Coinfection of human herpesviruses 6A (HHV-6A) and HHV-6B as demonstrated by novel digital droplet PCR assay

Development and validation of a novel multiplex digital PCR assay for identification of pathogens in cerebrospinal fluid of children with bacterial meningitis

BACKGROUND AND AIMS

Identifying the pathogens of bacterial meningitis (BM) is crucial for its diagnosis and treatment. The aim of this study is to develop and validate a novel method for detecting pathogens in cerebrospinal fluid (CSF) of children with BM using a digital polymerase chain reaction (dPCR) assay.

MATERIALS AND METHODS

A novel multiplex dPCR assay method has been developed and validated. The diagnostic performance of the dPCR assay was compared with that of synchronous CSF culture, and the factors affecting its performance were analyzed.

RESULTS

A total of 69 children with BM were enrolled prospectively. The sensitivity of the dPCR assay was 94.44 %, specificity was 100 %, coincidence rate was 98.55 %, Kappa value was 0.959, and net reclassification improvement was 61.11 %. Compared with the CSF culture assay, the dPCR assay had higher sensitivity in different bacterial groups. Multiple factors affected its performance, including previous use of antibiotics, sampling time, BM complications, and levels of inflammatory biomarkers in CSF and blood (all P < 0.05). Patients who required intensive care and died had a higher bacterial DNA loads identified by dPCR assay (both P < 0.05).

CONCLUSION

This novel assay has better pathogen detection ability than CSF culture. Its performance was influenced by sampling time, previous use of antibiotics, and disease severity.

Detecting plasma hsa_circ_0061276 in patients with gastric cancer by reverse transcription-digital polymerase chain reaction

Background

The role of circular RNAs (circRNAs) in the occurrence of gastric cancer is still unclear. Therefore, the diagnostic value and mechanisms underlying hsa_circ_0061276 in the occurrence of gastric cancer were explored.

Methods

Reverse transcription-droplet digital polymerase chain reaction was used to detect the copy number of hsa_circ_0061276 in plasma from healthy individuals, as well as from patients with gastric precancerous lesions or early-stage or advanced gastric cancer. Plasmids overexpressing or knocking down hsa_circ_0061276 expression were transfected into gastric cancer cells. The effects on the growth, migration, and cell cycle distribution of gastric cancer cells were then analyzed. Finally, miRanda and RNAhybrid were used to explore the binding sites between hsa_circ_0061276 and microRNAs (miRNAs). A double luciferase reporter gene assay was used to confirm the miRNA sponge effect.

Results

The results show that plasma hsa_circ_0061276 copy number showed a trend of a gradual decrease when comparing healthy controls to the early cancer group and advanced gastric cancer group. Overexpression of hsa_circ_0061276 inhibited the growth and migration of gastric cancer cells. Through bioinformatic analyses combined with cellular experiments, it was found that hsa_circ_0061276 inhibited the growth of gastric cancer by binding to hsa-miR-7705.

Conclusion

Hsa_circ_0061276 may be a new biomarker for gastric cancer. The tumor suppressor role of hsa_circ_0061276 on gastric cancer likely occurs through a sponge effect on miRNAs such as hsa-miR-7705.

Viral Coinfections

In nature, viral coinfection is as widespread as viral infection alone. Viral coinfections often cause altered viral pathogenicity, disrupted host defense, and mixed-up clinical symptoms, all of which result in more difficult diagnosis and treatment of a disease. There are three major virus-virus interactions in coinfection cases: viral interference, viral synergy, and viral noninterference. We analyzed virus-virus interactions in both aspects of viruses and hosts and elucidated their possible mechanisms. Finally, we summarized the protocol of viral coinfection studies and key points in the process of virus separation and purification.

Family Herpesviridae and neuroinfections: current status and research in progress

This article addresses the relationship between human herpesviruses (HHVs) and neuroinfections. Alphaherpesviruses, betaherpesviruses and gammaherpesviruses are neurotropic viruses that establish latency and exhibit reactivation capacity. Encephalitis and meningitis are common in cases of HHV. The condition promoted by HHV infection is a purported trigger for certain neurodegenerative diseases. Ongoing studies have identified an association between HSV-1 and the occurrence of Alzheimer's disease, multiple sclerosis and infections by HHV-6 and Epstein-Barr virus. In this review, we highlight the importance of research investigating the role of herpesviruses in the pathogenesis of diseases that affect the nervous system and describe other studies in progress.

Comparison of qPCR with ddPCR for the Quantification of JC Polyomavirus in CSF from Patients with Progressive Multifocal Leukoencephalopathy

