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An increased awareness of diseases associated with Human herpesvirus 6 (HHV-6) infection or reactivation has resulted in a growing interest in the evaluation of the best treatment options available for the clinical management of HHV-6 disease. However, no compound has yet been approved exclusively for HHV-6 infection treatment. For this reason, the identification of anti-HHV6 compounds provides a valuable opportunity for developing efficient antiviral therapies. A possible target for antiviral drugs is the virus-cell fusion step. In this study, we synthetized potential fusion intermediates inhibitors based on the rhodanine structure. The obtained derivatives were tested for cytotoxicity and for antiviral activity in human cells infected with HHV6. Level of infection was monitored by viral DNA quantification at different time points up to 7 days post infection. Among the synthetized derivatives, 9e showed a significative inhibitory effect on viral replication that lasted over 7 days, probably attributable to the particular combination of hydrophilic and hydrophobic substituents to the rhodanine moiety. Our results support the use of these amphipathic fusion inhibitors for the treatment of HHV-6 infections., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Human herpesvirus 6 (HHV-6A and HHV-6B) can cause primary infection or reactivate from latency in liver transplant recipients, which can result in a variety of clinical syndromes, including fever, hepatitis, encephalitis and higher rates of graft dysfunction as well as indirect effects including increased risks of mortality, CMV disease, hepatitis C progression and greater fibrosis scores. Although HHV-6 infection is currently diagnosed by quantifying viral DNA in plasma or blood, biopsy to demonstrate histopathological effects of HHV-6 remains the gold standard for diagnosis of end-organ disease. HHV-6 reactivation may be restricted to the infected organ with no evidence of active infection in the blood. HHV-6 infections in liver transplant patients are mostly asymptomatic, but clinically significant tissue-invasive infections have been treated successfully with ganciclovir, foscarnet or cidofovir. Inherited chromosomally integrated HHV-6 (ciHHV-6), in either the recipient or the donor organ, may create confusion about systemic HHV-6 infection. Recipients with inherited ciHHV-6 may have an increased risk of opportunistic infection and graft rejection. This article reviews the current scientific data on the clinical effects, risk factors, pathogenesis, diagnosis and treatment of HHV-6 infections in liver transplant recipients., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Human herpesvirus (HHV)-6 reactivation is associated with severe forms of encephalitis among patients undergoing hematopoietic stem cell transplantation. Cases in non-neutropenic patients are uncommon. The efficacy of ganciclovir and other compounds that are used for the treatment of HHV-6 encephalitis remains suboptimal and linked to toxicity. Valganciclovir, the oral prodrug of ganciclovir, could be practical to treat outpatients, but it is not commonly used for severe cases. We report a case of HHV-6 encephalitis in a non-neutropenic patient successfully treated with valganciclovir and undergoing therapeutic drug monitoring in plasma and in the cerebrospinal fluid. Resolution of infectious foci was documented by cerebral MRI and F18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). A review of the literature on HHV-6 encephalitis is also reported.

Human herpes virus-6 (HHV-6) reactivation is a well-recognised complication following haematological stem cell transplantation, but it is novel in the context of combination immunomodulatory therapy for autoimmune disease. We report a case of severe anterograde amnesia caused by HHV-6 encephalitis in a young female patient on rituximab, azathioprine and prednisolone for dermatomyositis (DM). The use of targeted biologic treatments for systemic autoimmune connective tissue diseases (CTDs) is increasing, particularly when refractory to conventional management. The anti-CD20 B cell depleting monoclonal antibody, rituximab is now increasingly used, often in combination with conventional immunomodulatory treatments, in certain autoimmune neurological conditions and systemic CTDs including DM. Physicians should be aware of the possibility of HHV-6 in those who develop encephalitis while CD20 B cell deplete, especially in the presence of additional immunomodulatory therapies. Prompt diagnosis and treatment of HHV-6 encephalitis with evidence-based anti-viral therapy may help reduce the extent of irreversible morbidity such as amnesia.

