro by biochemical and functional experiments utilizing cell lines and patient's cells. We found that the mutation is severely hypomorphic, impairing both the expression and function of IRAK-4. Patient's leukocytes had barely detectable levels of IRAK-4 and diminished anti-viral immune responses to various stimuli inducing different Toll-like receptors and cytosolic nucleic acid sensors. Overall, these findings suggest that acute HHV-6 encephalitis can result from inborn errors of immunity to virus. This study represents the first report of isolated acute HHV-6 infection causing encephalitis in an inherited primary immunodeficiency, notably autosomal recessive (AR) partial IRAK-4 deficiency, and the first report of AR IRAK-4 deficiency presenting with a severe viral disease, notably HHV-6 encephalitis upon an acute infection, thereby expanding the clinical spectrum of IRAK-4 deficiency.

Murine roseolovirus does not accelerate amyloid-β pathology and human roseoloviruses are not over-represented in Alzheimer disease brains

BACKGROUND

The role of viral infection in Alzheimer Disease (AD) pathogenesis is an area of great interest in recent years. Several studies have suggested an association between the human roseoloviruses, HHV-6 and HHV-7, and AD. Amyloid-β (Aβ) plaques are a hallmark neuropathological finding of AD and were recently proposed to have an antimicrobial function in response to infection. Identifying a causative and mechanistic role of human roseoloviruses in AD has been confounded by limitations in performing in vivo studies. Recent -omics based approaches have demonstrated conflicting associations between human roseoloviruses and AD. Murine roseolovirus (MRV) is a natural murine pathogen that is highly-related to the human roseoloviruses, providing an opportunity to perform well-controlled studies of the impact of roseolovirus on Aβ deposition.

METHODS

We utilized the 5XFAD mouse model to test whether MRV induces Aβ deposition in vivo. We also evaluated viral load and neuropathogenesis of MRV infection. To evaluate Aβ interaction with MRV, we performed electron microscopy. RNA-sequencing of a cohort of AD brains compared to control was used to investigate the association between human roseolovirus and AD.

RESULTS

We found that 5XFAD mice were susceptible to MRV infection and developed neuroinflammation. Moreover, we demonstrated that Aβ interacts with viral particles in vitro and, subsequent to this interaction, can disrupt infection. Despite this, neither peripheral nor brain infection with MRV increased or accelerated Aβ plaque formation. Moreover, -omics based approaches have demonstrated conflicting associations between human roseoloviruses and AD. Our RNA-sequencing analysis of a cohort of AD brains compared to controls did not show an association between roseolovirus infection and AD.

CONCLUSION

Although MRV does infect the brain and cause transient neuroinflammation, our data do not support a role for murine or human roseoloviruses in the development of Aβ plaque formation and AD.

Suspected Post-ictal Psychosis in Temporal Lobe Epilepsy Secondary to Human Herpesvirus 6 Encephalitis

Human herpesvirus 6 (HHV-6) may lead to temporal lobe epilepsy (TLE). Psychotic syndrome frequency in the setting of TLE is 7% to 11%. We report a case of post-ictal psychosis (PIP) secondary to TLE in the setting of HHV-6 encephalitis. A 58-year-old male presented with a two-day history of severe confusion, personality changes, and new-onset psychosis. Lumbar puncture was positive for HHV-6. Electroencephalogram (EEG) revealed left temporal sharp waves during drowsiness and sleep, suggestive of focal epileptiform discharges without clinical seizures. Valproate and olanzapine were employed for epilepsy and agitation. Psychosis and confusion resolved with subsequent discharge. Out of the other diagnoses, PIP in the setting of TLE secondary to HHV-6 given the clinical response to acyclovir. While HHV-6 encephalitis may cause TLE, this patient did not have a history of seizures and EEG did not capture active seizures. It is unclear if the sharp waves were incidental or indicative of TLE. Additionally, PIP is seen more commonly with left-sided EEG changes. Low-dose olanzapine was efficacious in resolving symptoms, which is typical in PIP. Both HHV-6 encephalitis and TLE have the potential to cause memory impairments and personality changes, which were seen in this patient. Patients with both TLE and PIP are less likely to exhibit focal ictal discharges than those with only TLE, which may explain the absence of active seizure activity on EEG.