Background: Lytic infection of oligodendrocytes by the human JC polyomavirus (JCPyV) results in the demyelinating disease called progressive multifocal leukoencephalopathy (PML). The detection of viral DNA in the cerebrospinal fluid (CSF) by PCR is an important diagnostic tool and, in conjunction with defined radiological and clinical features, can provide diagnosis of definite PML, avoiding the need for brain biopsy. The main aim of this study is to compare the droplet digital PCR (ddPCR) assay with the gold standard quantitative PCR (qPCR) for the quantification of JC viral loads in clinical samples. Methods: A total of 62 CSF samples from 31 patients with PML were analyzed to compare the qPCR gold standard technique with ddPCR to detect conserved viral DNA sequences in the JCPyV genome. As part of the validation process, ddPCR results were compared to qPCR data obtained in 42 different laboratories around the world. In addition, the characterization of a novel triplex ddPCR to detect viral DNA sequence from both prototype and archetype variants and a cellular housekeeping reference gene is described. Triplex ddPCR was used to analyze the serum from six PML patients and from three additional cohorts, including 20 healthy controls (HC), 20 patients with multiple sclerosis (MS) who had never been treated with natalizumab (no-NTZ-treated), and 14 patients with MS who were being treated with natalizumab (NTZ-treated); three from this last group seroconverted during the course of treatment with natalizumab. Results: JCPyV DNA was detected only by ddPCR for 5 of the 62 CSF samples (8%), while remaining undetected by qPCR. For nine CSF samples (15%), JCPyV DNA was at the lower limit of quantification for qPCR, set at <250 copies/mL, and therefore no relative quantitation could be determined. By contrast, exact copies of JCPyV for each of these samples were quantified by ddPCR. No differences were observed between qPCR and ddPCR when five standardized plasma samples were analyzed for JCPyV in 42 laboratories in the United States and Europe. JCPyV-DNA was undetected in all the sera from HC and MS cohorts tested by triplex ddPCR, while serum samples from six patients with PML tested positive for JCPyV. Conclusion: This study shows strong correlation between ddPCR and qPCR with increased sensitivity of the ddPCR assay. Further work will be needed to determine whether multiplex ddPCR can be useful to determine PML risk in natalizumab-treated MS patients.

Human Herpesvirus 6A Is a Risk Factor for Multiple Sclerosis

The role for human herpesvirus (HHV)-6A or HHV-6B in multiple sclerosis (MS) pathogenesis has been controversial. Possibly because the damage of the virus infection may occur before onset of clinical symptoms and because it has been difficult to detect active infection and separate serological responses to HHV-6A or 6B. Recent studies report that in MS patients the serological response against HHV-6A is increased whereas it is decreased against HHV-6B. This effect seems to be even more pronounced in MS patients prior to diagnosis and supports previous studies postulating a predomination for HHV-6A in MS disease and suggests that the infection is important at early stages of the disease. Furthermore, HHV-6A infection interacts with other factors suspected of modulating MS susceptibility and progression such as infection with Epstein-Barr virus (EBV) and Cytomegalovirus (CMV), tobacco smoking, HLA alleles, UV irradiation and vitamin D levels. The multifactorial nature of MS and pathophysiological role for HHV-6A in inflammation and autoimmunity are discussed.

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.

Investigation of Inherited Chromosomally Integrated Human Herpesvirus-6A+ and -6B+ in a Patient with Ulipristal Acetate-Induced Fulminant Hepatic Failure

Inherited chromosomally integrated (ici) human herpes virus 6 (HHV-6) is estimated to occur in 0.6–2.7% of people worldwide. HHV-6 comprises two distinct species: HHV-6A and HHV-6B. Both HHV-6A and HHV-6B integration have been reported. Several drugs are capable of activating iciHHV-6 in tissues, the consequences of which are poorly understood. We report herein a case of a woman with iciHHV-6A+ and iciHHV-6B+, who developed ulipristal acetate (a selective progesterone receptor modulator)-induced fulminant hepatic failure that required liver transplantation. We confirmed the presence of ~one copy per cell of both HHV-6A and HHV-6B DNA in her hair follicles using multiplex HHV-6A/B real-time PCR and demonstrated the Mendelian inheritance of both iciHHV-6A and iciHHV-6B in her family members over three generations. Because of the rarity of this presentation, we discuss herein the possible links between reactivated HHV-6 from iciHHV-6A and/or iciHHV-6B and adverse drug reactions, suggesting that iciHHV-6 could be screened before the introduction of any hepatotoxic drugs to exclude HHV-6 active disease or combined idiosyncratic drug-induced liver injury in these patients.

Droplet digital PCR of viral ‎DNA/RNA, current progress, challenges, and future perspectives

High-throughput droplet-based digital PCR (ddPCR) is a refinement of the conventional polymerase chain reaction (PCR)‎ methods. In ddPCR, DNA/RNA is encapsulated stochastically inside the microdroplets as reaction chambers. A small percentage of the reaction chamber contains one or fewer copies of the DNA or RNA. After PCR amplification, concentrations are determined based on the proportion of nonfluorescent partitions through the Poisson distribution. Some of the main features of ddPCR include high sensitivity and specificity, absolute quantification without a standard curve, high reproducibility, good tolerance to PCR inhibitor, and high efficacy compared to conventional molecular methods. These advantages make ddPCR a valuable addition to the virologist's toolbox. The following review outlines the recent technological advances in ddPCR methods and their applications in viral identification.

Digital PCR for accurate quantification of pathogens: Principles, applications, challenges and future prospects

Pathogens pose a severe threat to food safety and human health. The traditional methods for pathogen detection can't meet the growing diagnosis and control need. Digital PCR (dPCR) attracts a considerable attention for its ability to absolutely quantify pathogens with features of high selectivity, simplicity, accuracy and rapidity. The dPCR technique that achieves absolute quantification based on end-point measurement without standard curve offers a guideline for further genetic analysis and molecular diagnosis. It could contribute to the quantification of low level of nucleic acid, early detection and timely prevention of pathogenic diseases. In this review, 1442 publications about dPCR were selected and the detections of various pathogens by dPCR were reviewed comprehensively, including viruses, bacteria, parasites and fungi. A number of examples are cited to illustrate that dPCR is a new powerful tool with desired accuracy, sensitivity, and reproducibility for quantification of different types of pathogens. Moreover, the benefits, challenges and future prospects of the dPCR were also highlighted in this review.