We describe successful treatment of 3 cases of human herpesvirus 6 (HHV-6) encephalitis/myelitis following cord blood transplantation (CBT). Ganciclovir (GCV) (10 mg/kg/day) reduced HHV-6 load to undetectable levels in cerebrospinal fluid (CSF). Early dose reduction in the presence of HHV-6 detectable in CSF resulted in an increased HHV-6 load. GCV was capably shifted to valganciclovir (VGCV) with an almost equivalent concentration. GCV/VGCV may be effective for HHV-6 encephalitis/myelitis after CBT, although HHV-6 load in CSF should be monitored., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Human roseoloviruses include three different species, human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, HHV-7), genetically related to human cytomegalovirus. They exhibit a wide cell tropism in vivo and, like other herpesviruses, induce a lifelong latent infection in humans. In about 1% of the general population, HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6). Many active infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. They also may cause serious diseases, particularly in immunocompromised individuals, including hematopoietic stem-cell transplant (HSCT) and solid-organ transplant recipients, and acquired immunodeficiency syndrome (AIDS) patients. This opportunistic pathogenic role is formally established for HHV-6 infection and less clear for HHV-7. It mainly concerns the central-nervous system, bone marrow, lungs, gastrointestinal tract, skin, and liver. As the best example, HHV-6 causes both exanthema subitum, a benign disease associated with primary infection, and severe encephalitis associated with virus reactivations in HSCT recipients. Diagnosis using serologic and direct antigen-detection methods currently exhibits limitations. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time polymerase-chain reaction (PCR). The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active infections, but there is currently no consensus regarding the indications of treatment or specifics of drug administration. Numerous questions about HHV-6A, HHV-6B, HHV-7 are still pending, concerning in particular clinical impact and therapeutic options in immunocompromised patients.

Background: Human herpesvirus (HHV)6 positivity in the context of drug hypersensitivity syndrome (DHS) may influence disease severity. Systemic corticosteroid treatment of those with DHS testing positive for HHV6 has been speculated to prolong the duration of disease., Objectives: To evaluate whether paediatric HHV6-positive patients with DHS develop a more severe illness than those without presumed reactivation, and to evaluate the response to systemic corticosteroid treatment., Methods: A retrospective case series of 29 paediatric inpatients treated for DHS and tested for HHV6 was undertaken. HHV6-positive and -negative patients were identified and stratified into groups treated or not treated with systemic corticosteroids to examine their disease severity on the basis of hospital length of stay (LOS), total number of febrile days (Tfeb) and days until cessation of progression (CTP)., Results: Human herpesvirus6-positive patients had similar demographic characteristics to those of HHV6-negative patients, but had significantly longer hospital LOS (11·5 days vs. 5 days, P = 0·039), Tfeb (12·5 days vs. 3 days, P = 0·032) and CTP (4 days vs. 2 days, P = 0·014). All HHV6-positive patients and most (80%) of the HHV6-negative patients received systemic corticosteroids. Among the HHV6-negative patients, those who received corticosteroids showed significantly shorter CTP than those who did not (3 days vs. 2 days, P = 0·043). Additionally, there was a trend towards shorter hospital LOS and Tfeb among HHV6-negative patients who received corticosteroids vs. those who did not, although these differences were not statistically significant. The most common inciting drugs included trimethoprim-sulfamethoxazole (34%), phenytoin (10%) and amoxicillin (10%)., Conclusions: Human herpesvirus6 positivity with DHS is associated with a more severe disease course. Treatment with systemic corticosteroids was associated with a trend towards reduced hospital LOS and Tfeb, and a significantly reduced number of days until cessation of progression., (© 2014 British Association of Dermatologists.)

