Varicella-zoster virus transcriptome in latently infected human ganglia

Variable Gene Expression in Human Ganglia Latently Infected with Varicella-Zoster Virus

Varicella-Zoster virus (VZV) is a pathogenic human herpes virus that causes varicella ("chicken pox") as a primary infection, following which it becomes latent in neuronal cells in human peripheral ganglia. It may then reactivate to cause herpes zoster ("shingles"). Defining the pattern of VZV gene expression during latency is an important issue, and four highly expressed VZV genes were first identified by Randall Cohrs in 1996 using cDNA libraries. Further studies from both his and other laboratories, including our own, have suggested that viral gene expression may be more widespread than previously thought, but a confounding factor has always been the possibility of viral reactivation after death in tissues obtained even at 24 h post-mortem. Recent important studies, which Randall Cohrs contributed to, have clarified this issue by studying human trigeminal ganglia at 6 h after death using RNA-Seq methodology when a novel spliced latency-associated VZV transcript (VLT) was found to be mapped antisense to the viral transactivator gene 61. Viral gene expression could be induced by a VLT-ORF 63 fusion transcript when VZV reactivated from latency. Prior detection by several groups of ORF63 in post-mortem-acquired TG is very likely to reflect detection of the VLT-ORF63 fusion and not canonical ORF63. The contributions to the VZV latency field by Randall Cohrs have been numerous and highly significant.

Trigeminal Trophic Syndrome: A Comprehensive Review of a Surgical Approach

ABSTRACT

Trigeminal trophic syndrome (TTS) is an exceedingly rare disease that causes facial ulceration, most commonly at the nasal ala. The overall incidence of TTS is not known, with less than 150 cases published in the literature.We searched the United States National Library of Medicine National Institutes of Health (PubMed) using the terms "Trigeminal Trophic Syndrome" and "TTS" as keywords. Publications in all languages were included if an English abstract was available. We reviewed 111 cases of TTS described in 75 publications from 1979 to 2021.Fourteen cases involved surgical reconstruction. Of these, the lesions completely healed in 7 cases (50%), recurred in 5 (36%), and were unspecified in 2 (14%). Reconstruction was completed in a 2 to 3-stage approach in 6 cases; of these, healing without recurrence was observed in 5 cases (83%). When donor tissue from the affected side was used as a basis for reconstruction, healing without recurrence was observed in 2 cases (50%). This is in comparison to the use of contralateral, sensate tissue in which there was healing without recurrence in all 3 cases (100%).The surgical management of TTS remains a topic of controversy. The rates of success remain comparable despite the use of various flap types. However, the use of contralateral, sensate flaps and a staged surgical approach appears to be effective based upon the best available evidence in the literature. Further prospective or retrospective controlled studies are necessary to make more reliable recommendations, though may be challenging given the rarity of TTS.

Varicella-pox virus infection: features of the course, clinical manifestations, complications, and possibilities for prevention

Varicella zoster virus (VZV) is a pathogenic human herpes virus that causes chickenpox as a primary infection, after which it persists for a long time and latently in the peripheral ganglia. Decades later, the virus can reactivate spontaneously, or after exposure to a number of triggering factors, causing herpes zoster (shingles). The reasons for the long-term persistence of VZV are gradually being revealed, but some issues remain unknown at the moment. Chickenpox and its complications are especially difficult in immunocompromised patients, but they are often found in people without risk factors. The most frequent and important complication of VZV reactivation is postherpetic neuralgia; encephalitis, segmental motor weakness and myelopathy, cranial neuropathies, and gastrointestinal complications often develop. The only scientifically proven effective and affordable way of mass prevention at the moment is vaccination. Chickenpox vaccines are safe and effective in preventing morbidity and mortality associated with the disease.

Recent Issues in Varicella-Zoster Virus Latency

Varicella-zoster virus (VZV) is a human herpes virus which causes varicella (chicken pox) as a primary infection, and, following a variable period of latency in neurons in the peripheral ganglia, may reactivate to cause herpes zoster (shingles) as well as a variety of neurological syndromes. In this overview we consider some recent issues in alphaherpesvirus latency with special focus on VZV ganglionic latency. A key question is the nature and extent of viral gene transcription during viral latency. While it is known that this is highly restricted, it is only recently that the very high degree of that restriction has been clarified, with both VZV gene 63-encoded transcripts and discovery of a novel VZV transcript (VLT) that maps antisense to the viral transactivator gene 61. It has also emerged in recent years that there is significant epigenetic regulation of VZV gene transcription, and the mechanisms underlying this are complex and being unraveled. The last few years has also seen an increased interest in the immunological aspects of VZV latency and reactivation, in particular from the perspective of inborn errors of host immunity that predispose to different VZV reactivation syndromes.

Varicella-Zoster Virus Infection of Neurons Derived from Neural Stem Cells

Varicella-Zoster virus (VZV) is a human herpesvirus that causes varicella (chickenpox) as a primary infection, and, following a variable period of ganglionic latency in neurons, it reactivates to cause herpes zoster (shingles). An analysis of VZV infection in cultures of neural cells, in particular when these have been obtained from induced pluripotent stem cells (iPSCs) or neural stem cells consisting of highly purified neuronal cultures, has revealed much data that may be of neurobiological significance. Early studies of VZV infection of mature cultured neural cells were mainly descriptive, but more recent studies in homogeneous neural stem cell cultures have used both neuronal cell markers and advanced molecular technology. Two general findings from such studies have been that (a) VZV infection of neurons is less severe, based on several criteria, than that observed in human fibroblasts, and (b) VZV infection of neurons does not lead to apoptosis in these cells in contrast to apoptosis observed in fibroblastic cells. Insights gained from such studies in human neural stem cells suggest that a less severe initial lytic infection in neurons, which are resistant to apoptosis, is likely to facilitate a pathological pathway to a latent state of the virus in human ganglia.

Current In Vitro Models to Study Varicella Zoster Virus Latency and Reactivation

Varicella zoster virus (VZV) is a highly prevalent human pathogen that causes varicella (chicken pox) during primary infection and establishes latency in peripheral neurons. Symptomatic reactivation often presents as zoster (shingles), but it has also been linked to life-threatening diseases such as encephalitis, vasculopathy and meningitis. Zoster may be followed by postherpetic neuralgia, neuropathic pain lasting after resolution of the rash. The mechanisms of varicella zoster virus (VZV) latency and reactivation are not well characterized. This is in part due to the human-specific nature of VZV that precludes the use of most animal and animal-derived neuronal models. Recently, in vitro models of VZV latency and reactivation using human neurons derived from stem cells have been established facilitating an understanding of the mechanisms leading to VZV latency and reactivation. From the models, c-Jun N-terminal kinase (JNK), phosphoinositide 3-kinase (PI3K) and nerve growth factor (NGF) have all been implicated as potential modulators of VZV latency/reactivation. Additionally, it was shown that the vaccine-strain of VZV is impaired for reactivation. These models may also aid in the generation of prophylactic and therapeutic strategies to treat VZV-associated pathologies. This review summarizes and analyzes the current human neuronal models used to study VZV latency and reactivation, and provides some strategies for their improvement.