Evolutionary History of Endogenous Human Herpesvirus 6 Reflects Human Migration out of Africa

Human herpesvirus 6A and 6B (HHV-6) can integrate into the germline, and as a result, ∼70 million people harbor the genome of one of these viruses in every cell of their body. Until now, it has been largely unknown if 1) these integrations are ancient, 2) if they still occur, and 3) whether circulating virus strains differ from integrated ones. Here, we used next-generation sequencing and mining of public human genome data sets to generate the largest and most diverse collection of circulating and integrated HHV-6 genomes studied to date. In genomes of geographically dispersed, only distantly related people, we identified clades of integrated viruses that originated from a single ancestral event, confirming this with fluorescent in situ hybridization to directly observe the integration locus. In contrast to HHV-6B, circulating and integrated HHV-6A sequences form distinct clades, arguing against ongoing integration of circulating HHV-6A or “reactivation” of integrated HHV-6A. Taken together, our study provides the first comprehensive picture of the evolution of HHV-6, and reveals that integration of heritable HHV-6 has occurred since the time of, if not before, human migrations out of Africa.

Differential activation of neuroinflammatory pathways in children with seizures: A cross-sectional study

PURPOSE

Inflammation plays a crucial role in epileptogenesis. We analyzed inflammatory cytokines in plasma and saliva from children with seizures and healthy controls and measured their associations with HHV6 and EBV infection.

METHODS

We analyzed plasma from 36 children within 24 h of seizures (cases) and 43 healthy controls and saliva from 44 cases and 44 controls with a multiplex immunoassay. Saliva from all controls and 65 cases and blood from 26 controls and 35 cases were also analyzed by PCR for viral DNA. Primary outcome was cytokine levels in cases vs. controls. Secondary outcomes included detection of HHV-6 and EBV viral DNA in cases vs. controls and viral loads in cases vs. controls. Statistical analysis included the Wilcoxon Rank Sum test, Fisher's exact test, ANOVA, and Spearman correlation.

RESULTS

Compared to controls, patients had higher levels of CCL11 (p = 0.0018), CCL26 (p<0.001), IL10 (p = 0.044), IL6 (p<0.001), IL8 (p = 0.018), and MIP1β (p = 0.0012). CCL11 was higher with 3 or more seizures (p = 0.01), seizures longer than 10 min (p = 0.001), and when EEG showed focal slowing (p = 0.02). In saliva, febrile seizures had higher levels of IL-1β (n = 7, p = 0.04) and new onset seizures had higher IL-6 (n = 15, p = 0.02). Plasma and saliva cytokine levels did not show a correlation. The frequency of HHV-6 and EBV detection was similar across groups and not different than controls. We found no correlation between viral load and cytokine levels.

CONCLUSIONS

We showed differential activation of neuroinflammatory pathways in plasma from different seizure etiologies compared to controls, unrelated to viral infection.

Variation in human herpesvirus 6B telomeric integration, excision, and transmission between tissues and individuals

Human herpesviruses 6A and 6B (HHV-6A/6B) are ubiquitous pathogens that persist lifelong in latent form and can cause severe conditions upon reactivation. They are spread by community-acquired infection of free virus (acqHHV6A/6B) and by germline transmission of inherited chromosomally integrated HHV-6A/6B (iciHHV-6A/6B) in telomeres. We exploited a hypervariable region of the HHV-6B genome to investigate the relationship between acquired and inherited virus and revealed predominantly maternal transmission of acqHHV-6B in families. Remarkably, we demonstrate that some copies of acqHHV-6B in saliva from healthy adults gained a telomere, indicative of integration and latency, and that the frequency of viral genome excision from telomeres in iciHHV-6B carriers is surprisingly high and varies between tissues. In addition, newly formed short telomeres generated by partial viral genome release are frequently lengthened, particularly in telomerase-expressing pluripotent cells. Consequently, iciHHV-6B carriers are mosaic for different iciHHV-6B structures, including circular extra-chromosomal forms that have the potential to reactivate. Finally, we show transmission of an HHV-6B strain from an iciHHV-6B mother to her non-iciHHV-6B son. Altogether, we demonstrate that iciHHV-6B can readily transition between telomere-integrated and free virus forms.

Viral infections and their relationship to neurological disorders

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

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

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

Development and optimization of a simian immunodeficiency virus (SIV) droplet digital PCR (ddPCR) assay

Accurate and sensitive quantification of rebound competent HIV that persists despite combination antiretroviral treatment (cART), including in latently infected cells (i.e., viral reservoir), is critical for evaluating cure strategies for decreasing or eliminating this reservoir. Simian immunodeficiency virus (SIV)-infected Rhesus macaques are an important non-human primate (NHP) system for studying potential cure strategies as they model many key aspects of human HIV-infection including the persistence of a latent viral reservoir in resting memory CD4+ T cells in animals receiving prolonged cART. In this report, we describe the design and testing of a sensitive SIV droplet digital PCR (ddPCR) assay through exploring the combination and optimization of different probe systems (including single, double quencher probes and minor groove binder (MGB) probes) and reaction conditions to eliminate background signal(s), ensure distinct target signal cluster separation from non-target signals, and enable detection and quantification of low level authentic target signals. Similar reaction conditions and assay validation procedures can be explored for potential development of additional assays for other applications that require sensitive detection of low-level targets in a large background of nucleic acid input derived from cell or tissue sources.