Human herpesvirus 6 (HHV-6) infections are typically mild and in rare cases can result in encephalitis. A common theme among all the herpesviruses, however, is the reactivation upon immune suppression. HHV-6 commonly reactivates in transplant recipients. No therapies are approved currently for the treatment of these infections, although small studies and individual case reports have reported intermittent success with drugs such as cidofovir, ganciclovir, and foscarnet. In addition to the current experimental therapies, many other compounds have been reported to inhibit HHV-6 in cell culture with varying degrees of efficacy. Recent advances in the development of new small molecule inhibitors of HHV-6 will be reviewed with regard to their efficacy and spectrum of antiviral activity. The potential for new therapies for HHV-6 infections will also be discussed, and they will likely arise from efforts to develop broad spectrum antiviral therapies for DNA viruses., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Background: Human herpesvirus 6 (HHV-6) is an important cause of fulminant or acute viral myocarditis. However, insufficiency of standard antiviral treatment against HHV-6 is an emerging problem., Objectives: To describe the case of child with HHV-6 myocarditis who was treated by unloading with a left ventricular assist device and Artesunate., Study Design: Case report supported by histological and viral diagnoses via a combination of histology/immunohistochemistry and polymerase chain reaction techniques performed on cardiac tissues before and after treatment., Results: Following therapeutic intervention, the clinical status and heart function improved. Endomyocardial biopsies revealed decreased levels of HHV-6B DNA in the myocardium and the disappearance of histological findings in support of lymphocytic myocarditis. Left ventricular assist device could be explanted. No adverse effects of Artesunate were noted., Conclusions: In addition to existing heart failure treatments, Artesunate can be considered as an effective candidate for clinical use in cases of HHV-6B associated myocarditis., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Severe hyponatremia is a critical electrolyte abnormality in allogeneic stem cell transplantation (allo-SCT) recipients and >50% of cases of severe hyponatremia are caused by the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Here, we present a patient with rapidly progressive severe hyponatremia as an initial sign and symptom of human herpesvirus-6-associated post-transplantation acute limbic encephalitis (HHV-6 PALE) after allo-SCT. A 45-year-old woman with acute lymphoblastic leukemia received unrelated bone marrow transplantation from a one locus-mismatched donor at the DR locus. On day 21, she developed a generalized seizure and loss of consciousness with severe hyponatremia, elevated serum antidiuretic hormone (ADH), and decreased serum osmolality. A high titer of HHV-6 DNA was detected in cerebrospinal fluid. Treatment with foscarnet sodium and hypertonic saline was started with improvement of neurological condition within several days. Although an elevated serum ADH, low serum osmolality, and high urinary osmolality persisted for 2 months, she had no other recurrent symptoms of encephalitis. Our experience suggests that hyponatremia accompanied by SIADH should be recognized as a prodromal or concomitant manifestation of HHV-6 PALE, and close monitoring of serum sodium levels in high-risk patients for HHV-6 PALE is necessary for immediate diagnosis and treatment initiation., (© 2012 John Wiley & Sons A/S.)

Background: There have been no reports of human herpesvirus-6 (HHV-6) encephalitis treatment based on both HHV-6 DNA load and the antiviral agent's concentration in the cerebrospinal fluid (CSF)., Patient: A 20-year-old male with a hematological malignancy developed HHV-6 encephalitis 15 days after unrelated cord blood transplantation (UCBT). He had fever, chest pain, memory impairment, and insomnia. His CSF showed no increased cell counts, but the amount of HHV-6 DNA was elevated to 2.0 × 10(6) copies/ìgDNA. Magnetic resonance imaging (MRI) of the head revealed abnormal high-intensity signals in the left limbic system on T2-weighted and diffusion-weighted images. Intravenous administration of ganciclovir (GCV) was initiated at 5 mg/kg every 12 h on day 18, and was continued until day 137. The amount of HHV-6 DNA in the plasma became undetectable on day 25. The HHV-6 load in the CSF decreased to 1.5 × 10(3) copies/ìgDNA on day 32, and reached undetectable levels on day 53. The mean concentration of GCV 1 h after an infusion of 5 mg/kg was 4.12 mg/mL in plasma and 0.7 mg/mL in CSF. The chest pain and insomnia disappeared on days 35 and 47, respectively. Memory defects recovered up to day 85., Conclusion: Serial quantification of HHV-6 DNA in CSF may be useful for successful treatment with GCV in post-transplant HHV-6 encephalitis.