Long-read sequencing uncovers a complex transcriptome topology in varicella zoster virus

BACKGROUND

Varicella zoster virus (VZV) is a human pathogenic alphaherpesvirus harboring a relatively large DNA molecule. The VZV transcriptome has already been analyzed by microarray and short-read sequencing analyses. However, both approaches have substantial limitations when used for structural characterization of transcript isoforms, even if supplemented with primer extension or other techniques. Among others, they are inefficient in distinguishing between embedded RNA molecules, transcript isoforms, including splice and length variants, as well as between alternative polycistronic transcripts. It has been demonstrated in several studies that long-read sequencing is able to circumvent these problems.

RESULTS

In this work, we report the analysis of the VZV lytic transcriptome using the Oxford Nanopore Technologies sequencing platform. These investigations have led to the identification of 114 novel transcripts, including mRNAs, non-coding RNAs, polycistronic RNAs and complex transcripts, as well as 10 novel spliced transcripts and 25 novel transcription start site isoforms and transcription end site isoforms. A novel class of transcripts, the nroRNAs are described in this study. These transcripts are encoded by the genomic region located in close vicinity to the viral replication origin. We also show that the ORF63 exhibits a complex structural variation encompassing the splice sites of VZV latency transcripts. Additionally, we have detected RNA editing in a novel non-coding RNA molecule.

CONCLUSIONS

Our investigations disclosed a composite transcriptomic architecture of VZV, including the discovery of novel RNA molecules and transcript isoforms, as well as a complex meshwork of transcriptional read-throughs and overlaps. The results represent a substantial advance in the annotation of the VZV transcriptome and in understanding the molecular biology of the herpesviruses in general.

Clinical Features of Varicella-Zoster Virus Infection

Varicella-zoster virus (VZV) is a pathogenic human herpes virus that causes varicella (chickenpox) as a primary infection, following which it becomes latent in peripheral ganglia. Decades later, the virus may reactivate either spontaneously or after a number of triggering factors to cause herpes zoster (shingles). Varicella and its complications are more severe in the immunosuppressed. The most frequent and important complication of VZV reactivation is postherpetic neuralgia, the cause of which is unknown and for which treatment is usually ineffective. Reactivation of VZV may also cause a wide variety of neurological syndromes, the most significant of which is a vasculitis, which is treated with corticosteroids and the antiviral drug acyclovir. Other VZV reactivation complications include an encephalitis, segmental motor weakness and myelopathy, cranial neuropathies, Guillain–Barré syndrome, enteric features, and zoster sine herpete, in which the viral reactivation occurs in the absence of the characteristic dermatomally distributed vesicular rash of herpes zoster. There has also been a recent association of VZV with giant cell arteritis and this interesting finding needs further corroboration. Vaccination is now available for the prevention of both varicella in children and herpes zoster in older individuals.

Adenoviromics: Mining the Human Adenovirus Species D Genome

Human adenovirus (HAdV) infections cause disease world-wide. Whole genome sequencing has now distinguished 90 distinct genotypes in 7 species (A-G). Over half of these 90 HAdVs fall within species D, with essentially all of the HAdV-D whole genome sequences generated in the last decade. Herein, we describe recent new findings made possible by mining of this expanded genome database, and propose future directions to elucidate new functional elements and new functions for previously known viral components.

A Single-Cell Approach to the Elusive Latent Human Cytomegalovirus Transcriptome

Herpesvirus latency has been difficult to understand molecularly due to low levels of viral genomes and gene expression. In the case of the betaherpesvirus human cytomegalovirus (HCMV), this is further complicated by the heterogeneity inherent to hematopoietic subpopulations harboring genomes and, as a consequence, the various patterns of infection that simultaneously exist in a host, ranging from latent to lytic. Single-cell RNA sequencing (scRNA-seq) provides tremendous potential in measuring the gene expression profiles of heterogeneous cell populations for a wide range of applications, including in studies of cancer, immunology, and infectious disease. A recent study by Shnayder et al. (mBio 9:e00013-18, 2018, https://doi.org/10.1128/mBio.00013-18) utilized scRNA-seq to define transcriptomal characteristics of HCMV latency. They conclude that latency-associated gene expression is similar to the late lytic viral program but at lower levels of expression. The study highlights the numerous challenges, from the definition of latency to the analysis of scRNA-seq, that exist in defining a latent transcriptome.

A spliced latency-associated VZV transcript maps antisense to the viral transactivator gene 61

Varicella-zoster virus (VZV), an alphaherpesvirus, establishes lifelong latent infection in the neurons of >90% humans worldwide, reactivating in one-third to cause shingles, debilitating pain and stroke. How VZV maintains latency remains unclear. Here, using ultra-deep virus-enriched RNA sequencing of latently infected human trigeminal ganglia (TG), we demonstrate the consistent expression of a spliced VZV mRNA, antisense to VZV open reading frame 61 (ORF61). The spliced VZV latency-associated transcript (VLT) is expressed in human TG neurons and encodes a protein with late kinetics in productively infected cells in vitro and in shingles skin lesions. Whereas multiple alternatively spliced VLT isoforms (VLT_ly) are expressed during lytic infection, a single unique VLT isoform, which specifically suppresses ORF61 gene expression in co-transfected cells, predominates in latently VZV-infected human TG. The discovery of VLT links VZV with the other better characterized human and animal neurotropic alphaherpesviruses and provides insights into VZV latency.

Varicella-zoster virus (VZV) establishes lifelong infection in the majority of the population, but mechanisms underlying latency remain unclear. Here, the authors use ultra-deep RNA sequencing, enriched for viral RNAs, of latently infected human trigeminal ganglia and identify a spliced, latency-associated VZV mRNA.