Human herpesvirus 6A U27 plays an essential role for the virus propagation

Human herpesvirus 6A (HHV-6A) is a member of the genus Roseolovirus and the subfamily Betaherpesvirinae. It is similar to and human cytomegalovirus (HCMV). HHV-6A encodes a 41 kDa nuclear phosphoprotein, U27, which acts as a processivity factor in the replication of the viral DNA. HHV-6A U27 has 43% amino acid sequence homology with HCMV UL44, which is important for DNA replication. A previous study on HHV-6A U27 revealed that it greatly increases the in vitro DNA synthesis activity of HHV-6A DNA polymerase. However, the role of U27 during the HHV-6A virus replication process remains unclear. In this study, we constructed a U27-deficient HHV-6A mutant (HHV-6ABACU27mut) with a frameshift insertion at the U27 gene using an HHV-6A bacterial artificial chromosome (BAC) system. Viral reconstitution from the mutant BAC DNA was not detected, in contrast to the wild type and the revertant from the U27 mutant. This suggests that U27 plays a critical role in the life cycle of HHV-6A.

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

Objective

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

Background

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

Design/Methods

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

Results

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

Interpretation

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

HHV-6 Infection in an Immunocompetent Patient with Multi-organ Failure

Human herpesvirus 6 (HHV-6) is a double-stranded DNA virus part of the Herpesviridae family that colonizes nearly 100% of the human population. The virus is known to be the etiologic agent of roseola infantum, a self-limited disease in childhood and reactivation of the virus later in life is linked to potentially severe manifestations, including encephalitis, in immunosuppressed patients. It is rare in immunocompetent patients, but there have been several reports of encephalitis due to HHV-6 reactivation. We describe here a case of altered mental status and multi-organ failure in an immunocompetent woman, whose cerebrospinal fluid (CSF) was positive for HHV-6 DNA by polymerase chain reaction (PCR).

Neurologic complications of transplantation

Major neurologic morbidity, such as seizures and encephalopathy, complicates 20-30% of organ and stem cell transplantation procedures. The majority of these disorders occur in the early posttransplant period, but recipients remain at risk for opportunistic infections and other nervous system disorders for many years. These long-term risks may be increasing as acute survival increases, and a greater number of "sicker" patients are exposed to long-term immunosuppression. Drug neurotoxicity accounts for a significant proportion of complications, with posterior reversible leukoencephalopathy syndrome, primarily associated with calcineurin inhibitors (i.e., cyclosporine and tacrolimus), being prominent as a cause of seizures and neurologic deficits. A thorough evaluation of any patient who develops neurologic symptoms after transplantation is mandatory, since reversible and treatable conditions could be found, and important prognostic information can be obtained.

Rapid chain generation of interpostsynaptic functional LINKs can trigger seizure generation: Evidence for potential interconnections from pathology to behavior

The experimental finding that a paroxysmal depolarizing shift (PDS), an electrophysiological correlate of seizure activity, is a giant excitatory postsynaptic potential (EPSP) necessitates a mechanism for spatially summating several EPSPs at the level of the postsynaptic terminals (dendritic spines). In this context, we will examine reversible interpostsynaptic functional LINKs (IPLs), a proposed mechanism for inducing first-person virtual internal sensations of higher brain functions concurrent with triggering behavioral motor activity for possible pathological changes that may contribute to seizures. Pathological conditions can trigger a rapid chain generation and propagation of different forms of IPLs leading to seizure generation. A large number of observations made at different levels during both ictal and interictal periods are explained by this mechanism, including the tonic and clonic motor activity, different types of hallucinations, loss of consciousness, gradual worsening of cognitive abilities, a relationship with kindling (which uses an augmented stimulation protocol than that used for inducing long-term potentiation (LTP), which is an electrophysiological correlate of behavioral makers of internal sensation of memory), effect of a ketogenic diet on seizure prevention, dendritic spine loss in seizure disorders, neurodegenerative changes, and associated behavioral changes. The interconnectable nature of these findings is explained as loss of function states of a proposed normal functioning of the nervous system.