High incidences of human herpesvirus (HHV)-6 encephalitis have recently been reported from several Japanese SCT centers. To evaluate the effect of low-dose foscarnet (PFA) in preventing HHV-6 infection among recipients of unrelated BM or cord blood (CB), we examined consecutive cohorts without prophylaxis against HHV-6 (cohort 1, n=51) and with PFA prophylaxis (cohort 2, PFA 50 mg/kg/day for 10 days after engraftment, n=67). Plasma real-time PCR assay was performed weekly. High-level reactivation defined as HHV-6 DNA > or =10(4) copies/mL by day 70 was the primary endpoint. No significant reduction of high-level reactivation was seen in cohort 2 (19.4%) compared with cohort 1 (33.8%, P=0.095). A trend was identified toward fewer high-level HHV-6 reactivations in cohort 2 among recipients of unrelated BM (P=0.067), but no difference in incidence was observed among CB recipients (P=0.75). Breakthrough HHV-6 encephalitis occurred following PFA prophylaxis in three patients, and incidence of HHV-6 encephalitis did not differ between cohort 1 (9.9%) and cohort 2 (4.5%, P=0.24). In conclusion, 50 mg/kg/day of PFA does not effectively suppress HHV-6 reactivation and cannot prevent all cases of HHV-6 encephalitis. To effectively prevent HHV-6 encephalitis, alternative approaches based on the pathogenesis of HHV-6 encephalitis will probably be required.

Background: Human herpesvirus 6 (HHV-6) is a neurotropic virus implicated in central nervous system (CNS) dysfunction, multiple sclerosis, seizures and encephalitis. Inherited or "chromosomally integrated" HHV-6 (CIHHV-6) is a condition characterized by high DNA loads and germ line transmission of HHV-6 genomes, which are integrated into the telomere., Objectives: We previously reported that integrated HHV-6 can be reactivated by trichostatin A in vitro. Therefore, we hypothesized that a broad array of neurological symptoms of CIHHV-6 patients may respond to antiviral drug treatment., Study Design: The patients have been treated with antiviral drugs and monitored for viral load, late mRNA, and clinical improvement., Results: Antiviral therapy of two CIHHV patients resulted in successful clinical resolution. However, both patients relapsed on multiple occasions within 4-6 months of cessation of antiviral therapy., Conclusions: Successful antiviral drug treatment suggests that clinical symptoms of these patients were due to symptomatic reactivation of CIHHV-6. Alternatively, some CIHHV-6 patients may have a reduced resistance to community-acquired HHV-6 strains due to tolerance leading to persistent infections., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Human herpesvirus 6 (HHV-6) is a ubiquitous virus inducing a life-long latent infection of its human host. Acute infections (AIs) have been recognized as the cause of severe diseases. These AIs correspond to primary infections (PIs), mainly occurring in young children, endogenous reactivations (ENRs), observed at any age, and putative exogenous reinfections (EXRs). The diagnosis of AIs is now essentially based on the quantification of viral load in bodily fluids and organs by means of real time PCR. However, this diagnosis is currently bothered by the lack of well established viral load thresholds for the different levels of virus replication, the concomitant infection with the two variants HHV-6A and HHV-6B, and the existence, albeit at low frequency, of chromosomal integration of viral DNA. An additional challenge is the difficulty to establish the causality relationship between AI and disease. Although many AIs are asymptomatic or poorly symptomatic with a spontaneous favourable outcome, some have been credited with serious clinical manifestations affecting central nervous system, liver, gastrointestinal tract, lungs, and bone marrow. The main favouring factor for such serious diseases is cellular immune deficiency. These severe diseases can be exemplified by encephalitis cases either associated with PI in young children or with ENR, especially in haematopoietic stem cell transplant recipients. The antiviral drugs ganciclovir, foscarnet and cidofovir have proven to be efficient against AIs and related diseases but the indications and conditions of their use are not yet formally approved. This emphasizes the need for controlled studies addressing both the clinical impact and therapy of HHV-6 AIs., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Human herpesvirus 6 (HHV-6) is frequently detected after allogeneic hematopoietic cell transplantation (allo-HCT); however, the clinical interpretation of HHV-6 viremia in a transplant patient is challenging as it may signify asymptomatic reactivation, chromosomal integration of the virus genome in the donor or recipient with no clinical significance, or severe HHV-6 disease. Here we present a case of HHV-6 disease after allo-HCT presenting as pure red cell aplasia, secondary graft failure, and severe immunosuppression causing multiple severe bacterial super-infections. Examination of pre-transplant patient and donor samples as well as serial determination of HHV-6 DNA copy numbers after transplantation were necessary to definitively interpret HHV-6 viremia as active HHV-6 infection with a causative role in pancytopenia and immune suppression. Foscarnet treatment resulted both in viral load decline and disappearance of HHV-6-related bone marrow suppression and predisposition to severe infections. Clinicians should be aware of the wide array of clinical manifestations and the diagnostic pitfalls of post-transplant HHV-6 disease. These issues are extremely challenging, as they may result either in dangerous underestimation of HHV-6 disease or in the institution of unnecessary antiviral therapy. Late bone marrow aplasia and late severe infections after allo-HCT without other obvious causes may be HHV-6 related., (© 2010 John Wiley & Sons A/S.)