Transcriptome-wide characterization of human cytomegalovirus in natural infection and experimental latency

The transcriptional program associated with herpesvirus latency and the viral genes regulating entry into and exit from latency are poorly understood and controversial. Here, we developed and validated a targeted enrichment platform and conducted large-scale transcriptome analyses of human cytomegalovirus (HCMV) infection. We used both an experimental hematopoietic cell model of latency and cells from naturally infected, healthy human subjects (clinical) to define the breadth of viral genes expressed. The viral transcriptome derived from experimental infection was highly correlated with that from clinical infection, validating our experimental latency model. These transcriptomes revealed a broader profile of gene expression during infection in hematopoietic cells than previously appreciated. Further, using recombinant viruses that establish a nonreactivating, latent-like or a replicative infection in CD34⁺ hematopoietic progenitor cells, we defined classes of low to moderately expressed genes that are differentially regulated in latent vs. replicative states of infection. Most of these genes have yet to be studied in depth. By contrast, genes that were highly expressed, were expressed similarly in both latent and replicative infection. From these findings, a model emerges whereby low or moderately expressed genes may have the greatest impact on regulating the switch between viral latency and replication. The core set of viral genes expressed in natural infection and differentially regulated depending on the pattern of infection provides insight into the HCMV transcriptome associated with latency in the host and a resource for investigating virus-host interactions underlying persistence.

Targeted Genome Sequencing Reveals Varicella-Zoster Virus Open Reading Frame 12 Deletion

The neurotropic herpesvirus varicella-zoster virus (VZV) establishes a lifelong latent infection in humans following primary infection. The low abundance of VZV nucleic acids in human neurons has hindered an understanding of the mechanisms that regulate viral gene transcription during latency. To overcome this critical barrier, we optimized a targeted capture protocol to enrich VZV DNA and cDNA prior to whole-genome/transcriptome sequence analysis. Since the VZV genome is remarkably stable, it was surprising to detect that VZV32, a VZV laboratory strain with no discernible growth defect in tissue culture, contained a 2,158-bp deletion in open reading frame (ORF) 12. Consequently, ORF 12 and 13 protein expression was abolished and Akt phosphorylation was inhibited. The discovery of the ORF 12 deletion, revealed through targeted genome sequencing analysis, points to the need to authenticate the VZV genome when the virus is propagated in tissue culture.IMPORTANCE Viruses isolated from clinical samples often undergo genetic modifications when cultured in the laboratory. Historically, VZV is among the most genetically stable herpesviruses, a notion supported by more than 60 complete genome sequences from multiple isolates and following multiple in vitro passages. However, application of enrichment protocols to targeted genome sequencing revealed the unexpected deletion of a significant portion of VZV ORF 12 following propagation in cultured human fibroblast cells. While the enrichment protocol did not introduce bias in either the virus genome or transcriptome, the findings indicate the need for authentication of VZV by sequencing when the virus is propagated in tissue culture.

Inborn errors in RNA polymerase III underlie severe varicella zoster virus infections

Varicella zoster virus (VZV) typically causes chickenpox upon primary infection. In rare cases, VZV can give rise to life-threatening disease in otherwise healthy people, but the immunological basis for this remains unexplained. We report 4 cases of acute severe VZV infection affecting the central nervous system or the lungs in unrelated, otherwise healthy children who are heterozygous for rare missense mutations in POLR3A (one patient), POLR3C (one patient), or both (two patients). POLR3A and POLR3C encode subunits of RNA polymerase III. Leukocytes from all 4 patients tested exhibited poor IFN induction in response to synthetic or VZV-derived DNA. Moreover, leukocytes from 3 of the patients displayed defective IFN production upon VZV infection and reduced control of VZV replication. These phenotypes were rescued by transduction with relevant WT alleles. This work demonstrates that monogenic or digenic POLR3A and POLR3C deficiencies confer increased susceptibility to severe VZV disease in otherwise healthy children, providing evidence for an essential role of a DNA sensor in human immunity.

Human Cytomegalovirus Latency: Approaching the Gordian Knot

Herpesviruses have evolved exquisite virus-host interactions that co-opt or evade a number of host pathways to enable the viruses to persist. Persistence of human cytomegalovirus (CMV), the prototypical betaherpesvirus, is particularly complex in the host organism. Depending on host physiology and the cell types infected, CMV persistence comprises latent, chronic, and productive states that may occur concurrently. Viral latency is a central strategy by which herpesviruses ensure their lifelong persistence. Although much remains to be defined about the virus-host interactions important to CMV latency, it is clear that checkpoints composed of viral and cellular factors exist to either maintain a latent state or initiate productive replication in response to host cues. CMV offers a rich platform for defining the virus-host interactions and understanding the host biology important to viral latency. This review describes current understanding of the virus-host interactions that contribute to viral latency and reactivation.

Issues in the Treatment of Neurological Conditions Caused by Reactivation of Varicella Zoster Virus (VZV)

Varicella zoster virus (VZV) is a ubiquitous neurotropic human herpesvirus. Primary infection usually causes varicella (chicken pox), after which virus becomes latent in ganglia along the entire neuraxis. Decades later, virus reactivates to produce herpes zoster (shingles), a painful dermatomally distributed vesicular eruption. Zoster may be further complicated by postherpetic neuralgia, VZV vasculopathy, myelitis, and segmental motor weakness. VZV reactivation has also been associated with giant cell arteritis. This overview discusses treatment of various conditions that often require both corticosteroids and antiviral drugs. Treatment for VZV-associated disease is often based on case reports and small studies rather than large-scale clinical trials. Issues that require resolution include the optimal duration of such combined therapy, more effective treatment for postherpetic neuralgia, whether some treatments should be given orally or intravenously, the widening spectrum of zoster sine herpete, and the role of antiviral therapy in giant cell arteritis.

Alphaherpesvirus DNA replication in dissociated human trigeminal ganglia

Analysis of the frequency and PCR-quantifiable abundance of herpes simplex virus type 1 (HSV-1) and varicella zoster virus (VZV) DNA in multiple biological replicates of cells from dissociated randomly distributed human trigeminal ganglia (TG) of four subjects revealed an increase in both parameters and in both viruses during 5 days of culture, with no further change by 10 days. Dissociated TG provides a platform to analyze initiation of latent virus DNA replication within 5 days of culture.

Varicella Zoster Virus in the Nervous System

Varicella zoster virus (VZV) is a ubiquitous, exclusively human alphaherpesvirus. Primary infection usually results in varicella (chickenpox), after which VZV becomes latent in ganglionic neurons along the entire neuraxis. As VZV-specific cell-mediated immunity declines in elderly and immunocompromised individuals, VZV reactivates and causes herpes zoster (shingles), frequently complicated by postherpetic neuralgia. VZV reactivation also produces multiple serious neurological and ocular diseases, such as cranial nerve palsies, meningoencephalitis, myelopathy, and VZV vasculopathy, including giant cell arteritis, with or without associated rash. Herein, we review the clinical, laboratory, imaging, and pathological features of neurological complications of VZV reactivation as well as diagnostic tests to verify VZV infection of the nervous system. Updates on the physical state of VZV DNA and viral gene expression in latently infected ganglia, neuronal, and primate models to study varicella pathogenesis and immunity are presented along with innovations in the immunization of elderly individuals to prevent VZV reactivation.