Human herpesvirus 6 U11 protein is critical for virus infection

All herpesviruses contain a tegument layer comprising a protein matrix; these proteins play key roles during viral assembly and egress. Here, liquid chromatography and tandem mass spectrometry analysis (LC-MS/MS) of proteins from human herpesvirus 6 (HHV-6)-infected cells revealed a possible association between two major tegument proteins, U14 and U11. This association was verified by immunoprecipitation experiments. Moreover, U11 protein was expressed during the late phase of infection and incorporated into virions. Finally, in contrast to its revertant, a U11 deletion mutant could not be reconstituted. Taken together, these results suggest that HHV-6 U11 is an essential gene for virus growth and propagation.

Central nervous system infections in cancer patients and hematopoietic stem cell transplant recipients

Central nervous system (CNS) infections in cancer patients present a diagnostic and therapeutic challenge for clinicians. While CNS infections are not frequent complications of cancer, its therapies, or hematopoietic stem cell transplantation, the importance of CNS infections lies in their propensity to result in profound morbidity and substantial mortality in this vulnerable patient population. With an expanding population of patients with malignant disease undergoing more potent and aggressive therapies and with the advent of newer immunomodulatory agents, the incidence of CNS infectious complications is likely to rise. This chapter will summarize the clinical and diagnostic evaluation of potential infections of the CNS in these patients and will discuss particular pathogens of interest with regard to this at-risk patient population.

Associations between human herpesvirus-6, human papillomavirus and cervical cancer

Cervical cancer (CxCa) is the second most common cancer among women globally. Human papillomavirus (HPV) infection is thought to be a necessary, but not sufficient, causal factor in CxCa development. Why some women are able to clear HPV infection with no adverse effects, whereas others develop cancer, remains unclear. HHV-6 has demonstrated transformative abilities and has been shown to be present in the genital tract. However, based on the current evidence, we cannot conclude that HHV-6 is a co-factor in HPV-associated carcinogenesis. Nonetheless, future research is warranted because of several crucial gaps in the literature.

Novel marmoset (Callithrix jacchus) model of human Herpesvirus 6A and 6B infections: immunologic, virologic and radiologic characterization

Human Herpesvirus 6 (HHV-6) is a ubiquitous virus with an estimated seroprevalence of 95% in the adult population. HHV-6 is associated with several neurologic disorders, including multiple sclerosis, an inflammatory demyelinating disease affecting the CNS. Animal models of HHV-6 infection would help clarify its role in human disease but have been slow to develop because rodents lack CD46, the receptor for cellular entry. Therefore, we investigated the effects of HHV-6 infections in a non-human primate, the common marmoset Callithrix jacchus. We inoculated a total of 12 marmosets with HHV-6A and HHV-6B intravenously and HHV-6A intranasally. Animals were monitored for 25 weeks post-inoculation clinically, immunologically and by MRI. Marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms and generated virus-specific antibody responses, while those inoculated intravenously with HHV-6B were asymptomatic and generated comparatively lower antibody responses. Viral DNA was detected at a low frequency in paraffin-embedded CNS tissue of a subset of marmosets inoculated with HHV-6A and HHV-6B intravenously. When different routes of HHV-6A inoculation were compared, intravenous inoculation resulted in virus-specific antibody responses and infrequent detection of viral DNA in the periphery, while intranasal inoculation resulted in negligible virus-specific antibody responses and frequent detection of viral DNA in the periphery. Moreover, marmosets inoculated with HHV-6A intravenously exhibited neurologic symptoms, while marmosets inoculated with HHV-6A intranasally were asymptomatic. We demonstrate that a marmoset model of HHV-6 infection can serve to further define the contribution of this ubiquitous virus to human neurologic disorders.