The role of ganciclovir as HHV-6 prophylaxis in unrelated HSCT setting remains controversial. We performed an eight-yr retrospective review of patients received unrelated HSCT from January 2000 to September 2008. From January 2002, ganciclovir prophylaxis 5 mg/kg twice daily for seven days for all unrelated HSCT before transplant was adopted. The prevalence of HHV-6 encephalitis was studied before and after the change in policy. Fifty-four unrelated HSCT were performed from January 2000 to September 2008. Four cases (7.4%) of HHV-6 encephalitis were diagnosed. All of them were due to variant B infection. Two cases out of 16 cases (12.5%) were diagnosed before adoption of the policy; two cases out of 38 cases (5.3%) were diagnosed afterward. All of them were unrelated UCB transplant recipients. They were all seropositive to HHV-6 before transplant. Two cases complicated with significant residual neurological deficit and refractory seizure. The other two cases died of other transplant-related mortalities. We conclude that HHV-6 encephalitis is still a rare complication of unrelated HSCT and may be more common in unrelated UCB transplant. Routine use of ganciclovir as HHV-6 prophylaxis in all unrelated HSCT recipients may not be justified but may have a role in unrelated UCB transplant., (Copyright (c) 2009 John Wiley & Sons A/S.)

Background: Drug-Induced Hypersensitivity Syndrome (DIHS) is a severe and rare systemic reaction triggered by a drug (usually an antiepileptic drug). We present a case of DISH and we review studies on the clinical features and treatment of DIHS, and on its pathogenesis in which two elements (Herpesvirus infection and the drug) interact with the immune system to trigger such a syndrome that can lead to death in about 20% of cases., Case Presentation: We report the case of a 26-year old woman with fever, systemic maculopapular rash, lymphadenopathy, hepatitis and eosinophilic leukocytosis. She had been treated with antibiotics that gave no benefit. She was taking escitalopram and lamotrigine for a bipolar disease 30 days before fever onset. Because the patient's general condition deteriorated, betamethasone and acyclovir were started. This treatment resulted in a mild improvement of symptoms. Steroids were rapidly tapered and this was followed with a relapse of fever and a worsening of laboratory parameters. Human herpesvirus 6 (HHV-6) DNA was positive as shown by PCR. Drug-Induced Hypersensitivity Syndrome (DIHS) was diagnosed. Symptoms regressed on prednisone (at a dose of 50 mg/die) that was tapered very slowly. The patient recovered completely., Conclusions: The search for rare causes of fever led to complete resolution of a very difficult case. As DIHS is a rare disease the most relevant issue is to suspect and include it in differential diagnosis of fevers of unknown origin. Once diagnosed, the therapy is easy (steroidal administration) and often successful. However our case strongly confirms that attention should be paid on the steroidal tapering that should be very slow to avoid a relapse.

