Varicella-zoster virus. The virus

Neurological manifestations of patients with COVID-19: potential routes of SARS-CoV-2 neuroinvasion from the periphery to the brain

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2), has caused a global pandemic in only 3 months. In addition to major respiratory distress, characteristic neurological manifestations are also described, indicating that SARS-CoV-2 may be an underestimated opportunistic pathogen of the brain. Based on previous studies of neuroinvasive human respiratory coronaviruses, it is proposed that after physical contact with the nasal mucosa, laryngopharynx, trachea, lower respiratory tract, alveoli epithelium, or gastrointestinal mucosa, SARS-CoV-2 can induce intrinsic and innate immune responses in the host involving increased cytokine release, tissue damage, and high neurosusceptibility to COVID-19, especially in the hypoxic conditions caused by lung injury. In some immune-compromised individuals, the virus may invade the brain through multiple routes, such as the vasculature and peripheral nerves. Therefore, in addition to drug treatments, such as pharmaceuticals and traditional Chinese medicine, non-pharmaceutical precautions, including facemasks and hand hygiene, are critically important.

Probing of the nuclear import and export signals and subcellular transport mechanism of varicella-zoster virus tegument protein open reading frame 10

Varicella-zoster virus open reading frame 10 (ORF10), a tegument protein present in the virion, is a member of the alphaherpesvirus UL48 gene family that shares considerable amino acid sequence homology with the UL48 prototype, herpes simplex virus type 1 VP16. VP16 serves multiple functions, including transcriptional activation of viral immediate-early genes. Furthermore, VP16 has been shown to be involved in some aspects of virus assembly and/or maturation. However, little is known concerning the function of ORF10. Here, we found that transient expression of ORF10 fused to enhanced yellow fluorescent protein (EYFP) in COS-7 cells showed the predominantly nuclear localization in the absence of other viral proteins. By constructing a series of ORF10 variants fused to EYFP, a bona fide bipartite nuclear localization signal of ORF10 was, for the first time, determined and mapped to amino acids (aa) 302-347. Additionally, the nuclear export signal (NES) was identified and found to be in a leucine-rich region at aa 226-236. Finally, ORF10 was demonstrated to be targeted to the cytoplasm through the functional NES by chromosomal region maintenance 1-dependent pathway, and to the nucleus via Ran and importin β1-dependent pathway that does not require importin α5.

Characterization of the nuclear import and export signals, and subcellular transport mechanism of varicella-zoster virus ORF9

Varicella-zoster virus (VZV) open reading frame 9 (ORF9) mRNA is one of the most abundantly expressed messages during VZV infection. However, little is known concerning the function of ORF9 protein. Here, we found that transient expression of ORF9 fused to enhanced yellow fluorescent protein (EYFP) in COS-7 cells showed a predominantly cytoplasmic localization in the absence of other viral proteins. By constructing a series of ORF9 variants fused to EYFP, a bona fide bipartite nuclear localization signal of ORF9 was, for the first time, determined and mapped to aa 16-32 (RRKTTPSYSGQYRTARR). Additionally, the nuclear export signal (NES) was identified and found to be in a leucine-rich region at aa 103-117 (LRHELVEDAVYENPL). Finally, ORF9 was demonstrated to be targeted to the cytoplasm through the functional NES by Ran and the chromosomal region maintenance 1-dependent pathway, and to the nucleus via an importin β-dependent pathway that does not require importin α5.

Prevention strategies for herpes zoster and post-herpetic neuralgia

Impairment of varicella zoster virus (VZV)-specific cell-mediated immunity, including impairment due to immunosenescence, is associated with an increased risk of developing herpes zoster (HZ), whereas levels of anti-VZV antibodies do not correlate with HZ risk. This crucial role of VZV-specific cell-mediated immunity suggests that boosting these responses by vaccination will be an effective strategy for reducing the burden of HZ. Other strategies focus on preventing the major complication of HZ--post-herpetic neuralgia. These strategies include pre-emptive treatment with drugs such as tricyclic antidepressants, anticonvulsants and analgesics.