Differential regulation of matrix metalloproteinases in varicella zoster virus-infected human brain vascular adventitial fibroblasts

Upon reactivation, varicella zoster virus (VZV) spreads transaxonally, infects cerebral arteries and causes ischemic or hemorrhagic stroke, as well as aneurysms. The mechanism(s) of VZV-induced aneurysm formation is unknown. However, matrix metalloproteinases (MMPs), which digest extracellular structural proteins in the artery wall, play a role in cerebral and aortic artery aneurysm formation and rupture. Here, we examined the effect of VZV infection on expression of MMP-1, -2, -3, and -9 in primary human brain vascular adventitial fibroblasts (BRAFS). At 6 days post-infection, VZV- and mock-infected BRAFs were analyzed for mRNA levels of MMP-1, -2, -3 and -9 by RT-PCR and for corresponding total intra- and extracellular protein levels by multiplex ELISA. The activity of MMP-1 was also measured in a substrate cleavage assay. Compared to mock-infected BRAFs, MMP-1, MMP-3 and MMP-9 transcripts, cell lysate protein and conditioned supernatant protein were all increased in VZV-infected BRAFs, whereas MMP-2 transcripts, cell lysate protein and conditioned supernatant protein were decreased. MMP-1 from the conditioned supernatant of VZV-infected BRAFs showed increased cleavage activity on an MMP-1-specific substrate compared to mock-infected BRAFs. Differential regulation of MMPs in VZV-infected BRAFs may contribute to aneurysm formation in VZV vasculopathy.

Burning mouth syndrome due to herpes simplex virus type 1

Burning mouth syndrome is characterised by chronic orofacial burning pain. No dental or medical cause has been found. We present a case of burning mouth syndrome of 6 months duration in a healthy 65-year-old woman, which was associated with high copy numbers of herpes simplex virus type 1 (HSV-1) DNA in the saliva. Her pain resolved completely after antiviral treatment with a corresponding absence of salivary HSV-1 DNA 4 weeks and 6 months later.

A comparison of herpes simplex virus type 1 and varicella-zoster virus latency and reactivation

Herpes simplex virus type 1 (HSV-1; human herpesvirus 1) and varicella-zoster virus (VZV; human herpesvirus 3) are human neurotropic alphaherpesviruses that cause lifelong infections in ganglia. Following primary infection and establishment of latency, HSV-1 reactivation typically results in herpes labialis (cold sores), but can occur frequently elsewhere on the body at the site of primary infection (e.g. whitlow), particularly at the genitals. Rarely, HSV-1 reactivation can cause encephalitis; however, a third of the cases of HSV-1 encephalitis are associated with HSV-1 primary infection. Primary VZV infection causes varicella (chickenpox) following which latent virus may reactivate decades later to produce herpes zoster (shingles), as well as an increasingly recognized number of subacute, acute and chronic neurological conditions. Following primary infection, both viruses establish a latent infection in neuronal cells in human peripheral ganglia. However, the detailed mechanisms of viral latency and reactivation have yet to be unravelled. In both cases latent viral DNA exists in an 'end-less' state where the ends of the virus genome are joined to form structures consistent with unit length episomes and concatemers, from which viral gene transcription is restricted. In latently infected ganglia, the most abundantly detected HSV-1 RNAs are the spliced products originating from the primary latency associated transcript (LAT). This primary LAT is an 8.3 kb unstable transcript from which two stable (1.5 and 2.0 kb) introns are spliced. Transcripts mapping to 12 VZV genes have been detected in human ganglia removed at autopsy; however, it is difficult to ascribe these as transcripts present during latent infection as early-stage virus reactivation may have transpired in the post-mortem time period in the ganglia. Nonetheless, low-level transcription of VZV ORF63 has been repeatedly detected in multiple ganglia removed as close to death as possible. There is increasing evidence that HSV-1 and VZV latency is epigenetically regulated. In vitro models that permit pathway analysis and identification of both epigenetic modulations and global transcriptional mechanisms of HSV-1 and VZV latency hold much promise for our future understanding in this complex area. This review summarizes the molecular biology of HSV-1 and VZV latency and reactivation, and also presents future directions for study.

Pathogenesis of varicelloviruses in primates

Varicelloviruses in primates comprise the prototypic human varicella-zoster virus (VZV) and its non-human primate homologue, simian varicella virus (SVV). Both viruses cause varicella as a primary infection, establish latency in ganglionic neurons and reactivate later in life to cause herpes zoster in their respective hosts. VZV is endemic worldwide and, although varicella is usually a benign disease in childhood, VZV reactivation is a significant cause of neurological disease in the elderly and in immunocompromised individuals. The pathogenesis of VZV infection remains ill-defined, mostly due to the species restriction of VZV that impedes studies in experimental animal models. SVV infection of non-human primates parallels virological, clinical, pathological and immunological features of human VZV infection, thereby providing an excellent model to study the pathogenesis of varicella and herpes zoster in its natural host. In this review, we discuss recent studies that provided novel insight in both the virus and host factors involved in the three elementary stages of Varicellovirus infection in primates: primary infection, latency and reactivation.

Viruses, apoptosis, and neuroinflammation--a double-edged sword

Apoptosis, or programmed cell death, is a fundamental and widespread cell biological process that is distinct from cell necrosis and can be induced by a wide variety of stimuli including viral infections. Apoptosis may occur via either the intrinsic or extrinsic pathways and confers several advantages to the virally infected host including the prevention of further viral propagation and the potential inhibition and resolution of inflammatory processes. Several viruses have been shown to have the capacity to induce apoptosis in susceptible cells including herpes simplex virus, Varicella-zoster virus, rabies virus, human immunodeficiency virus, and reovirus. Apoptosis has also been observed in human African trypanosomiasis which is an infection caused by a protozoan parasite. The mechanisms leading to apoptosis may differ depending on the type of infection. Apoptosis has been reported in several neurodegenerative diseases and also psychiatric disorders but the true clinical significance of such observations is not certain, and, though interesting, it is very difficult to ascribe causation in these conditions. The presence of inflammation in the central nervous system in any neurological condition, including those associated with a viral infection, is not necessarily an absolute marker of serious disease and the notion of 'good' versus 'bad' inflammation is considered to be valid in some circumstances. The precise relationship between viruses, apoptosis, and inflammation is viewed as a complex one requiring further investigation to unravel and understand its nature.