A denaturing high-performance liquid chromatography (dHPLC) assay was developed to detect antiviral drug-resistance mutations of human herpesvirus 6 (HHV-6). Recombinant baculoviruses were created that contained wild-type and mutant forms of the HHV-6 U69 gene, which determines sensitivity to the antiviral drug ganciclovir (GCV). The mutations causing GCV resistance in HHV-6 U69 were single-base mutations adapted from known GCV-resistant DNA sequences of HCMV, and their ability to confer GCV resistance on recombinant baculoviruses was confirmed. Six characterized mutant sequences, including one reported previously that encodes a GCV-sensitive kinase-activity mutant, were used. DNA was extracted, and the levels of homoduplex and heteroduplex DNA in the PCR products from mixed wild-type and mutant viral DNAs were determined using dHPLC. The optimized assay could distinguish the different mutants, and could detect mutants representing only 10% of the DNAs. The new assay with dHPLC readout permitted the rapid (4 h), objective, and reproducible detection of HHV-6 drug-resistance mutations.

Human herpesvirus 6 has rarely been identified as a cause of encephalitis in immunocompetent adults. We describe a patient who had severe encephalomyelitis, hypoglycorrhachia, and human herpesvirus 6 identified in his cerebrospinal fluid and serum and who recovered after treatment with foscarnet and ganciclovir. Human herpesvirus 6 should be considered in immunocompetent patients with encephalitis.

A 51-year-old woman with myelodysplastic syndrome developed HHV-6 encephalitis on day 34 after unrelated bone marrow transplantation. Although prompt treatment with foscarnet stabilized encephalitis and there were no serious neurological sequelae, the patient developed both hyponatremia and natriuresis 11 days after intravenous administration of foscarnet. Subsequent investigation demonstrated hyponatremia due to salt-wasting nephropathy induced by foscarnet. Discontinuation of foscarnet and fluid replacement therapy with adequate sodium chloride (NaCl) resulted in a gradual resolution of hyponatremia and natriuresis. Currently, 8 months after these clinical events, the patient is under outpatient treatment for persistent nephropathy that requires small amounts of oral NaCl supplement, but she is otherwise in good clinical condition.

Like other herpesviruses, human herpesvirus 6 (HHV-6) can reactivate in immunocompromised patients. A case is described of an HIV-1-infected patient who developed bilateral retrobulbar optic neuritis associated with HHV-6 infection. A 59-year-old woman, infected with HIV for 18 years, interrupted antiretroviral treatment because of therapeutic failure and severe metabolic complications. She presented subsequently with blurred vision and ophthalmological examination showed visual loss due to optic neuritis. Her CD4+ count was 285 cells/mm(3) and her plasma HIV-1 RNA level was 5.5 log(10) copies (cp)/ml. Magnetic resonance imaging of the brain was normal. HHV-6 loads were 3.2 log cp/ml in cerebrospinal fluid (CSF) and 6.3 log cp/10(6) peripheral blood mononuclear cells. Combined intravenous treatment was started with foscarnet and ganciclovir then changed to cidofovir and long-term valganciclovir. Her ocular condition improved gradually despite little decrease of the HHV-6 load in the CSF. Salvage antiretroviral treatment was then administered, with marked immunological and virological responses, contributing to further progressive ocular improvement. HHV-6-related optic neuritis has not been described previously in HIV-infected patients. Anti-HHV-6 treatment improved the patient's vision, but immune restoration seems to remain essential for long-term recovery.

We report a stem cell transplant recipient who developed human herpesvirus 6 encephalitis. Human herpesvirus 6 load indicated massive intrathecal viral replication. Administration of cidofovir followed by foscarnet was associated with total clearance of human herpesvirus 6 infection. Cidofovir and foscarnet combination therapy may be beneficial for reducing mortality of (neutropenic) stem cell transplant recipients with human herpesvirus 6 encephalitis.

