Comparative analysis of the restriction endonuclease profiles of the Dumas and Singapore strains of varicella-zoster virus

Changing seroprevalence of varicella zoster virus infection in a tropical city state, Singapore

OBJECTIVE

To understand the seroepidemiology of varicella zoster virus (VZV) in the Singaporean population, based on a paediatric survey conducted in 2008-2010 and the 2010 National Health Survey. The findings were compared with previous studies carried out in 1989-1990, 1993, 1998, and 2004.

METHODS

The paediatric survey involved 1200 subjects; residual diagnostic serum samples were collected from Singapore residents aged 1-17 years at two hospitals. The adult survey involved 3293 subjects; residual serum samples were obtained from Singapore residents aged 18-79 years who had participated in the 2010 National Health Survey.

RESULTS

The seroprevalence in children under 5 years of age increased from 4% in 1989/1990 to 11.7% in 1998 and 33.2% in 2008-2010. For children aged 5-14 years, the corresponding seroprevalences were 22.8%, 59.5%, and 58.0%. The seroprevalence in children aged 5-14 years in 2008-2010 was not significantly different from that in 1998 (p=0.721). Among Singapore adults over 25 years of age, the seroprevalence remained consistently high at around 88% from 1998/1990 to 2010.

CONCLUSIONS

Nearly two-thirds of pre-school children, 39.5% of primary school children, and 29% of adolescents aged 13-17 years are susceptible to VZV infection. At this level of immunity, it can be expected that outbreaks will continue to occur unless the varicella vaccine is introduced into the national childhood immunization programme.

Bioinformatics of varicella-zoster virus: single nucleotide polymorphisms define clades and attenuated vaccine genotypes

Varicella zoster virus (VZV) is one of the human herpesviruses. To date, over 40 complete VZV genomes have been sequenced and analyzed. The VZV genome contains around 125,000 base pairs including 70 open reading frames (ORFs). Enumeration of single nucleotide polymorphisms (SNPs) has determined that the following ORFs are the most variable (in descending order): 62, 22, 29, 28, 37, 21, 54, 31, 1 and 55. ORF 62 is the major immediate early regulatory VZV gene. Further SNP analysis across the entire genome has led to the observation that VZV strains can be broadly grouped into clades within a phylogenetic tree. VZV strains collected in Singapore provided important sequence data for construction of the phylogenetic tree. Currently five VZV clades are recognized; they have been designated clades 1 through 5. Clades 1 and 3 include European/North American strains; clade 2 includes Asian strains, especially from Japan; and clade 5 includes strains from India. Clade 4 includes some strains from Europe, but its geographic origins need further documentation. Within clade 1, five variant viruses have been isolated with a missense mutation in the gE (ORF 68) glycoprotein; these strains have an altered increased cell spread phenotype. Bioinformatics analyses of the attenuated vaccine strains have also been performed, with a subsequent discovery of a stop-codon SNP in ORFO as a likely attenuation determinant. Taken together, these VZV bioinformatics analyses have provided enormous insights into VZV phylogenetics as well as VZV SNPs associated with attenuation.

VZV molecular epidemiology

The molecular epidemiology of varicella zoster virus (VZV) has led to an understanding of virus evolution, spread, and pathogenesis. The availability of over 20 full length genomes has confirmed the existence of at least five virus clades and generated estimates of VZV evolution, with evidence of recombination both past and ongoing. Genotyping by restriction enzyme analysis (REA) and single nucleotide polymorphisms (SNP) has proven that the virus causing varicella is identical to that which later reactivates as zoster in an individual. Moreover, these methods have shown that reinfection, which is mostly asymptomatic, may also occur and the second virus may establish latency and reactivate. VZV is the only human herpesvirus that is spread by the respiratory route. Genotyping methods, together with epidemiological data and modeling, have provided insights into global differences in the transmission patterns of this ubiquitous virus.