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

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

HERQ-9 Is a New Multiplex PCR for Differentiation and Quantification of All Nine Human Herpesviruses

By adulthood, almost all humans become infected by at least one herpesvirus (HHV). The maladies inflicted by these microbes extend beyond the initial infection, as they remain inside our cells for life and can reactivate, causing severe diseases. The diagnosis of active infection by these ubiquitous pathogens includes the detection of DNA with sensitive and specific assays. We developed the first quantitative PCR assay (HERQ-9) designed to identify and quantify each of the nine human herpesviruses. The simultaneous detection of HHVs in the same sample is important since they may act together to induce life-threatening conditions. Moreover, the high sensitivity of our method is of extreme value for assessment of the effects of these viruses persisting in our body and their long-term consequences on our health.

Infections with the nine human herpesviruses (HHVs) are globally prevalent and characterized by lifelong persistence. Reactivations can potentially manifest as life-threatening conditions for which the demonstration of viral DNA is essential. In the present study, we developed HERQ-9, a pan-HHV quantitative PCR designed in triplex reactions to differentiate and quantify each of the HHV-DNAs: (i) herpes simplex viruses 1 and 2 and varicella-zoster virus; (ii) Epstein-Barr virus, human cytomegalovirus, and Kaposi’s sarcoma-associated herpesvirus; and (iii) HHV-6A, -6B, and -7. The method was validated with prequantified reference standards as well as with mucocutaneous swabs and cerebrospinal fluid, plasma, and tonsillar tissue samples. Our findings highlight the value of multiplexing in the diagnosis of many unsuspected, yet clinically relevant, herpesviruses. In addition, we report here frequent HHV-DNA co-occurrences in clinical samples, including some previously unknown. HERQ-9 exhibited high specificity and sensitivity (LOD₉₅s of ∼10 to ∼17 copies/reaction), with a dynamic range of 10¹ to 10⁶ copies/μl. Moreover, it performed accurately in the coamplification of both high- and low-abundance targets in the same reaction. In conclusion, we demonstrated that HERQ-9 is suitable for the diagnosis of a plethora of herpesvirus-related diseases. Besides its significance to clinical management, the method is valuable for the assessment of hitherto-unexplored synergistic effects of herpesvirus coinfections. Furthermore, its high sensitivity enables studies on the human virome, often dealing with minute quantities of persisting HHVs.

IMPORTANCE By adulthood, almost all humans become infected by at least one herpesvirus (HHV). The maladies inflicted by these microbes extend beyond the initial infection, as they remain inside our cells for life and can reactivate, causing severe diseases. The diagnosis of active infection by these ubiquitous pathogens includes the detection of DNA with sensitive and specific assays. We developed the first quantitative PCR assay (HERQ-9) designed to identify and quantify each of the nine human herpesviruses. The simultaneous detection of HHVs in the same sample is important since they may act together to induce life-threatening conditions. Moreover, the high sensitivity of our method is of extreme value for assessment of the effects of these viruses persisting in our body and their long-term consequences on our health.

Human Herpesvirus 6 Detection in Alzheimer's Disease Cases and Controls across Multiple Cohorts

The interplay between viral infection and Alzheimer's disease (AD) has long been an area of interest, but proving causality has been elusive. Several recent studies have renewed the debate concerning the role of herpesviruses, and human herpesvirus 6 (HHV-6) in particular, in AD. We screened for HHV-6 detection across three independent AD brain repositories using (1) RNA sequencing (RNA-seq) datasets and (2) DNA samples extracted from AD and non-AD control brains. The RNA-seq data were screened for pathogens against taxon references from over 25,000 microbes, including 118 human viruses, whereas DNA samples were probed for PCR reactivity to HHV-6A and HHV-6B. HHV-6 demonstrated little specificity to AD brains over controls by either method, whereas other viruses, such as Epstein-Barr virus (EBV) and cytomegalovirus (CMV), were detected at comparable levels. These direct methods of viral detection do not suggest an association between HHV-6 and AD.

Entering the Pantheon of 21st Century Molecular Biology Tools: A Perspective on Digital PCR

After several decades of relatively modest use, in the last several years digital PCR (dPCR) has grown to become the new gold standard for nucleic acid quantification. This coincides with the commercial availability of scalable, affordable, and reproducible droplet-based dPCR platforms in the past five years and has led to its rapid dissemination into diverse research fields and testing applications. Among these, it has been adopted most vigorously into clinical oncology where it is beginning to be used for plasma genotyping in cancer patients undergoing treatment. Additionally, innovation across the scientific community has extended the benefits of reaction partitioning beyond DNA and RNA quantification alone, and demonstrated its usefulness in evaluating DNA size and integrity, the physical linkage of colocalized markers, levels of enzyme activity and specific cation concentrations in a sample, and more. As dPCR technology gains in popularity and breadth, its power and simplicity can often be taken for granted; thus, the reader is reminded that due diligence must be exercised in order to make claims not only of precision but also of accuracy in their measurements.

Herpesvirus trigger accelerates neuroinflammation in a nonhuman primate model of multiple sclerosis

Pathogens, particularly human herpesviruses (HHVs), are implicated as triggers of disease onset/progression in multiple sclerosis (MS) and other neuroinflammatory disorders. However, the time between viral acquisition in childhood and disease onset in adulthood complicates the study of this association. Using nonhuman primates, we demonstrate that intranasal inoculations with HHV-6A and HHV-6B accelerate an MS-like neuroinflammatory disease, experimental autoimmune encephalomyelitis (EAE). Although animals inoculated intranasally with HHV-6 (virus/EAE marmosets) were asymptomatic, they exhibited significantly accelerated clinical EAE compared with control animals. Expansion of a proinflammatory CD8 subset correlated with post-EAE survival in virus/EAE marmosets, suggesting that a peripheral (viral?) antigen-driven expansion may have occurred post-EAE induction. HHV-6 viral antigen in virus/EAE marmosets was markedly elevated and concentrated in brain lesions, similar to previously reported localizations of HHV-6 in MS brain lesions. Collectively, we demonstrate that asymptomatic intranasal viral acquisition accelerates subsequent neuroinflammation in a nonhuman primate model of MS.