Chromosomally-integrated human herpesvirus 6 in familial glioma etiology

Human herpesvirus 6 (HHV-6) is a highly neurotropic beta-herpesvirus with demonstrated transformative properties. HHV-6 infection has been implicated in the etiologies of cancers, including lymphoma and leukemia; conditions with brain involvement, including epilepsy and encephalitis; and other disorders. HHV-6 is also the only human herpesvirus that has been proven to integrate into the chromosomes of a proportion (1-12%) of infected individuals. Because several traditional genetic association studies have failed to identify a variant that can account for the established relationship between family history and glioma risk, the possibility that chromosomally-integrated HHV-6 (CI-HHV-6), as a heritable factor, may explain a proportion of familial glioma cases warrants evaluation. To test this hypothesis, the prevalence of CI-HHV-6 in familial glioma cases and related and unrelated cancer-free control groups should be compared. Among glioma-affected families, the inheritance pattern of CI-HHV-6 could be evaluated by constructing pedigrees. If CI-HHV-6 is found to be associated with familial glioma risk, this knowledge could potentially lead to the future development of novel therapeutic and preventive approaches, including vaccines and immunotherapies targeted at the HHV-6 sequences.

Cord-blood hematopoietic stem cell transplant confers an increased risk for human herpesvirus-6-associated acute limbic encephalitis: a cohort analysis

Human herpesvirus-6 (HHV-6) frequently reactivates after allogeneic hematopoietic stem cell transplantation (HSCT); its most severe manifestation is the syndrome of posttransplantation acute limbic encephalitis (HHV-6-PALE). The epidemiology, risk factors, and characteristics of HHV-6-PALE after unrelated cord-blood transplantation (UCBT) are not well characterized. We analyzed 1344 patients undergoing allogeneic HSCT between March 2003 and March 2010 to identify risk factors and characteristics of HHV-6-PALE. The cohort included 1243 adult-donor HSCT and 101 UCBT recipients. All patients diagnosed with HHV-6-PALE had HHV-6 DNA in cerebrospinal fluid (CSF) specimens in addition to symptoms and studies indicating limbic encephalitis. Nineteen cases (1.4%) of HHV-6-PALE were identified during this study: 10 after UCBT (9.9%) and 9 after adult-donor HSCT (0.7%), for an incidence rate of 1.2 cases/1000 patient-days compared to 0.08 cases/1000 patient-days (P < .001), respectively. Risk factors for HHV-6-PALE on multivariable Cox modeling were UCBT (adjusted hazard ratio [aHR], 20.0; 95% confidence interval [CI], 7.3-55.0; P < .001), time-dependent acute graft-versus-host disease (aGVHD) grades II to IV (aHR, 7.5; 95% CI, 2.8-19.8; P < .001), and adult-mismatched donor (aHR, 4.3; 95% CI, 1.1-17.3; P = .04). Death from HHV-6-PALE occurred in 50% of affected patients undergoing UCBT and no recipients of adult-donor cells. Patients receiving UCBT have increased risk for HHV-6-PALE and greater morbidity from this disease.

Visceral involvements and long-term sequelae in drug-induced hypersensitivity syndrome

Drug-induced hypersensitivity syndrome (DIHS) is a severe systemic reaction with several herpesvirus reactivations. Multiple organ failures appear during the course of the disease. The severity of DIHS is determined by the degree of visceral involvement. Autoimmune diseases also develop several months to years after the apparent clinical resolution of DIHS.

