Varicella-zoster Virus Pathogenesis Research Articles

Varicella zoster virus in human and rat tissue specimens.

The limited supple of appropriate tissues for study has been an impediment to investigations of varicella zoster virus (VZV) latency. Human dorsal root ganglia (DRG) harboring latent virus are not plentiful and are not amenable to manipulation for studying the events surrounding the establishment, maintenance, and cessation of latency. An alternative to studies in human DRG is the rat model of latency, which appears to provide a reliable method of investigating VZV latency. Other alternatives include studies in other human tissues involved in VZV pathogenesis. In order to improve our understanding of the establishment and cessation of latency, we performed comparative immunohistochemical analysis of chickenpox and zoster skin lesions. This analysis revealed that during primary infection and reactivation productive VZV infection occurs in a variety of cell types and that the major VZV DNA binding protein, ORF29p, is present in peripheral axons early during the course of chickenpox. VZV latency was studied in the rat model by in situ hybridization and compared with similar studies performed in human DRG containing latent virus, confirming that VZV DNA persists in the same sites in DRG of the two species.

Sequence Analysis of the Leftward End of Simian Varicella Virus (EcoRI-I Fragment) Reveals the Presence of an 8-bp Repeat Flanking the Unique Long Segment and an 881-bp Open-Reading Frame That Is Absent in the Varicella Zoster Virus Genome

Simian varicella virus (SVV) causes varicella (chickenpox) in nonhuman primates, becomes latent in cranial and dorsal root ganglia, and reactivates to produce zoster (shingles). Because the clinical and molecular features of SVV closely resemble those of varicella zoster virus (VZV) infection of humans, SVV infection of primates has served as an experimental model of VZV pathogenesis and latency. The SVV genome has been completely mapped, but attempts to clone the 3600-bp EcoRI fragment located at the leftward end of the virus genome have hitherto been unsuccessful. Herein, we report the cloning and the complete nucleotide sequence of this region. Comparison of the SVV and VZV sequences in this region revealed an 8-bp inverted repeat sequence flanking the unique long segment of the SVV genome; an 879-bp open-reading frame (ORF) A in SVV that is absent in VZV but has 42% amino acid identity to SVV ORF 4 and 49% to VZV ORF 4; a 342-bp ORF B in SVV with 35% amino acid identity to a 387-bp ORF located to the left of ORF 1 on the VZV genome; and a 303-bp ORF in SVV with 27% amino acid identity to VZV ORF 1. No homologue of VZV ORF 2 was detected. Transcripts specific for ORFs A and B were present in SVV-infected cells in culture and in acutely infected monkey ganglia. Overall, there are more than 2000 bp of DNA in the SVV genome that are absent in the VZV genome.

Experimental simian varicella virus infection of St. Kitts vervet monkeys.

Experimental simian varicella virus (SVV) infection of St. Kitts vervet monkeys was evaluated as an animal model to investigate human varicella-zoster virus (VZV) infections. During the incubation period, viremia disseminated infectious virus throughout the body via infected peripheral blood lymphocytes (PBLs). A vesicular skin rash in the inguinal area, and on the abdomen, extremities, and face appeared on day 7-10 postinfection. Necrosis and hemorrhage in lung and liver tissues from acutely infected monkeys were evident upon histologic analysis. Recovery from simian varicella was accompanied by a rise in the serum neutralizing antibody response to the virus. SVV latency was established in trigeminal ganglia of monkeys which resolved the acute infection. This study indicates that experimental SVV infection of St. Kitts vervets is a useful animal model to investigate SVV and VZV pathogenesis and to evaluate potential antiviral agents and vaccines.

Tropism of varicella-zoster virus for human CD4+ and CD8+ T lymphocytes and epidermal cells in SCID-hu mice

To investigate the cell tropism and pathogenicity of varicella-zoster virus (VZV) strains, we analyzed VZV replication by using SCID-hu mice that carry human fetal thymus/liver implants under the kidney capsule or as subcutaneous fetal skin implants. MRC-5 cells infected with wild-type VZV or the Oka strain, used in the live attenuated varicella vaccine, were injected into the implants. The implants were surgically removed 2, 7, 14, and 21 days postinfection. The VZV titer from infected thymus/liver implants peaked on day 7 for the wild-type strain and on day 14 for the Oka strain. Histological analysis showed necrotic areas characterized by thymocyte depletion and fibrosis. VZV protein synthesis was detectable by immunohistochemical staining in the necrotic areas and in distant regions that did not show cytopathic changes, and VZV DNA was detected by in situ hybridization in the same distribution. Fluorescence-activated cell sorting analysis of thymocytes harvested at day 7 postinfection showed that VZV proteins were expressed in CD4+, CD8+, and CD4+ CD8+ T cells; VZV was cultured from each T-cell subpopulation. The Oka strain had tropism for human cell types similar to that of wild-type VZV. T lymphocytes released infectious VZV, which is a novel and important observation about the replication of this otherwise highly cell associated virus. VZV-infected skin implants exhibited microscopic epidermal lesions that were indistinguishable histologically from the characteristic lesions of varicella. These experiments demonstrate a unique tropism of VZV for human T lymphocytes, explaining its capacity to cause viremia in natural disease, and demonstrate the value of the SCID-hu model for studies of VZV pathogenesis.

Investigation of the Pathogenesis of Varicella-Zoster Virus Infection in Guinea Pigs by Using Polymerase Chain Reaction

The polymerase chain reaction method (PCR) was used to investigate events in the pathogenesis of varicella-zoster virus (VZV) infection in strain 2, Hartley, and euthymic hairless guinea pigs. VZV was detected in peripheral blood mononuclear cells (PBMC) obtained 2-5 days after infection in 8 (50%) of 16 strain 2, 4 (40%) of 10 hairless, and 10 (34%) of 29 Hartley guinea pigs. The frequency of VZV-infected PBMC was estimated to be at least 1/200,000, which is comparable to that observed in human infection. When VZV PCR was used to test ganglia from hairless guinea pigs, samples from 6 of 8 animals were positive. Of 45 VZV-infected guinea pigs that were tested for cellular immunity by VZV T lymphocyte proliferation assay, 44 developed a stimulation index > 2.0. Control animals had no detectable virus by PCR and did not develop cellular immunity to VZV. These experiments showed that viremia was detectable by PCR during primary VZV infection of guinea pigs in about half of the animals regardless of the strain of guinea pig. Acquisition of cellular immunity provided a consistent marker of infection in all guinea pig strains. PCR was also useful for demonstrating VZV in guinea pig ganglia tissue, with VZV gene sequences being detectable for at least 80 days after infection. With the combination of PCR and immunologic assays, various guinea pig strains should be useful for studies of VZV pathogenesis and for the evaluation of antiviral agents and vaccine strategies.

Varicella in Hairless Guinea Pigs

A high proportion of depilated newborn or euthymic congenitally hairless adult guinea pigs develop an erythematous papular exanthem during infection with varicella-zoster virus (VZV) previously cultivated in guinea pig cell culture. Virus has been demonstrated in tissues during varicella using polymerase chain reaction amplification and nucleic acid hybridization methods. The frequency of exanthem expression can be reduced by the prophylactic administration of VZV convalescent-phase guinea pig serum. This model should prove useful for further study of VZV pathogenesis as well as for testing putative antiviral compounds.