Evaluation of the time resolved fluorescence immunoassay (TRFIA) for the detection of varicella zoster virus (VZV) antibodies following vaccination of healthcare workers

Determination of varicella zoster virus (VZV) immunity in healthcare workers without a history of chickenpox is important for identifying those in need of vOka vaccination. Post immunisation, healthcare workers in the UK who work with high risk patients are tested for seroconversion. To assess the performance of the time-resolved fluorescence immunoassay (TRFIA) for the detection of antibody in vaccinated as well as unvaccinated individuals, a cut-off was first calculated. VZV-IgG specific avidity and titres six weeks after the first dose of vaccine were used to identify subjects with pre-existing immunity among a cohort of 110 healthcare workers. Those with high avidity (≥ 60%) were considered to have previous immunity to VZV and those with low or equivocal avidity (<60%) were considered naive. The former had antibody levels ≥ 400 mIU/mL and latter had levels < 400 mIU/mL. Comparison of the baseline values of the naive and immune groups allowed the estimation of a TRFIA cut-off value of > 130 mIU/mL which best discriminated between the two groups and this was confirmed by ROC analysis. Using this value, the sensitivity and specificity of TRFIA cut-off were 90% (95% CI 79-96), and 78% (95% CI 61-90) respectively in this population. A subset of samples tested by the gold standard Fluorescence Antibody to Membrane Antigen (FAMA) test showed 84% (54/64) agreement with TRFIA.

Persistence of varicella-zoster virus viraemia in patients with herpes zoster

BACKGROUND

Herpes zoster is caused by the reactivation of varicella-zoster virus from sensory neurons. The commonest complication following zoster is chronic pain termed post herpetic neuralgia.

OBJECTIVES

To investigate the dynamics of VZV viraemia and viral load following the resolution of zoster and its relationship to PHN development.

STUDY DESIGN

Blood samples were collected at baseline, 1 month, 3 months and 6 month from a prospective study of 63 patients with active zoster. Quantification of VZV DNA in whole blood was performed using a real-time PCR assay.

RESULTS

During acute zoster, all patients had detectable VZV DNA in their blood. VZV DNA remained detectable in the blood of 91% of patients at 6 months although levels declined significantly (p<0.0001). A history of prodromal symptoms (p=0.005) and severity of pain at baseline (p=0.038) as well as taking antivirals (p=0.046) and being immunocompromised (p=0.043) were associated, with longer time to recovery from PHN. Viral DNA loads were consistently higher in patients with risk factors for PHN and higher viral DNA loads over time were associated with longer time to recovery (p=0.058 overall and 0.038 in immunocompetent).

CONCLUSIONS

Based on these observations we hypothesise that VZV replication persists following acute shingles and that higher viral DNA loads contribute to the risk factors for PHN.

Effect of viral load on the outcome of herpes zoster

Varicella-zoster virus (VZV) is a member of the Herpesviridae family, primary infection with which causes varicella, more commonly known as chicken pox. Characteristic of members of the alphaherpesvirus subfamily, VZV is neurotropic and establishes latency in sensory neurons. Reactivation of VZV causes herpes zoster, also known as shingles. The most frequent complication following zoster is chronic and often debilitating pain called postherpetic neuralgia (PHN), which can last for months after the disappearance of a rash. During episodes of acute zoster, VZV viremia occurs in some, but not all, patients; however, the effect of the viral load on the disease outcome is not known. Here we describe the development of a highly specific, sensitive, and reproducible real-time PCR assay to investigate the factors that may contribute to the presence and levels of baseline viremia in patients with zoster and to determine the relationship between viremia and the development and persistence of PHN. VZV DNA was detected in the peripheral blood mononuclear cells (PBMCs) of 78% of patients with acute zoster and in 9% of healthy asymptomatic blood donors. The presence of VZV in the PBMCs of patients with acute zoster was independently associated with age and being on antivirals but not with gender, immune status, extent of rash, the age of the rash at the time of blood sampling, having a history of prodromal pain, or the extent of acute pain. Prodromal pain was significantly associated with higher baseline viral loads. Viral load levels were not associated with the development or persistence of PHN at 6, 12, or 26 weeks.

Varicella-zoster-virus genotypes in East London: a prospective study in patients with herpes zoster

A total of 298 patients with herpes zoster were recruited as part of 2 community-based studies in East London between 1998 and 2003. Single nucleotide-polymorphism analysis of 4 regions (genes 1, 21, 37, and 60) found that most genotypes were European strains C and B, representing 58% and 21% of all samples collected. No change in the proportion of these European clades has occurred during the past 80 years, strongly supporting the hypothesis that these strains are indigenous to the United Kingdom. White patients almost exclusively had reactivation of genotypes C (66%) and B (21%), whereas patients from Africa, Asia, or the Caribbean mainly had reactivation of genotypes A and J. An increase in BglI-positive A and J genotypes in UK cases of zoster is only partly explained by immigration from endemic regions. The data presented provide a baseline against which to evaluate changes in the molecular epidemiology of varicella-zoster virus and the effect of immunization with the Japanese Oka vaccine strain.

Reactivation of 2 genetically distinct varicella-zoster viruses in the same individual

Varicella-zoster viruses recovered from 2 episodes of herpes zoster in an immunocompetent man were found to be different genotypes. The fact that the 2 isolates came from the same individual was confirmed by DNA fingerprinting. Immunity following chickenpox may not always protect against systemic reinfection. This finding raises questions about varicella-zoster virus pathogenesis and may have an impact on public health policy.

Genetic variation of varicella-zoster virus: evidence for geographical separation of strains

Heteroduplex mobility assay was used to identify variants of varicella-zoster virus (VZV) circulating in the United Kingdom and elsewhere. Forty variable positions were identified. Sixteen substitutions were non-synonymous, resulting in an amino acid change, the majority of which were clustered within surface expressed proteins. Phylogenetic analysis distinguished at least three major clades (strains A, B, C) supported by significant bootstrap values. Apart from the United Kingdom and Brazil where all three strains were found, genotypes appeared to be closely associated with the geographical region in which they were sampled. Allelic co-segregation of widely spaced single nucleotide polymorphisms (SNPs) confirmed the genetic stability of the VZV. Recombination rates were difficult to calculate because of the low intra genotypic variation. However, one haplotype originating from Brazil is most parsimoniously explained as a recombinant between A and C strains, which co-occur in the region. Two further UK strains appeared to be recombinants between groups B and C.