Rates of vaccine evolution show strong effects of latency: implications for varicella zoster virus epidemiology

Varicella-zoster virus (VZV) causes chickenpox and shingles, and is found in human populations worldwide. The lack of temporal signal in the diversity of VZV makes substitution rate estimates unreliable, which is a barrier to understanding the context of its global spread. Here, we estimate rates of evolution by studying live attenuated vaccines, which evolved in 22 vaccinated patients for known periods of time, sometimes, but not always undergoing latency. We show that the attenuated virus evolves rapidly (∼ 10(-6) substitutions/site/day), but that rates decrease dramatically when the virus undergoes latency. These data are best explained by a model in which viral populations evolve for around 13 days before becoming latent, but then undergo no replication during latency. This implies that rates of viral evolution will depend strongly on transmission patterns. Nevertheless, we show that implausibly long latency periods are required to date the most recent common ancestor of extant VZV to an "out-of-Africa" migration with humans, as has been previously suggested.

Infected peripheral blood mononuclear cells transmit latent varicella zoster virus infection to the guinea pig enteric nervous system

Latent wild-type (WT) and vaccine (vOka) varicella zoster virus (VZV) are found in the human enteric nervous system (ENS). VZV also infects guinea pig enteric neurons in vitro, establishes latency and can be reactivated. We therefore determined whether lymphocytes infected in vitro with VZV secrete infectious virions and can transfer infection in vivo to the ENS of recipient guinea pigs. T lymphocytes (CD3-immunoreactive) were preferentially infected following co-culture of guinea pig or human peripheral blood mononuclear cells with VZV-infected HELF. VZV proliferated in the infected T cells and expressed immediate early and late VZV genes. Electron microscopy confirmed that VZV-infected T cells produced encapsulated virions. Extracellular virus, however, was pleomorphic, suggesting degradation occurred prior to release, which was confirmed by the failure of VZV-infected T cells to secrete infectious virions. Intravenous injection of WT- or vOka-infected PBMCs, nevertheless, transmitted VZV to recipient animals (guinea pig > human lymphocytes). Two days post-inoculation, lung and liver, but not gut, contained DNA and transcripts encoding ORFs 4, 40, 66 and 67. Twenty-eight days after infection, gut contained DNA and transcripts encoding ORFs 4 and 66 but neither DNA nor transcripts could any longer be found in lung or liver. In situ hybridization revealed VZV DNA in enteric neurons, which also expressed ORF63p (but not ORF68p) immunoreactivity. Observations suggest that VZV infects T cells, which can transfer VZV to and establish latency in enteric neurons in vivo. Guinea pigs may be useful for studies of VZV pathogenesis in the ENS.

Inhibition of phosphorylated-STAT1 nuclear translocation and antiviral protein expression in human brain vascular adventitial fibroblasts infected with varicella-zoster virus

In varicella-zoster virus (VZV)-infected primary human brain vascular adventitial fibroblasts (BRAFs), levels of beta interferon (IFN-β,) STAT1, and STAT2 transcripts as well as STAT1 and STAT2 protein were decreased. IFN-α transcript levels were increased but not secreted IFN-α protein levels. Compared to IFN-α-treated control results, in VZV-infected BRAFs, phosphorylated STAT1 did not translocate to the nucleus, resulting in impaired downstream expression of interferon-inducible antiviral Mx1. Overall, VZV interference with the type I interferon pathway may promote virus persistence in cerebral arteries.

Frequency and abundance of alphaherpesvirus DNA in human thoracic sympathetic ganglia

Alphaherpesvirus reactivation from thoracic sympathetic ganglia (TSG) and transaxonal spread to target organs cause human visceral disease. Yet alphaherpesvirus latency in TSG has not been well characterized. In this study, quantitative PCR detected varicella-zoster virus (VZV), herpes simplex virus 1 (HSV-1), and HSV-2 DNA in 117 fresh TSG obtained postmortem from 15 subjects. VZV DNA was found in 76 (65%) ganglia from all subjects, HSV-1 DNA was found in 5 (4%) ganglia from 3 subjects, and no HSV-2 was found.

Clinical and molecular aspects of the live attenuated Oka varicella vaccine

VZV is a ubiquitous member of the Herpesviridae family that causes varicella (chicken pox) and herpes zoster (shingles). Both manifestations can cause great morbidity and mortality and are therefore of significant economic burden. The introduction of varicella vaccination as part of childhood immunization programs has resulted in a remarkable decline in varicella incidence, and associated hospitalizations and deaths, particularly in the USA. The vaccine preparation, vOka, is a live attenuated virus produced by serial passage of a wild-type clinical isolate termed pOka in human and guinea pig cell lines. Although vOka is clinically attenuated, it can cause mild varicella, establish latency, and reactivate to cause herpes zoster. Sequence analysis has shown that vOka differs from pOka by at least 42 loci; however, not all genomes possess the novel vOka change at all positions, creating a heterogeneous population of genetically distinct haplotypes. This, together with the extreme cell-associated nature of VZV replication in cell culture and the lack of an animal model, in which the complete VZV life cycle can be replicated, has limited studies into the molecular basis for vOka attenuation. Comparative studies of vOka with pOka replication in T cells, dorsal root ganglia, and skin indicate that attenuation likely involves multiple mutations within ORF 62 and several other genes. This article presents an overview of the clinical aspects of the vaccine and current progress on understanding the molecular mechanisms that account for the clinical phenotype of reduced virulence.

Comparison of varicella-zoster virus RNA sequences in human neurons and fibroblasts

Varicella-zoster virus (VZV) infection causes varicella, after which the virus becomes latent in ganglionic neurons. In tissue culture, VZV-infected human neurons remain viable at 2 weeks, whereas fibroblasts develop cytopathology. Next-generation RNA sequencing was used to compare VZV transcriptomes in neurons and fibroblasts and identified only 12 differentially transcribed genes of the 70 annotated VZV open reading frames (ORFs), suggesting that defective virus transcription does not account for the lack of cell death in VZV-infected neurons in vitro.

