Varicella-zoster virus (VZV) is a ubiquitous human alphaherpesvirus that causes varicella (chicken pox) and herpes zoster (shingles). Varicella is a common childhood illness, characterized by fever, viremia, and scattered vesicular lesions of the skin. As is characteristic of the alphaherpesviruses, VZV establishes latency in cells of the dorsal root ganglia. Herpes zoster, caused by VZV reactivation, is a localized, painful, vesicular rash involving one or adjacent dermatomes. The incidence of herpes zoster increases with age or immunosuppression. The VZV virion consists of a nucleocapsid surrounding a core that contains the linear, double-stranded DNA genome; a protein tegument separates the capsid from the lipid envelope, which incorporates the major viral glycoproteins. VZV is found in a worldwide geographic distribution but is more prevalent in temperate climates. Primary VZV infection elicits immunoglobulin G (IgG), IgM, and IgA antibodies, which bind to many classes of viral proteins. Virus-specific cellular immunity is critical for controlling viral replication in healthy and immunocompromised patients with primary or recurrent VZV infections. Rapid laboratory confirmation of the diagnosis of varicella or herpes zoster, which can be accomplished by detecting viral proteins or DNA, is important to determine the need for antiviral therapy. Acyclovir is licensed for treatment of varicella and herpes zoster, and acyclovir, valacyclovir, and famciclovir are approved for herpes zoster. Passive antibody prophylaxis with varicella-zoster immune globulin is indicated for susceptible high-risk patients exposed to varicella. A live attenuated varicella vaccine (Oka/Merck strain) is now recommended for routine childhood immunization.

Varicella-zoster virus.

Patients at High Risk of Morbidity or Mortality from Varicella–Zoster Virus Recognition of the potential severity of varicella in immunocompromised patients dates from our post-mortem studies of tw...

Varicella and herpes zoster. Changing concepts of the natural history, control, and importance of a not-so-benign virus.

Poliovirus vaccine-live

One hundred ninety-one varicella-susceptible children with leukemia in remission were immunized with live attenuated varicella vaccine. There was serological evidence of an immune response in approximately 80% after one dose and in more than 90% after two doses. The major side effect was mild to moderate rash, seen especially in children with maintenance chemotherapy suspended for one week before and one week after vaccination. Children with rash had higher antibody titers than those without rash, but those with rash were also at risk (10%) to transmit vaccine virus to others. Twenty-two vaccinees subsequently had household exposures to varicella or zoster. The attack rate of clinical varicella in these vaccinees was 18%, significantly lower than the attack rate of approximately 90% in varicella-susceptible persons with household exposures. All cases of clinical illness were extremely mild, with an average of about 50 vesicles. The mild character of the illness was clearly different than varicella in unimmunized children receiving chemotherapy for leukemia. Varicella vaccine was approximately 80% effective in preventing clinical varicella in children with leukemia and completely effective in preventing severe varicella in this high-risk group. (JAMA1984;252:355-362)

Live Attenuated Varicella Vaccine: Efficacy for Children With Leukemia in Remission

The SCID-hu mouse implanted with human fetal tissue is a novel model for investigating human viral pathogenesis. Infection of human skin implants was used to investigate the basis for the clinical attenuation of the varicella-zoster virus (VZV) strain, V-Oka, from which the newly licensed vaccine is made. The pathogenicity of V-Oka was compared with that of its parent, P-Oka, another low-passage clinical isolate, strain Schenke (VZV-S), and VZV-Ellen, a standard laboratory strain. The role of glycoprotein C (gC) in infectivity for human skin was assessed by using gC-negative mutants of V-Oka and VZV-Ellen. Whereas all of these VZV strains replicated well in tissue culture, only low-passage clinical isolates were fully virulent in skin, as shown by infectious virus yields and analysis of implant tissues for VZV DNA and viral protein synthesis. The infectivity of V-Oka in skin was impaired compared to that of P-Oka, providing the first evidence of a virologic basis for the clinical attenuation of V-Oka. The infectivity of V-Oka was further diminished in the absence of gC expression. All strains except gC-Ellen retained some capacity to replicate in human skin, but cell-free virus was recovered only from implants infected with P-Oka or VZV-S. Although VZV is closely related to herpes simplex virus type 1 (HSV-1) genetically, experiments in the SCID-hu model revealed differences in tropism for human cells that correlated with differences in VZV and HSV-1 disease. VZV caused extensive infection of epidermal and dermal skin cells, while HSV-1 produced small, superficial lesions restricted to the epidermis. As in VZV, gC expression was a determinant for viral replication in skin. VZV infects human CD4+ and CD8+ T cells in thymus/liver implants, but HSV-1 was detected only in epithelial cells, with no evidence of lymphotropism. These SCID-hu mouse experiments show that the clinical attenuation of the varicella vaccine can be attributed to decreased replication of V-Oka in skin and that tissue culture passage alone reduces the ability of VZV to infect human skin in vivo. Furthermore, gC, which is dispensable for replication in tissue culture, plays a critical role in the virulence of the human alphaherpesviruses VZV and HSV-1 for human skin.

Attenuation of the Vaccine Oka Strain of Varicella-Zoster Virus and Role of Glycoprotein C in Alphaherpesvirus Virulence Demonstrated in the SCID-hu Mouse

The development of serum and nasopharyngeal antibody responses to varicella-zoster virus (VZV) was studied in groups of children after naturally acquired varicella or after immunization with the Oka strain of live attenuated VZV vaccine administered in varying doses via respiratory inhalation or subcutaneous injection. Natural infection, subcutaneous immunization, and respiratory inhalation of large doses of VZV vaccine consistently resulted in the development of VZV-specific IgG antibody responses in serum. Although the serum IgG antibody responses persisted for at least eight to 12 months (to date) after either form of infection, the antibody activity appeared to be four- to eight-fold higher after natural infection than after immunization. Transient IgG antibody responses were observed in serum after respiratory inhalation of smaller doses of VZV vaccine. Natural infection, but not VZV vaccine, was associated with the development of serum and nasopharyngeal IgA responses to VZV in most subjects.

H. Yabuuchi

Papers

Antibody Response to Varicella-Zoster Virus after Natural or Vaccine-Induced Infection