Prevalence of salivary human herpesviruses in pediatric multiple sclerosis cases and controls

BACKGROUND

Multiple sclerosis (MS) is a multifactorial disease of unknown origin. The current paradigm is that disease develops in genetically susceptible individuals, influenced by environmental factors. Epstein-Barr virus (EBV) and human herpesvirus 6 (HHV-6) have particularly strong associations with the disease. Both viruses are typically acquired during childhood, decades before MS presents. However, in patients with pediatric MS, the temporal window between viral acquisition and disease onset is shortened, which may provide insights into the association of herpesviruses with MS.

OBJECTIVE

To compare the frequency of EBV and HHV-6 in the saliva of a cohort of pediatric MS patients and age-matched controls.

METHODS

The study enrolled 32 pediatric MS patients and 42 controls and evaluated saliva for HHV-6 u57 and EBV lmp-1 amplification by droplet digital polymerase chain reaction (ddPCR).

RESULTS

Pediatric MS patients did not differ from controls in the frequency or magnitude of salivary viral shedding. During the assessment of EBV positivity, distinct profiles emerged that correlated with target amplicon mutations.

CONCLUSIONS

None of these mutations were evident in EBV-positive samples from pediatric MS patients, whereas they were present in pediatric controls, in addition to MS and control adults, suggesting differential host-immune control of EBV in this pediatric MS cohort.

Using Droplet Digital PCR to Detect Coinfection of Human Herpesviruses 6A and 6B (HHV-6A and HHV-6B) in Clinical Samples

Droplet digital™ polymerase chain reaction (ddPCR™) is a unique digital PCR technique that allows for absolute quantification of nucleic acid samples. This technique operates on the basis of amplification within water-oil emulsion droplets and can detect very small quantities of target molecules, yielding extremely precise data. Here, we describe in detail a ddPCR procedure for multiplexed detection of two clinically relevant herpesviruses, HHV-6A and HHV-6B.

CD8+ T Cells Prevent Lethality from Neonatal Murine Roseolovirus Infection

A recently described mouse homolog of the human roseoloviruses, murine roseolovirus (MRV), causes loss of peripheral and thymic CD4+ cells during neonatal infection of BALB/c mice. Despite significant disruptions to the normal adaptive immune response, infected BALB/c mice reproducibly recover from infection, consistent with prior studies on a related virus, mouse thymic virus. In this article, we show that, in contrast to published studies on mouse thymic virus, MRV appears to robustly infect neonatal C57BL/6 (B6) mice, causing severe depletion of thymocytes and peripheral T cells. Moreover, B6 mice recovered from infection. We investigated the mechanism of thymocyte and T cell loss, determining that the major thymocyte subsets were infected with MRV; however, CD4+ and CD4+CD8- T cells showed increased apoptosis during infection. We found that CD8+ T cells populated MRV-infected thymi. These CD8+ T cells expressed markers of activation, had restricted TCR repertoire, and accumulated intracellular effector proteins, consistent with a cytotoxic lymphocyte phenotype and suggesting their involvement in viral clearance. Indeed, absence of CD8+ T cells prevented recovery from MRV infection and led to lethality in infected animals, whereas B cell-deficient mice showed CD4+ T cell loss but recovered from infection without lethality. Thus, these results demonstrate that CD8+ T cells are required for protective immunity against a naturally occurring murine pathogen that infects the thymus and establish a novel infection model for MRV in B6 mice, providing the foundation for detailed future studies on MRV with the availability of innumerable mutant mice on the B6 background.

A comparative study of digital PCR and real-time qPCR for the detection and quantification of HPV mRNA in sentinel lymph nodes of cervical cancer patients

Background

Qualitative analyses showed that the presence of HPV mRNA in sentinel lymph nodes of cervical cancer patients with pN0 status is associated with significantly decreased recurrence free survival. To further address the clinical potential of the strategy and to define prognostic threshold levels it is necessary to use a quantitative assay. Here, we compare two methods of quantification: digital PCR and standard quantitative PCR.

Methods

Serial dilutions of 5 ng–5 pg RNA (≙ 500–0.5 cells) of the cervical cancer cell line SiHa were prepared in 5 µg RNA of the HPV-negative human keratinocyte cell line HaCaT. Clinical samples consisted of 10 sentinel lymph nodes with varying HPV transcript levels. Reverse transcription of total RNA (5 µg RNA each) was performed in 100 µl and cDNA aliquots were analyzed by qPCR and dPCR. Digital PCR was run in the RainDrop^® Digital PCR system (RainDance Technologies) using a probe-based detection of HPV E6/E7 cDNA PCR products with 11 µl template. qPCR was done using a Rotor Gene Q 5plex HRM (Qiagen) amplifying HPV E6/E7 cDNA in a SYBR Green format with 1 µl template.

Results

For the analysis of both, clinical samples and serial dilution samples, dPCR and qPCR showed comparable sensitivity. With regard to reproducibility, both methods differed considerably, especially for low template samples. Here, we found with qPCR a mean variation coefficient of 126% whereas dPCR enabled a significantly lower mean variation coefficient of 40% (p = 0.01). Generally, we saw with dPCR a substantial reduction of subsampling errors, which most likely reflects the large cDNA amounts available for analysis.