Molecular mechanisms of varicella zoster virus pathogenesis

Varicella zoster virus (VZV) is the causative agent of varicella (chickenpox) and zoster (shingles). Investigating VZV pathogenesis is challenging as VZV is a human-specific virus and infection does not occur, or is highly restricted, in other species. However, the use of human tissue xenografts in mice with severe combined immunodeficiency (SCID) enables the analysis of VZV infection in differentiated human cells in their typical tissue microenvironment. Xenografts of human skin, dorsal root ganglia or foetal thymus that contains T cells can be infected with mutant viruses or in the presence of inhibitors of viral or cellular functions to assess the molecular mechanisms of VZV-host interactions. In this Review, we discuss how these models have improved our understanding of VZV pathogenesis.

Influence of frequent infectious exposures on general and varicella-zoster virus-specific immune responses in pediatricians

Reexposure to viruses is assumed to strengthen humoral and cellular immunity via the secondary immune response. We studied the effects of frequent exposure to viral infectious challenges on immunity. Furthermore, we assessed whether repetitive exposures to varicella-zoster virus (VZV) elicited persistently high immune responses. Blood samples from 11 pediatricians and matched controls were assessed at 3 time points and 1 time point, respectively. Besides the assessment of general immunity by means of measuring T-cell subset percentages, antibody titers and gamma interferon (IFN-γ)/interleukin 2 (IL-2)-producing T-cell percentages against adenovirus type 5 (AdV-5), cytomegalovirus (CMV), tetanus toxin (TT), and VZV were determined. Pediatricians had lower levels of circulating CD4(+)-naive T cells and showed boosting of CD8(+) effector memory T cells. Although no effect on humoral immunity was seen, repetitive exposures to VZV induced persistently higher percentages of IFN-γ-positive T cells against all VZV antigens tested (VZV glycoprotein E [gE], VZV intermediate-early protein 62 [IE62], and VZV IE63) than in controls. T cells directed against latency-associated VZV IE63 benefitted the most from natural exogenous boosting. Although no differences in cellular or humoral immunity were found between the pediatricians and controls for AdV-5 or TT, we did find larger immune responses against CMV antigens in pediatricians. Despite the high infectious burden, we detected a robust and diverse immune system in pediatricians. Repetitive exposures to VZV have been shown to induce a stable increased level of VZV-specific cellular but not humoral immunity. Based on our observations, VZV IE63 can be considered a candidate for a zoster vaccine.

Varicella zoster virus (VZV)-human neuron interaction

Varicella zoster virus (VZV) is a highly neurotropic, exclusively human herpesvirus. Primary infection causes varicella (chickenpox), wherein VZV replicates in multiple organs, particularly the skin. Widespread infection in vivo is confirmed by the ability of VZV to kill tissue culture cells in vitro derived from any organ. After varicella, VZV becomes latent in ganglionic neurons along the entire neuraxis. During latency, virus DNA replication stops, transcription is restricted, and no progeny virions are produced, indicating a unique virus-cell (neuron) relationship. VZV reactivation produces zoster (shingles), often complicated by serious neurological and ocular disorders. The molecular trigger(s) for reactivation, and thus the identity of a potential target to prevent it, remains unknown due to an incomplete understanding of the VZV-neuron interaction. While no in vitro system has yet recapitulated the findings in latently infected ganglia, recent studies show that VZV infection of human neurons in SCID mice and of human stem cells, including induced human pluripotent stem cells and normal human neural progenitor tissue-like assemblies, can be established in the absence of a cytopathic effect. Usefulness of these systems in discovering the mechanisms underlying reactivation awaits analyses of VZV-infected, highly pure (>90%), terminally differentiated human neurons capable of prolonged survival in vitro.

The variegate neurological manifestations of varicella zoster virus infection

Varicella zoster virus (VZV) is an exclusively human neurotropic alphaherpesvirus. Primary infection causes varicella (chickenpox), after which the virus becomes latent in ganglionic neurons along the entire neuraxis. With advancing age or immunosuppression, cell-mediated immunity to VZV declines, and the virus reactivates to cause zoster (shingles), dermatomal distribution, pain, and rash. Zoster is often followed by chronic pain (postherpetic neuralgia), cranial nerve palsies, zoster paresis, vasculopathy, meningoencephalitis, and multiple ocular disorders. This review covers clinical, laboratory, and pathological features of neurological complications of VZV reactivation, including diagnostic testing to verify active VZV infection in the nervous system. Additional perspectives are provided by discussions of VZV latency, animal models to study varicella pathogenesis and immunity, and of the value of vaccination of elderly individuals to boost cell-mediated immunity to VZV and prevent VZV reactivation.

Three-dimensional normal human neural progenitor tissue-like assemblies: a model of persistent varicella-zoster virus infection

Varicella-zoster virus (VZV) is a neurotropic human alphaherpesvirus that causes varicella upon primary infection, establishes latency in multiple ganglionic neurons, and can reactivate to cause zoster. Live attenuated VZV vaccines are available; however, they can also establish latent infections and reactivate. Studies of VZV latency have been limited to the analyses of human ganglia removed at autopsy, as the virus is strictly a human pathogen. Recently, terminally differentiated human neurons have received much attention as a means to study the interaction between VZV and human neurons; however, the short life-span of these cells in culture has limited their application. Herein, we describe the construction of a model of normal human neural progenitor cells (NHNP) in tissue-like assemblies (TLAs), which can be successfully maintained for at least 180 days in three-dimensional (3D) culture, and exhibit an expression profile similar to that of human trigeminal ganglia. Infection of NHNP TLAs with cell-free VZV resulted in a persistent infection that was maintained for three months, during which the virus genome remained stable. Immediate-early, early and late VZV genes were transcribed, and low-levels of infectious VZV were recurrently detected in the culture supernatant. Our data suggest that NHNP TLAs are an effective system to investigate long-term interactions of VZV with complex assemblies of human neuronal cells.

Varicella-zoster virus (VZV), the alphaherpesvirus that typically causes childhood chickenpox and shingles in adults, becomes latent in neurons, thus remaining in the body for a lifetime. Unfortunately, few models are available to study the establishment of VZV latency since the virus infects only humans and establishes persistent infections and latency only in neurons, a slowly proliferating, short-lived cell in culture. We have successfully maintained normal human neural progenitor cells (NHNP) in tissue-like assemblies (TLAs) in 3-dimensional (3D) cultures for up to 6 months. The 3D NHNP TLAs show some characteristics as those found in the human trigeminal ganglia, the site of VZV latency. NHNP TLAs infected with VZV remain viable for 3 months during which time VZV DNA replicates and remains genetically stable, virus genes are transcribed, and infectious VZV is sporadically released. The ability to maintain VZV infected NHNP cells in culture for extended times provides the unique opportunity to study the molecular interactions between this important human pathogen and neuronal tissue to an extent previously unattainable.