The beta-herpesvirus human herpesvirus-6 (HHV-6) is becoming increasingly recognized as an important pathogen in immunocompromised patients, particularly in post bone marrow transplant (BMT). Reactivation of latent HHV-6 resulting in encephalitis has been reported in BMT and stem cell transplant (SCT) patients. The development of HHV-6 encephalitis can be a fatal complication, the frequency of which is increasing likely due to improved diagnosis with quantitative polymerase chain reaction (PCR) of cerebrospinal fluid. There are currently no antiviral compounds approved for HHV-6, nor have any controlled clinical trials been conducted. The frequency and severity of HHV-6 encephalitis in both immunocompetent and immunocompromised patients necessitates studies on the usefulness of currently available anti-viral compounds. The authors compared the antiviral efficacy of four drugs currently used for cytomegalovirus (CMV) infection, a beta-herpesvirus sharing homology with HHV-6. In HHV-6A- and HHV-6B-infected T cells, acyclovir, ganciclovir, foscarnet, and cidofovir exhibited antiviral activity consistent with that published in other studies. In HHV-6-infected human astrocytes (U251), however, only foscarnet and cidofovir exhibited antiviral activity and this effect was restricted to infection with HHV-6 variant A. In pathological brain sections from patients with neurological disorders such as multiple sclerosis and epilepsy, HHV-6 has been localized to glial cells. Determination of antiviral activity in human glial fibrillary acidic protein (GFAP)-positive astrocytes of currently used antiviral compounds is essential for potential treatment of HHV-6 and neurological disorders. Our data highlight the necessity for further study of antiviral compound in HHV-6-infected glial cells as well as the development of more selective compounds for HHV-6.

Human herpesvirus 6 (HHV-6) is a member of the Roseolovirus genus of the b-herpesvirus subfamily of human herpesviruses. HHV-6 infects virtually all children during the early years of life and, like other herpesviruses, establishes latency after primary infection. In immunocompromised hosts, especially transplant recipients, HHV-6 is able to reactivate and cause disease. There are two subtypes of HHV-6: type A and type B. The two subtypes share certain biological properties and a high level of sequence homology, but differ dramatically in their epidemiology. We have learned much about the epidemiology and clinical impact of HHV-6 in the decades since it was first identified, but many questions still remain. This update focuses on new findings regarding the epidemiology and clinical syndromes of HHV-6, especially as they pertain to primary infection, neurological disease, and the transplant setting. In addition, diagnostics and antiviral treatment are reviewed.

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.

Fulminant hepatitis of unknown origin remain a significant cause of mortality, for which liver transplantation is often considered as the only therapeutic option. In retrospective studies, human herpesvirus 6 (HHV-6) infections have been associated with such diseases, but the diagnosis of HHV-6 infection of the liver is rarely established during the acute phase of liver failure. Using real-time polymerase chain reaction (PCR), we diagnosed two cases of severe acute liver failure (ALF) related to HHV-6 occurring in immunocompetent young adults. Both cases had a favourable outcome, one after valganciclovir therapy, one after liver transplantation associated with ganciclovir. Viral origin was evidenced in each case by the detection of high amounts of HHV-6 DNA in liver tissue by the PCR assay. The decrease of intrahepatic viral load after therapeutic intervention was also monitored by quantitative PCR and paralleled in the two cases the clinical improvement. Diagnosis of HHV-6 infection must be systematically evoked in case of unexplained ALF, since it might lead to specific therapeutic interventions, in addition of liver transplantation.

Objective: The human Herpesvirus type-6 (HHV-6) has been implicated in multiple sclerosis (MS). Valacyclovir is an antiviral agent with an excellent safety profile. A two-year placebo-controlled, double-blind study was conducted to (1) ascertain if high-dose, prolonged treatment with valacyclovir would be safe and (2) observe if valacyclovir would delay the progression of MS clinically or by magnetic resonance imaging (MRI)., Design/methods: Fifty-eight patients were stratified as to severity and randomly assigned to receive valacyclovir (3000 mg/day) or placebo for a period of two years. Patients were followed clinically over the two-year period by means of the Expanded Disability Status Scale (EDSS), the Ambulation Index (AI) and brain MRI scans. Patients underwent routine lab studies every three months. Patients continued on the medication for two years unless they had a sustained progression or repeated exacerbations., Results: No patient discontinued the study due to side effects or toxicity. In Relative Ranking of Progression, time to first attack, attack rate, and time to withdrawal there were trends (but not statistically significant) toward drug effect over placebo in the Severe clinical category. MRI evaluation showed no significant drug effect., Conclusions: Although not statistically significant, positive trends were detected for acyclovir by clinical measures, but not by MRI.

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).