Conclusions

Compared to real-time PCR, dPCR shows higher reliability. Thus, our HPV mRNA dPCR assay holds promise for the clinical evaluation of occult tumor cells in histologically tumor-free lymph nodes in future studies.

Electronic supplementary material

The online version of this article (10.1186/s13104-017-2846-8) contains supplementary material, which is available to authorized users.

Transmission Fitness in Co-colonization and the Persistence of Bacterial Pathogens

Humans are often colonized by polymorphic bacteria such as Streptococcus pneumoniae, Bordetella pertussis, Staphylococcus Aureus, and Haemophilus influenzae. Two co-colonizing pathogen clones may interact with each other upon host entry and during within-host dynamics, ranging from competition to facilitation. Here we examine the significance of these exploitation strategies for bacterial spread and persistence in host populations. We model SIS epidemiological dynamics to capture the global behavior of such multi-strain systems, focusing on different parameters of single and dual colonization. We analyze the impact of heterogeneity in clearance and transmission rates of single and dual colonization and find the criteria under which these asymmetries enhance endemic persistence. We obtain a backward bifurcation near [Formula: see text] if the reproductive value of the parasite in dually infected hosts is sufficiently higher than that in singly infected ones. In such cases, the parasite is able to persist even in sub-threshold conditions, and reducing the basic reproduction number below 1 would be insufficient for elimination. The fitness superiority in co-colonized hosts can be attained by lowering net parasite clearance rate ([Formula: see text]), by increasing transmission rate ([Formula: see text]), or both, and coupling between these traits critically constrains opportunities of pathogen survival in the [Formula: see text] regime. Finally, using an adaptive dynamics approach, we verify that despite their importance for sub-threshold endemicity, traits expressed exclusively in coinfection should generally evolve independently of single infection traits. In particular, for [Formula: see text] a saturating parabolic or hyperbolic function of [Formula: see text], co-colonization traits evolve to an intermediate optimum (evolutionarily stable strategy, ESS), determined only by host lifespan and the trade-off parameters linking [Formula: see text] and [Formula: see text]. Our study invites more empirical attention to the dynamics and evolution of parasite life-history traits expressed exclusively in coinfection.

Chromosomally Integrated Human Herpesvirus 6: Models of Viral Genome Release from the Telomere and Impacts on Human Health

Human herpesvirus 6A and 6B, alongside some other herpesviruses, have the striking capacity to integrate into telomeres, the terminal repeated regions of chromosomes. The chromosomally integrated forms, ciHHV-6A and ciHHV-6B, are proposed to be a state of latency and it has been shown that they can both be inherited if integration occurs in the germ line. The first step in full viral reactivation must be the release of the integrated viral genome from the telomere and here we propose various models of this release involving transcription of the viral genome, replication fork collapse, and t-circle mediated release. In this review, we also discuss the relationship between ciHHV-6 and the telomere carrying the insertion, particularly how the presence and subsequent partial or complete release of the ciHHV-6 genome may affect telomere dynamics and the risk of disease.

Human Herpesviruses 6A, 6B, and 7

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.

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.

Development of neurologic diseases in a patient with primate T lymphotropic virus type 1 (PTLV-1)

Background

Virus transmission from various wild and domestic animals contributes to an increased risk of emerging infectious diseases in human populations. HTLV-1 is a human retrovirus associated with acute T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 originated from ancient zoonotic transmission from nonhuman primates, although cases of zoonotic infections continue to occur. Similar to HTLV-1, the simian counterpart, STLV-1, causes chronic infection and leukemia and lymphoma in naturally infected monkeys, and combined are called primate T-lymphotropic viruses (PTLV-1). However, other clinical syndromes typically seen in humans such as a chronic progressive myelopathy have not been observed in nonhuman primates. Little is known about the development of neurologic and inflammatory diseases in human populations infected with STLV-1-like viruses following nonhuman primate exposure.

Results

We performed detailed laboratory analyses on an HTLV-1 seropositive patient with typical HAM/TSP who was born in Liberia and now resides in the United States. Using a novel droplet digital PCR for the detection of the HTLV-1 tax gene, the proviral load in PBMC and cerebrospinal fluid cells was 12.98 and 51.68 %, respectively; however, we observed a distinct difference in fluorescence amplitude of the positive droplet population suggesting possible mutations in proviral DNA. A complete PTLV-1 proviral genome was amplified from the patient’s PBMC DNA using an overlapping PCR strategy. Phylogenetic analysis of the envelope and LTR sequences showed the virus was highly related to PTLV-1 from sooty mangabey monkeys (smm) and humans exposed via nonhuman primates in West Africa.

Conclusions

These results demonstrate the patient is infected with a simian variant of PTLV-1, suggesting for the first time that PTLV-1smm infection in humans may be associated with a chronic progressive neurologic disease.

Human herpesvirus multiplex ddPCR detection in brain tissue from low- and high-grade astrocytoma cases and controls

Background

Glioblastoma (GBM) is a fatal CNS malignancy, representing 50 % of all gliomas with approximately 12–18 months survival time after initial diagnosis. Recently, the human herpesvirus cytomegalovirus (CMV) has been suggested to have an oncogenic role, yet this association remains controversial. In addition, human herpesvirus 6 (HHV-6) and Epstein-Barr virus (EBV) have also been associated with low-grade gliomas, but few studies have examined HHV-6 and EBV in glioblastomas. Droplet digital PCR (ddPCR) is a highly precise diagnostic tool that enables the absolute quantification of target DNA. This study examines the association between multiple human herpesviruses and astrocytomas.