A self-excisable infectious bacterial artificial chromosome clone of varicella-zoster virus allows analysis of the essential tegument protein encoded by ORF9

In order to facilitate the generation of mutant viruses of varicella-zoster virus (VZV), the agent causing varicella (chicken pox) and herpes zoster (shingles), we generated a full-length infectious bacterial artificial chromosome (BAC) clone of the P-Oka strain. First, mini-F sequences were inserted into a preexisting VZV cosmid, and the SuperCos replicon was removed. Subsequently, mini-F-containing recombinant virus was generated from overlapping cosmid clones, and full-length VZV DNA recovered from the recombinant virus was established in Escherichia coli as an infectious BAC. An inverted duplication of VZV genomic sequences within the mini-F replicon resulted in markerless excision of vector sequences upon virus reconstitution in eukaryotic cells. Using the novel tool, the role in VZV replication of the major tegument protein encoded by ORF9 was investigated. A markerless point mutation introduced in the start codon by two-step en passant Red mutagenesis abrogated ORF9 expression and resulted in a dramatic growth defect that was not observed in a revertant virus. The essential nature of ORF9 for VZV replication was ultimately confirmed by restoration of the growth of the ORF9-deficient mutant virus using trans-complementation via baculovirus-mediated gene transfer.

Viral interference with MHC class I antigen presentation pathway: the battle continues

CD8+ cytotoxic T lymphocytes (CTLs) play a critical role in the defense against viral infections. In general, CD8+ CTLs recognize antigenic peptides in the context of the major histocompatibility complex (MHC) class I molecule. The MHC class I molecules are expressed on almost all the nucleated cells in the body. The trimolecular complex consisting of the class I heavy chain, beta2-microglobulin and the peptide are generated by the MHC class I antigen presentation pathway. This pathway is designed to sample the intracellular milieu and present the information to the CTLs trafficking the area. This rigorous sampling of intracellular environment enables the CTLs to quickly identify and eliminate the cells that synthesize non-self proteins as a result of a viral infection. Many viruses, including several viruses of veterinary importance, have evolved astounding strategies to interfere with the MHC class I antigen presentation pathway, as a means of evading the CTL response of the host. This review focuses on the diverse mechanisms of viral evasion of the MHC class I antigen presentation pathway with particular emphasis on viruses of veterinary importance.

Does antigenic overload exist? The role of multiple immunizations in infants

There is no evidence that currently recommended vaccines overload or weaken the infant immune system. Infants have an enormous capacity to respond safely and effectively to multiple vaccines. The schedule for the administration of childhood vaccines is tailored to the unique developmental pattern of the infant immune system. Childhood vaccines provide immediate protection from common childhood illness and establish the foundation for lifelong immunity that develops with subsequent vaccination or infection. Widespread vaccination of infants and children represents a public health triumph of the 20th century. This fact must be reinforced continually by health care workers and parent education to help maintain progress in the 21st century.

Immunology of Varicella Immunization in the elderly

OBJECTIVE

To review the varicella-zoster virus (VZV) and herpes zoster disease and to summarize published reports on the use of the live-attenuated varicella zoster vaccine to enhance cell-mediated immunity in elderly individuals.

DATA SOURCE

A MEDLINE search (1966-August 1999) for English-language clinical studies and review articles pertaining to VZV and the live-attenuated varicella vaccine was conducted; references obtained from these publications were subsequently reviewed for additional relevant articles.

STUDY SELECTION AND DATA EXTRACTION

Representative clinical trials were summarized and relevant information was selected to assist in the understanding of VZV, the subsequent immune response, and the live-attenuated varicella vaccine.

DATA SYNTHESIS

The physiologic, age-related decline in VZV cell-mediated immunity has been shown to be restored on administration of live-attenuated varicella vaccine. Various studies report serum anti-VZV antibody concentrations, and production of interferon-gamma were increased following vaccination. Concentrations subsequently returned to baseline one year after vaccination. Increase in responder cell frequency, a measure of cell-mediated immunity, has been reported to last up to four years after vaccination, at concentrations similar or superior to those observed following herpes zoster.

CONCLUSIONS

Enhancement of cell-mediated immune response in elderly individuals through vaccination with live-attenuated varicella vaccine is a possible measure to protect this population from herpes zoster and to attenuate its complications. A summary of immunogenicity studies to identify the immune response to live-attenuated varicella vaccine in the elderly is presented. The absolute clinical significance, as well as appropriate administration guidelines of this prophylactic intervention, will become evident following forthcoming large, masked, placebo-controlled trials.

Varicella zoster viral disease

Herpes zoster is cause of considerable morbidity, especially among elderly patients, with a suggestion of a slight increase in incidence among female patients. Substantial research on the biology of the varicella zoster virus has led to advances in our knowledge of the pathophysiology of the disease along with more successful therapy for the acute episodes of herpes zoster. Ophthalmic zoster is more common than zoster in other cranial nerves and is associated with pronounced suffering. This article reviews the epidemiology, biology, and latency of herpes zoster, discusses the pathophysiology of the disease, and describes treatment options with antivirals and corticosteroids. The pathophysiology and treatment options for postherpetic neuralgia are also addressed. The varicella vaccine is now available, and initial results suggest that this may lessen the effect of herpes zoster in the future.