Mark Quinlivan

Safety profile of live varicella virus vaccine (Oka/Merck): five-year results of the European Varicella Zoster Virus Identification Program (EU VZVIP).

BACKGROUND VARIVAX (Oka/Merck) is a live varicella vaccine, licensed in Europe since 2003. In addition to routine safety surveillance, the Varicella Zoster Virus Identification Program (VZVIP) analyzes clinical samples to establish whether adverse events (AEs) are associated with wild-type (wt) or vaccine varicella zoster virus (vVZV) strain. The European VZVIP provides data on VZV clade distribution. METHODS Samples were collected from patients with selected AEs; the VZV strain was determined using polymerase chain reaction. RESULTS From October 2003 to September 2008, 1006 spontaneous AE reports were analyzed (88% non-serious). Samples from 76/585 cases with selected AEs were collected. Of 55 VZV-positive/typable samples, wtVZV was detected in 40 and vVZV in 15 samples. Most rashes (32/44) <or=42 days postvaccination were associated with wtVZV. For breakthrough varicella, 6/9 cases were wtVZV-positive; none were vVZV-positive. For herpes zoster 9/17 cases were VZV-positive: eight vVZV, one wtVZV. One case of mild encephalitis was associated with vVZV. One of three cases of suspected secondary vVZV transmission was confirmed. Most wtVZV was clade 3 and clade 1. CONCLUSIONS European experience confirms that Oka/Merck vaccine is generally well tolerated. wtVZV genotypes were consistent with the molecular epidemiology of VZV in Europe.

Genotyping of Varicella-Zoster Virus and the Discrimination of Oka Vaccine Strains by TaqMan Real-Time PCR

ABSTRACT Single nucleotide polymorphisms (SNPs) in five genes have been used to identify four major subtypes of wild-type varicella-zoster virus (VZV) A, B, C, and J. Additional SNPs, located in the IE62 major transactivating gene can be used to differentiate the Oka vaccine strain (vOka) from wild-type VZV. Primer-probe sets for the detection of the five polymorphic loci were designed by Applied Biosystems for the ABI 7900HT platform. Probes for each allele were labeled with VIC or 6-carboxyfluorescein fluorogenic markers. Each primer-probe set was validated to establish assay sensitivity and specificity using VZV DNA of predetermined copy number and genotype. Further evaluation was carried out using DNA samples from the vesicle fluid or skin swab of the rash of adult patients with herpes zoster or rashes due to vOka. Assay sensitivity ranged from 10 and 108 copies/ml of VZV DNA (equivalent to 2 to 20 copies per reaction). Statistical analyses showed that for each genotype, a set of two probes clearly differentiated the nucleotide present (allele) at that locus (P < 0.0001). It was possible to determine the genotype of wild-type VZV using one of four SNP assays and also to differentiate wild type from vOka using a single SNP assay. The assay can be used for diagnostic and epidemiological studies of VZV, including the differentiation of vOka from wild-type strains, investigation of breakthrough infections, and varicella outbreaks following immunization.

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.

Subclinical VZV reactivation in immunocompetent children hospitalized in the ICU associated with prolonged fever duration

A prospective observational study was conducted to examine whether asymptomatic VZV reactivation occurs in immunocompetent children hospitalized in an ICU and its impact on clinical outcome. A secondary aim was to test the hypothesis that vaccinated children have a lower risk of reactivation than naturally infected children. Forty immunocompetent paediatric ICU patients and healthy controls were enrolled. Patients were prospectively followed for 28 days. Clinical data were collected and varicella exposure was recorded. Admission serum levels of TNF-a, cortisol and VZV-IgG were measured. Blood and saliva samples were collected for VZV-DNA detection via real-time PCR. As a comparison, the detection of HSV-DNA was also examined. Healthy children matched for age and varicella exposure type (infection or vaccination) were also included. VZV reactivation was observed in 17% (7/39) of children. Children with VZV reactivation had extended duration of fever (OR = 1.17; 95% CI, 1.02-1.34). None of the varicella-vaccinated children or healthy controls had detectable VZV-DNA in any blood or saliva samples examined. HSV-DNA was detected in saliva from 33% of ICU children and 2.6% of healthy controls. Among children with viral reactivation, typing revealed wild-type VZV and HSV-1. In conclusion, VZV reactivation occurs in immunocompetent children under severe stress and is associated with prolonged duration of fever.