Methods

This study analyzed 112 brain tissue specimens, including 45 glioblastoma, 12 astrocytoma grade III, 2 astrocytoma grade II, 4 astrocytoma grade I, and 49 controls. All brain tissue samples were de-identified and pathologically confirmed. Each tissue block was sectioned for DNA extraction and CMV, EBV, HHV-6A and HHV-6B, and a cellular housekeeping gene were amplified by ddPCR.

Results

Neither CMV nor HHV-6A were detected in any of the astrocytoma samples. However, HHV-6B (p = 0.147) and EBV (p = 0.049) had a higher positivity frequency in the GBM compared to the controls.

Conclusion

The undetectable CMV DNA in the astrocytoma cohort does not support the observation of an increased prevalence of CMV DNA in GBM, as reported in other studies. EBV has a significantly higher positivity in the GBM cohort compared to the controls, while HHV-6B has a higher but not statistically significant positivity in the case cohort. Whether these viruses play an oncogenic role in GBM remains to be further investigated.

Detection of Human Herpesvirus 6B (HHV-6B) Reactivation in Hematopoietic Cell Transplant Recipients with Inherited Chromosomally Integrated HHV-6A by Droplet Digital PCR

The presence of inherited chromosomally integrated human herpesvirus 6 (ciHHV-6) in hematopoietic cell transplant (HCT) donors or recipients confounds molecular testing for HHV-6 reactivation, which occurs in 30 to 50% of transplants. Here we describe a multiplex droplet digital PCR clinical diagnostic assay that concurrently distinguishes between HHV-6 species (A or B) and identifies inherited ciHHV-6. By applying this assay to recipient post-HCT plasma and serum samples, we demonstrated reactivation of HHV-6B in 25% (4/16 recipients) of HCT recipients with donor- or recipient-derived inherited ciHHV-6A, underscoring the need for diagnostic testing for HHV-6 infection even in the presence of ciHHV-6.

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.

Standard free droplet digital polymerase chain reaction as a new tool for the quality control of high-capacity adenoviral vectors in small-scale preparations

High-capacity adenoviral vectors (HCAdVs) are promising tools for gene therapy as well as for genetic engineering. However, one limitation of the HCAdV vector system is the complex, time-consuming, and labor-intensive production process and the following quality control procedure. Since HCAdVs are deleted for all viral coding sequences, a helper virus (HV) is needed in the production process to provide the sequences for all viral proteins in trans. For the purification procedure of HCAdV, cesium chloride density gradient centrifugation is usually performed followed by buffer exchange using dialysis or comparable methods. However, performing these steps is technically difficult, potentially error-prone, and not scalable. Here, we establish a new protocol for small-scale production of HCAdV based on commercially available adenovirus purification systems and a standard method for the quality control of final HCAdV preparations. For titration of final vector preparations, we established a droplet digital polymerase chain reaction (ddPCR) that uses a standard free-end-point PCR in small droplets of defined volume. By using different probes, this method is capable of detecting and quantifying HCAdV and HV in one reaction independent of reference material, rendering this method attractive for accurately comparing viral titers between different laboratories. In summary, we demonstrate that it is possible to produce HCAdV in a small scale of sufficient quality and quantity to perform experiments in cell culture, and we established a reliable protocol for vector titration based on ddPCR. Our method significantly reduces time and required equipment to perform HCAdV production. In the future the ddPCR technology could be advantageous for titration of other viral vectors commonly used in gene therapy.

Optimization of Droplet Digital PCR from RNA and DNA extracts with direct comparison to RT-qPCR: Clinical implications for quantification of Oseltamivir-resistant subpopulations

The recent introduction of Droplet Digital PCR (ddPCR) has provided researchers with a tool that permits direct quantification of nucleic acids from a wide range of samples with increased precision and sensitivity versus RT-qPCR. The sample interdependence of RT-qPCR stemming from the measurement of Cq and ΔCq values is eliminated with ddPCR which provides an independent measure of the absolute nucleic acid concentration for each sample without standard curves thereby reducing inter-well and inter-plate variability. Well-characterized RNA purified from H275-wild type (WT) and H275Y-point mutated (MUT) neuraminidase of influenza A (H1N1) pandemic 2009 virus was used to demonstrate a ddPCR optimization workflow to assure robust data for downstream analysis. The ddPCR reaction mix was also tested with RT-qPCR and gave excellent reaction efficiency (between 90% and 100%) with the optimized MUT/WT duplexed assay thus enabling the direct comparison of the two platforms from the same reaction mix and thermal cycling protocol. ddPCR gave a marked improvement in sensitivity (>30-fold) for mutation abundance using a mixture of purified MUT and WT RNA and increased precision (>10 fold, p<0.05 for both inter- and intra-assay variability) versus RT-qPCR from patient samples to accurately identify residual mutant viral population during recovery.

Acute human herpesvirus-6A infection of human mesothelial cells modulates HLA molecules

Human herpesvirus 6A (HHV-6A) causes ubiquitous infections and has been associated with several diseases in immunosuppressed and immune dysregulated individuals. Although considered a lymphotropic virus, HHV-6A has the potential to infect many cell types, inducing important alterations in the infected cell. In our search for additional potential targets for HHV-6A infection, we analyzed the susceptibility of human mesothelial cells to viral infection. HHV-6A infection was performed and analyzed on primary human mesothelial cells isolated from serous cavity fluid, infected in vitro with a cell-free HHV-6A inoculum. The results demonstrated that mesothelial cells are susceptible to in vitro HHV-6A infection, and more importantly, that the virus induces an alteration of HLA expression on the cell surface, inducing HLA class II and HLA-G de novo expression. Since mesothelial cells play a pivotal role in many processes, including inflammation and antigen presentation, we speculate that, in vivo, this virus-induced perturbation might be correlated to alterations in mesothelium functions.