Metagenomics for the discovery of novel human viruses

Modern laboratory techniques for the detection of novel human viruses are greatly needed as physicians and epidemiologists increasingly deal with infectious diseases caused by new or previously unrecognized pathogens. There are many clinical syndromes in which viruses are suspected to play a role, but for which traditional microbiology techniques routinely fail in uncovering the etiologic agent. In addition, new viruses continue to challenge the human population owing to the encroachment of human settlements into animal and livestock habitats, globalization, climate change, growing numbers of immunocompromised people and bioterrorism. Metagenomics-based tools, such as microarrays and high-throughput sequencing are ideal for responding to these challenges. Pan-viral microarrays, containing representative sequences from all known viruses, have been used to detect novel and distantly-related variants of known viruses. Sequencing-based methods have also been successfully employed to detect novel viruses and have the potential to detect the full spectrum of viruses, including those present in low numbers.

Clinical and imaging findings suggesting human herpesvirus 6 encephalitis

We sought to distinguish patients testing positive for human herpesvirus 6 from those testing negative, based on clinical features and magnetic resonance images. Sixteen immunosuppresed patients were tested by polymerase chain reaction for human herpes virus 6 DNA in cerebrospinal fluid (nine positive results). Medical records were examined for agitation, altered mental status, hallucinations, insomnia, memory loss, and seizures. Patients were sorted by viral status. Clinical features were compared with imaging findings. Insomnia, agitation, and hallucinations were preferentially evident in human herpes virus 6-positive patients. Imaging abnormalities were evident in the hippocampus of both groups. However, extrahippocampal involvement was more common in human herpes virus 6-positive patients and among those with insomnia and hallucinations or seizures. Patients with memory loss and imaging abnormalities in the entorhinal cortex or amygdala were likely to test positive, as were patients with hallucinations and abnormal magnetic resonance signal in the hippocampus. Human herpes virus 6 encephalitis patients present with diverse clinical features that are also common among patients who test negative. This entity should be suspected in patients who present with insomnia, seizures, or hallucinations when imaging abnormalities are evident in the hippocampus, amygdala, and limbic structures beyond the medial temporal lobe.

Detection of human herpesvirus-6 in adult central nervous system tumors: predominance of early and late viral antigens in glial tumors

The purpose is to determine the incidence of active and latent human herpesvirus-6 (HHV-6) infection in a large cohort of adult primary and recurrent CNS tumors. We screened a tissue microarray (TMA) containing more than 200 adult primary and recurrent CNS tumors with known clinical information for the presence of HHV-6 DNA by in situ hybridization (ISH) and protein by immunohistochemistry (IHC). One hundred six of 224 (47%) CNS tumors were positive for HHV-6 U57 Major Capsid Protein (MCP) gene by ISH compared to 0/25 non tumor control brain (P = 0.001). Fourteen of 30 (47%) tumors were HHV-6 MCP positive by nested PCR compared to 0/25 non-tumor brain controls (P = 0.001), revealing HHV-6 Variant A in 6 of 14 samples. HHV-6A/B early (p41) and late (gp116/64/54) antigens were detected by IHC in 66 of 277 (24%) (P = 0.003) and 84 of 282 (35%) (P = 0.002) tumors, respectively, suggesting active infection. HHV-6 p41 (P = 0.645) and gp116/64/54 (P = 0.198) antigen detection was independent of recurrent disease. Glial tumors were 3 times more positive by IHC compared to non glial tumors for both HHV-6 gp116/64/54 (P = 0.0002) and HHV-6 p41 (P = 0.004). Kaplan Meier survival analysis showed no effect of HHV-6 gp116/64/54 (P = 0.852) or HHV-6 p41 (P = 0.817) antigen detection on survival. HHV-6 early and late antigens are detected in adult primary and recurrent CNS tumors more frequently in glial tumors. We hypothesize that the glial-tropic features of HHV-6 may play an important modifying role in tumor biology that warrants further investigation.