A case of varicella caused by co-infection with two different genotypes of varicella–zoster virus

We describe for the first time a case of varicella caused by co-infection with 2 genotypes of Varicella-zoster virus in a 19 month old child 3 days post-immunization with the varicella live vaccine. The presence of 2 different wild-type viruses in vesicular fluid was confirmed by amplification from single virus genomes and genotyping of single nucleotide polymorphisms (SNPs) known to distinguish the 5 different genotypes of VZV. The finding has important implications for recombination of wild type VZV.

Vaccine oka varicella-zoster virus genotypes are monomorphic in single vesicles and polymorphic in respiratory tract secretions

We previously found that, after immunization with vaccine Oka varicella-zoster virus, virus obtained from a single vesicle were monomorphic, and virus obtained from different individuals were heterogeneous. Here we show that virus obtained from the lungs of a patient were a mixture of vaccine Oka variants. We hypothesize that complications after immunization are unlikely to be caused by expansion of a single, biologically more virulent clone of virus that either pre-exists in the vaccine or develops after random mutation of different clones. We hypothesize that some clones are more trophic than others for skin.

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. Copyright

Use of Oral Fluid to Examine the Molecular Epidemiology of Varicella Zoster Virus in the United Kingdom and Continental Europe

We investigated oral fluid (OF) as an alternative to sampling of rashes for varicella zoster virus (VZV) genotyping and further characterized VZV clade prevalence in the United Kingdom and Europe. VZV was detected in up to 91% of OF specimens. Paired OF and vesicle fluid samples contained identical VZV clades. While clades 1 and 3 were the most prevalent across the United Kingdom and Europe, in Western Europe, clade 5 viruses were circulating. Viruses from the same outbreak belonged to different clades, but no clade was associated with a severe-disease phenotype. OF is suitable and convenient for large-scale molecular epidemiological studies of VZV.

Molecular and therapeutic aspects of varicella-zoster virus infection.

Varicella-zoster virus (VZV) is a highly species-specific member of the Herpesviridae family. The virus exhibits multiple cell tropisms, infecting peripheral blood mononuclear cells and skin cells before establishing latency in sensory neurons. Such tropisms are essential both for primary infection, which manifests itself as chickenpox (varicella), and subsequent reactivation to cause herpes zoster (shingles). The highly cell-associated nature of the virus, coupled with its narrow host range, has resulted in the lack of an animal model that mimics its diseases in humans, thereby greatly hindering the study of events in VZV pathogenesis. Despite this, extensive studies both in vitro and in vivo in small-animal models have provided a fascinating insight into molecular events that govern VZV diseases. In addition, VZV has become the first human herpes virus for which a live attenuated vaccine has been developed.

Cytomegalovirus seropositivity is associated with herpes zoster.

Herpes zoster (HZ) is caused by VZV reactivation that is facilitated by a declined immunity against varicella-zoster virus (VZV), but also occurs in immunocompetent individuals. Cytomegalovirus (CMV) infection is associated with immunosenescence meaning that VZV-specific T-cells could be less responsive. This study aimed to determine whether CMV infection could be a risk factor for the development of HZ. CMV IgG serostatus was determined in stored serum samples from previously prospectively recruited ambulatory adult HZ patients in the UK (N = 223) in order to compare the results with those from UK population samples (N = 1545) by means of a logistic regression (controlling for age and gender). Furthermore, we compared the UK population CMV seroprevalence with those from population samples from other countries (from Belgium (N1 = 1741, N2 = 576), USA (N = 5572) and Australia (N = 2080)). Furthermore, CMV IgG titers could be compared between UK HZ patients and Belgium N2 population samples because the same experimental set-up for analysis was used. We found UK ambulatory HZ patients to have a higher CMV seroprevalence than UK population samples (OR 1.56 [1.11 2.19]). CMV IgG seropositivity was a significant risk factor for HZ in the UK (OR 3.06 [1.32 7.04]. Furthermore, high CMV IgG titers (exceeding the upper threshold) were less abundant in CMV-seropositive Belgian N2 population samples than in CMV-seropositive UK HZ patients (OR 0.51 [0.31 0.82]. We found CMV-seroprevalence to increase faster with age in the UK than in other countries (P < 0.05). We conclude that CMV IgG seropositivity is associated with HZ. This finding could add to the growing list of risk factors for HZ.