Optimisation of a quantitative polymerase chain reaction-based strategy for the detection and quantification of human herpesvirus 6 DNA in patients undergoing allogeneic haematopoietic stem cell transplantation

Human herpesvirus 6 (HHV-6) may cause severe complications after haematopoietic stem cell transplantation (HSCT). Monitoring this virus and providing precise, rapid and early diagnosis of related clinical diseases, constitute essential measures to improve outcomes. A prospective survey on the incidence and clinical features of HHV-6 infections after HSCT has not yet been conducted in Brazilian patients and the impact of this infection on HSCT outcome remains unclear. A rapid test based on real-time quantitative polymerase chain reaction (qPCR) has been optimised to screen and quantify clinical samples for HHV-6. The detection step was based on reaction with TaqMan^® hydrolysis probes. A set of previously described primers and probes have been tested to evaluate efficiency, sensitivity and reproducibility. The target efficiency range was 91.4% with linearity ranging from 10-10⁶ copies/reaction and a limit of detection of five copies/reaction or 250 copies/mL of plasma. The qPCR assay developed in the present study was simple, rapid and sensitive, allowing the detection of a wide range of HHV-6 loads. In conclusion, this test may be useful as a practical tool to help elucidate the clinical relevance of HHV-6 infection and reactivation in different scenarios and to determine the need for surveillance.

Laboratory and clinical aspects of human herpesvirus 6 infections

Human herpesvirus 6 (HHV-6) is a widespread betaherpesvirus which is genetically related to human cytomegalovirus (HCMV) and now encompasses two different species: HHV-6A and HHV-6B. HHV-6 exhibits a wide cell tropism in vivo and, like other herpesviruses, induces a lifelong latent infection in humans. As a noticeable difference with respect to other human herpesviruses, genomic HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6) in about 1% of the general population. Although it is infrequent, this may be a confounding factor for the diagnosis of active viral infection. The diagnosis of HHV-6 infection is performed by both serologic and direct methods. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time PCR. Many active HHV-6 infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. However, the virus may be the cause of serious diseases, particularly in immunocompromised individuals. As emblematic examples of HHV-6 pathogenicity, exanthema subitum, a benign disease of infancy, is associated with primary infection, whereas further virus reactivations can induce severe encephalitis cases, particularly in hematopoietic stem cell transplant recipients. Generally speaking, the formal demonstration of the causative role of HHV-6 in many acute and chronic human diseases is difficult due to the ubiquitous nature of the virus, chronicity of infection, existence of two distinct species, and limitations of current investigational tools. The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active HHV-6 infections, but the indications for treatment, as well as the conditions of drug administration, are not formally approved to date. There are still numerous pending questions about HHV-6 which should stimulate future research works on the pathophysiology, diagnosis, and therapy of this remarkable human virus.

Evidence linking HHV-6 with multiple sclerosis: an update

Following reports of elevated antiviral antibodies in MS patient sera and viral DNA detection in MS plaques nearly two decades ago, the neurovirology community has actively explored how herpesviruses such as HHV-6 might be involved in MS disease pathogenesis. Though findings across the field are non-uniform, an emerging consensus of viral correlates with disease course and evidence of HHV-6-specific immune responses in the CNS provide compelling evidence for a role, direct or indirect, of this virus in MS. Ultimately, the only way to demonstrate the involvement, or lack thereof, of HHV-6 or other herpesviruses in this disease is through a controlled clinical trial of an efficacious antiviral drug.

Germ-line transmitted, chromosomally integrated HHV-6 and classical Hodgkin lymphoma

A unique feature of both human herpesvirus 6A and B (HHV-6A and B) among human herpesviruses is their ability to integrate into chromosomal telomeres. In some individuals integrated viral genomes are present in the germ-line and result in the vertical transmission of HHV-6; however, little is known about the disease associations of germ-line transmitted, chromosomally integrated HHV-6 (ciHHV-6). Recent publications suggest that HHV-6 is associated with classical Hodgkin lymphoma (cHL). Here we examine the prevalence of ciHHV-6 in 936 cases of cHL and 563 controls by screening with a duplex TaqMan assay and confirming with droplet digital PCR. ciHHV-6 was detected in 10/563 (1.8%) controls and in all but one individual the virus was HHV-6B. Amongst cases 16/936 (1.7%) harboured ciHHV-6, thus demonstrating no association between ciHHV-6 and risk of cHL.

Past, present, and future perspectives on the diagnosis of Roseolovirus infections

Diagnosis of Roseolovirus infections mandates careful selection of patients, samples, and testing methods. We review advances in the field and highlight research priorities. Quantitative (q)PCR can accurately identify and distinguish between human herpesvirus 6 (HHV-6) species A and B. Whether screening of high-risk patients improves outcomes is unclear. Chromosomally integrated (ci)HHV-6 confounds test interpretation but can be ruled out with digital PCR. Reverse transcription qPCR may be a more specific and clinically applicable test for actively replicating Roseoloviruses, particularly among patients with ciHHV-6. Interpretation of Roseolovirus test results faces many challenges. However, careful application of refined and emerging diagnostic techniques will allow for increasingly accurate diagnosis of clinically significant infections and disease associations.