We report here a patient who suffered from PCR-confirmed human herpesvirus type 6 (HHV-6) encephalitis following reduced intensity stem cell transplantation (RIST) from her HLA-matched sibling donor. A 66-year-old woman with MDS-RA underwent RIST from her HLA-matched brother. Engraftment was favorable and grade 2 GVHD (skin and intestine) was observed with good response to 60 mg of prednisolone. On day 162, she developed fever, headache, diplopia, disorientation and abnormal neurological findings including cervical stiffness and nystagmus. An analysis of cerebrospinal fluid (CSF) revealed 80 cells/microl, a glucose level of 50 mg/dl and a protein level of 97 mg/dl on day 162. Although computed tomography (CT) of the brain and electroencephalography (EEG) were nonspecific, HHV-6 was detected in the CSF using polymerase chain reaction (PCR) techniques and the patient was diagnosed as having encephalitis due to local reactivation of HHV-6. Administration of ganciclovir (GCV) and acyclovir (ACV) were started from day 162. Treatment with antiviral agents was effective, with total resolution of her symptoms and the DNA of this virus disappeared from the CSF after 23 days of treatment. This case shows that HHV-6 infection has to be considered in patients with neurological symptoms following stem cell transplantation, and suggests the necessity of PCR for HHV-6 virus from the CSF.

We report a case of human herpesvirus 6 (HHV-6) encephalomyelitis in an immunocompetent patient, which was confirmed by viral amplification from cerebrospinal fluid. Cidofovir was used, followed by ganciclovir, because of an adverse effect to probenecid. The patient recovered. HHV-6 should be recognized as one of the causes of encephalomyelitis.

Viral infections are potentially associated with the etiology and pathogenesis of multiple sclerosis (MS). It has been speculated that the treatment efficacy of interferon beta (IFN beta) in MS may relate to its anti-viral properties. The study was undertaken to evaluate the in vivo anti-viral effects of IFN beta-1a in patients with MS. Human herpesvirus-6 (HHV-6) was studied as an example for being a latent neurotropic virus. IFN beta used at concentrations of approximately 0.5 microg/ml was shown to significantly reduce in vitro HHV-6 replication in a susceptible T-cell line. Sera derived from 23 MS patients treated with IFN beta-1a were examined for serum cell-free DNA of HHV-6 as an indicator for viral replication and the reactivity of IgM antibodies to a recombinant HHV-6 virion protein containing a known immunoreactive region. The results were compared with those of control sera obtained from untreated MS (n=29) and healthy individuals (n=21). The findings indicated that IFN beta treatment significantly reduced HHV-6 replication as evident by decreased cell-free DNA in treated MS specimens. The results correlated with decreased IgM reactivity to the HHV-6 antigen in treated MS patients compared to untreated controls, suggesting reduced exposure to HHV-6. The findings were confirmed in paired sera obtained from seven MS patients before and after the treatment The study provides new evidence indicating that IFN beta has potent in vivo anti-viral effects that may contribute to the treatment efficacy in MS.

Human herpesvirus 6 (HHV-6) infection and disease are serious complications of allogeneic hematopoietic stem cell transplantation (allo-SCT). Ganciclovir (GCV) is effective against HHV-6 in vitro but the antiviral susceptibility of HHV-6 has not been well characterized in vivo. We retrospectively compared the HHV-6 reactivation rate in pediatric allo-SCT recipients with and without GCV prophylaxis. The HHV-6 reactivation rate at 3 weeks after allo-SCT in patients without prophylactic GCV administration was significantly higher than that in those receiving prophylactic GCV (11/28 vs 0/13, P < 0.01). Five of 36 patients without prophylactic GCV showed clinical manifestations including skin rash, interstitial pneumonitis, persistent thrombocytopenia, enterocolitis and thrombotic microangiopathy, respectively. HHV-6-associated symptoms were observed in one of the 13 patients receiving prophylactic GCV. This patient showed fever, diarrhea and graft rejection concomitantly with a sudden increase of HHV-6 DNA copy number. Patients who received GCV for treatment of HHV-6 infection showed an improvement in symptoms and/or decrease of HHV-6 copy number. Thus, GCV is effective for treating HHV-6 disease after allo-SCT in vivo.