GeXPS multiplex PCR analysis of the simian varicella virus transcriptome in productively infected cells in culture and acutely infected ganglia

Simian varicella zoster virus (SVV) infection of non-human primates serves as a model to study varicella zoster virus (VZV) infection and pathogenesis in humans. While macroarray analysis detected all 69 predicted unique open reading frames (ORFs) in SVV-infected cells in culture, it lacked the sensitivity to detect the low-abundance transcripts expressed in latently infected monkey ganglia. Recently, a multiplex RT-PCR assay using the GenomeLab Genetic Analysis System (GeXPS) identified 10 VZV transcripts in latently-infected human ganglia. GeXPS was used to analyze the SVV transcriptome in SVV-infected monkey cells in culture as well as in acutely infected ganglia from African green monkeys. Oligonucleotide primers containing both SVV ORF- and cell-specific sequences linked to universal DNA sequences were used in RT-PCR to produce products of predetermined sizes. Amplification products were resolved by capillary gel electrophoresis and detected by fluorescence spectrophotometry. Transcripts corresponding to all 69 predicted SVV ORFs, in addition to transcripts within the leftward end region and ORF 61 antisense transcripts were detected in virus-infected cells in culture. Except for two transcripts (ORFs 14 and 35), all transcripts found in infected tissue culture cells were also found in acutely infected monkey ganglia.

Age and immune status of rhesus macaques impact simian varicella virus gene expression in sensory ganglia

Simian varicella virus (SVV) infection of rhesus macaques (RMs) recapitulates the hallmarks of varicella-zoster virus (VZV) infection of humans, including the establishment of latency within the sensory ganglia. Various factors, including age and immune fitness, influence the outcome of primary VZV infection, as well as reactivation resulting in herpes zoster (HZ). To increase our understanding of the role of lymphocyte subsets in the establishment of viral latency, we analyzed the latent SVV transcriptome in juvenile RMs depleted of CD4 T, CD8 T, or CD20 B lymphocytes during acute infection. We have previously shown that SVV latency in sensory ganglia of nondepleted juvenile RMs is associated with a limited transcriptional profile. In contrast, CD4 depletion during primary infection resulted in the failure to establish a characteristic latent viral transcription profile in sensory ganglia, where we detected 68 out of 69 SVV-encoded open reading frames (ORFs). CD-depleted RMs displayed a latent transcriptional profile that included additional viral transcripts within the core region of the genome not detected in control RMs. The latent transcriptome of CD20-depleted RMs was comparable to the latent transcription in the sensory ganglia of control RMs. Lastly, we investigated the impact of age on the establishment of SVV latency. SVV gene expression was more active in ganglia from two aged RMs than in ganglia from juvenile RMs, with 25 of 69 SVV transcripts detected. Therefore, immune fitness at the time of infection modulates the establishment and/or maintenance of SVV latency.

Animal models of varicella zoster virus infection

Primary infection with varicella zoster virus (VZV) results in varicella (chickenpox) followed by the establishment of latency in sensory ganglia. Declining T cell immunity due to aging or immune suppressive treatments can lead to VZV reactivation and the development of herpes zoster (HZ, shingles). HZ is often associated with significant morbidity and occasionally mortality in elderly and immune compromised patients. There are currently two FDA-approved vaccines for the prevention of VZV: Varivax® (for varicella) and Zostavax® (for HZ). Both vaccines contain the live-attenuated Oka strain of VZV. Although highly immunogenic, a two-dose regimen is required to achieve a 99% seroconversion rate. Zostavax vaccination reduces the incidence of HZ by 51% within a 3-year period, but a significant reduction in vaccine-induced immunity is observed within the first year after vaccination. Developing more efficacious vaccines and therapeutics requires a better understanding of the host response to VZV. These studies have been hampered by the scarcity of animal models that recapitulate all aspects of VZV infections in humans. In this review, we describe different animal models of VZV infection as well as an alternative animal model that leverages the infection of Old World macaques with the highly related simian varicella virus (SVV) and discuss their contributions to our understanding of pathogenesis and immunity during VZV infection.

The challenging patient with varicella-zoster virus disease

Varicella-zoster virus (VZV) reactivation from latently infected ganglia causes multiple neurologic diseases. The most common is herpes zoster, which is frequently complicated by postherpetic neuralgia, meningoencephalitis, and vasculopathy, including VZV temporal arteritis, myelopathy, and retinal necrosis. All of these disorders can develop without rash. Importantly, VZV vasculopathy is emerging as a significant cause of TIAs and stroke. In particular, a subset of patients who present with symptoms and signs of giant cell arteritis (GCA), but whose temporal artery biopsies are GCA-negative, have multifocal VZV vasculopathy with temporal artery infection. Herein we focus on the specific diagnostic and therapeutic challenges that clinical neurologists encounter in diseases caused by VZV, discuss guidelines for zoster vaccine, and highlight molecular features of VZV latency with a focus on preventing the serious neurologic and ocular complications of VZV reactivation.

Human trigeminal ganglionic explants as a model to study alphaherpesvirus reactivation

Varicella zoster virus (VZV) latency is characterized by limited virus gene expression and the absence of virus DNA replication. Investigations of VZV latency and reactivation have been hindered by the lack of an in vitro model of virus latency. Since VZV is an exclusively human pathogen, we used naturally infected human trigeminal ganglia (TG) obtained at autopsy to study virus latency. Herein, we report optimization of medium to maintain TG integrity as determined by histology and immunohistochemistry. Using the optimized culture medium, we also found that both herpes simplex virus-1 (HSV-1) and VZV DNA replicated in TG explants after 5 days in culture. The increase in HSV-1 DNA was fourfold greater than the increase in VZV DNA. Overall, we present a model for alphaherpesvirus latency in human neurons in which the key molecular events leading to virus reactivation can be studied.

Restricted varicella-zoster virus transcription in human trigeminal ganglia obtained soon after death

We analyzed the varicella-zoster virus (VZV) transcriptome in 43 latently infected human trigeminal ganglia (TG) with postmortem intervals (PMIs) ranging from 3.7 to 24 h. Multiplex reverse transcriptase PCR (RT-PCR) revealed no VZV transcripts with a PMI of <9 h. Real-time PCR indicated a significant increase (P = 0.02) in VZV ORF63 transcript levels but not the virus DNA burden with longer PMI. Overall, both the breadth of the VZV transcriptome and the VZV ORF63 transcript levels in human cadaver TG increased with longer PMI.

Immunohistochemical detection of intra-neuronal VZV proteins in snap-frozen human ganglia is confounded by antibodies directed against blood group A1-associated antigens

Varicella-zoster virus (VZV) causes chickenpox, establishes latency in trigeminal (TG) and dorsal root ganglia (DRG), and can lead to herpes zoster upon reactivation. The VZV proteome expressed during latency remains ill-defined, and previous studies have shown discordant data on the spectrum and expression pattern of VZV proteins and transcripts in latently infected human ganglia. Recently, Zerboni and colleagues have provided new insight into this discrepancy (Zerboni et al. in J Virol 86:578-583, 2012). They showed that VZV-specific ascites-derived monoclonal antibody (mAb) preparations contain endogenous antibodies directed against blood group A1 proteins, resulting in false-positive intra-neuronal VZV staining in formalin-fixed human DRG. The aim of the present study was to confirm and extend this phenomenon to snap-frozen TG (n=30) and DRG (n=9) specimens of blood group genotyped donors (n=30). The number of immunohistochemically stained neurons was higher with mAb directed to immediate early protein 62 (IE62) compared with IE63. The IE63 mAb-positive neurons always co-stained for IE62 but not vice versa. The mAb staining was confined to distinct large intra-neuronal vacuoles and restricted to A1(POS) donors. Anti-VZV mAb staining in neurons, but not in VZV-infected cell monolayers, was obliterated after mAb adsorption against blood group A1 erythrocytes. The data presented demonstrate that neuronal VZV protein expression detected by ascites-derived mAb in snap-frozen TG and DRG of blood group A1(POS) donors can be misinterpreted due to the presence of endogenous antibodies directed against blood group A1-associated antigens present in ascites-derived VZV-specific mAb preparations.

Recombinant monoclonal antibody recognizes a unique epitope on varicella-zoster virus immediate-early 63 protein

We previously constructed a recombinant monoclonal antibody (rec-MAb 63P4) that detects immediate-early protein IE63 encoded by varicella-zoster virus (VZV) in the cytoplasm of productively infected cells. Here, we used ORF63 truncation mutants to map the rec-MAb 63P4 binding epitope to amino acids 141 to 150 of VZV IE63, a region not shared with other widely used anti-IE63 antibodies, and found that the recombinant antibody does not bind to the simian IE63 counterpart.

Investigation of varicella-zoster virus neurotropism and neurovirulence using SCID mouse-human DRG xenografts

Varicella-zoster virus (VZV) is a medically important human alphaherpesvirus. Investigating pathogenic mechanisms that contribute to VZV neurovirulence are made difficult by a marked host restriction. Our approach to investigating VZV neurotropism and neurovirulence has been to develop a mouse-human xenograft model in which human dorsal root ganglia (DRG) are maintained in severe compromised immunodeficient (SCID) mice. In this review, we will describe our key findings using this model in which we have demonstrated that VZV infection of SCID DRG xenograft results in rapid and efficient spread, enabled by satellite cell infection and polykaryon formation, which facilitates robust viral replication and release of infectious virus. In neurons that persist following this acute replicative phase, VZV genomes are present at low frequency with limited gene transcription and no protein synthesis, a state that resembles VZV latency in the natural human host. VZV glycoprotein I and interaction between glycoprotein I and glycoprotein E are critical for neurovirulence. Our work demonstrates that the DRG model can reveal characteristics about VZV replication and long-term persistence of latent VZV genomes in human neuronal tissues, in vivo, in an experimental system that may contribute to our knowledge of VZV neuropathogenesis.

Varicella zoster virus (VZV) infects and establishes latency in enteric neurons

Case reports have linked varicella-zoster virus (VZV) to gastrointestinal disorders, including severe abdominal pain preceding fatal varicella and acute colonic pseudoobstruction (Ogilvie's syndrome). Because we had previously detected DNA and transcripts encoding latency-associated VZV gene products in the human gut, we sought to determine whether latent VZV is present in the human enteric nervous system (ENS) and, if so, to identify the cells in which it is located and its route to the bowel. Neither DNA, nor transcripts encoding VZV gene products, could be detected in resected gut from any of seven control children (<1 year old) who had not received the varicella vaccine or experienced varicella; however, VZV DNA and transcripts were each found to be present in resected bowel from 6/6 of children with a past history of varicella and in that of 6/7 of children who received the varicella vaccine. Both wild-type (WT) and vaccine-type (vOka) VZV thus establish latent infection in human gut. To determine routes by which VZV might gain access to the bowel, we injected guinea pigs with human or guinea pig lymphocytes expressing green fluorescent protein (GFP) under the control of the VZV ORF66 gene (VZV(OKA66.GFP)). GFP-expressing enteric neurons were found throughout the bowel within 2 days and continued to be present for greater than 6 weeks. DNA encoding VZV gene products also appeared in enteric and dorsal root ganglion (DRG) neurons following intradermal administration of WT-VZV and in enteric neurons after intradermal injection of VZV(OKA66.GFP); moreover, a small number of guinea pig DRG neurons were found to project both to the skin and the intraperitoneal viscera. Viremia, in which lymphocytes carry VZV, or axonal transport from DRG neurons infected through their epidermal projections are thus each potential routes that enable VZV to gain access to the ENS.

Simian varicella virus gene expression during acute and latent infection of rhesus macaques

Varicella zoster virus (VZV) is a neurotropic α-herpesvirus that causes chickenpox during primary infection and establishes latency in sensory ganglia. Reactivation of VZV results in herpes zoster and other neurological complications. Our understanding of the VZV transcriptome during acute and latent infection in immune competent individuals remains incomplete. Infection of rhesus macaques with the homologous simian varicella virus (SVV) recapitulates the hallmarks of VZV infection. We therefore characterized the SVV transcriptome by quantitative real-time reverse transcriptase PCR during acute infection in bronchial alveolar lavage (BAL) cells and peripheral blood mononuclear cells, and during latency in sensory ganglia obtained from the same rhesus macaques. During acute infection, all known SVV open reading frames (ORFs) were detected, and the most abundantly expressed ORFs are involved in virus replication and assembly such as the transcriptional activator ORF 63 and the structural proteins ORF 41 and ORF 49. In contrast, latent SVV gene expression is highly restricted. ORF 61, a viral transactivator and latency-associated transcript, is the most prevalent transcript detected in sensory ganglia. We also detected ORFs A, B, 4, 10, 63, 64, 65, 66, and 68 though significantly less frequently than ORF 61. This comprehensive analysis has revealed genes that potentially play a role in the establishment and/or maintenance of SVV latency.