Divergence and genotyping of human alpha-herpesviruses: an overview

Herpesviruses are large DNA viruses that are highly disseminated among animals. Of the eight herpesviruses identified in humans, three are classified into the alpha-herpesvirus subfamily: herpes simplex virus types 1 (HSV-1) and 2 (HSV-2), which are typically associated with mucocutaneous lesions, and varicella-zoster virus (VZV), which is the cause of chicken pox and herpes zoster. All three viruses establish lifelong infections and may also induce more severe symptoms, such as neurological manifestations and fatal neonatal infections. Despite thorough investigation of the genetic variability among circulating strains of each virus in recent decades, little is known about possible associations between the genetic setups of the viruses and clinical manifestations in human hosts. This review focuses mainly on evolutionary studies of and genotyping strategies for these three human alpha-herpesviruses, emphasizing the ambiguities induced by a high frequency of circulating recombinant strains. It also aims to shed light on the challenges of establishing a uniform genotyping strategy for all three viruses.

Identification of five major and two minor genotypes of varicella-zoster virus strains: a practical two-amplicon approach used to genotype clinical isolates in Australia and New Zealand

Whole genome phylogenetic analysis in this study resolved a total of five major genotypes among the 22 varicella-zoster virus (VZV) strains or isolates for which complete genomic sequences are available. Consistent with earlier publications we have designated these genotypes European 1 (E1), European 2 (E2), Japanese (J), mosaic 1 (M1), and mosaic 2 (M2). Single nucleotide polymorphism (SNP) analysis performed in a whole-genome alignment revealed that VZV isolates of all five genotypes can be accurately genotyped using SNPs from two amplicons: open reading frame 22 (ORF22) and either ORF21 or ORF50. This modified approach identifies all of the genotypes observed using any of the published genotyping protocols. Of 165 clinical varicella and zoster isolates from Australia and New Zealand typed using this approach, 67 of 127 eastern Australian isolates were E1, 30 were E2, 16 were J, 10 were M1, and 4 were M2; 25 of 38 New Zealand isolates were E1, 8 were E2, and 5 were M1. VZV strain diversity in eastern Australia is thus broader than has been described for any other region, including Europe, Africa, and North America. J strains were far more prevalent than previously observed in countries other than Japan. Two-amplicon typing was in complete accord with genotypes derived using SNP in multiple ORFs (ORFs 1, 21, 22, 38, 50, 54, and 62). Two additional minor genotypes, M3 and M4, could also be resolved using two-amplicon typing.

Genotypic analysis of varicella-zoster virus and its seroprevalence in Finland

We evaluated the seroprevalence of varicella-zoster virus (VZV) in the Finnish population among various age groups and genetically characterized VZV strains from documented cases of varicella and zoster. VZV-specific immunoglobulin G was measured in 2,842 serum samples that had been submitted for virological studies to the Department of Virology, University of Helsinki, from 1995 to 1996. Specimens for VZV genotyping were obtained from vesicular lesions from two pediatric patients and 26 adult patients. Seroprevalence to VZV varied markedly by age: 45% in children aged < or = 2 months, 12.5% in children aged 6 to 8 months, and > 90% in children near 10 years of age, plateauing thereafter into advanced age. The seroprevalence rates indicate that in Finland, as in other countries with temperate climates, primary VZV infection usually occurs during the first decade of life. Twenty-eight VZV DNA-positive specimens were analyzed to identify VZV vaccine and wild-type genotypes. All analyzed specimens were wild type and the European (E) genotype.

Toward universal varicella-zoster virus (VZV) genotyping: diversity of VZV strains from France and Spain

Thirty-one isolates from France and Spain were genotyped using a published method analyzing DNA sequence variation in open reading frame (ORF) 22, together with an evaluation of three well-characterized single nucleotide polymorphisms (SNP) in ORF 38, 54, and 62. Nineteen were allocated to the European (E) genotype, six were mosaic-1 (M1), and two were mosaic-2 (M2). Four strains were assigned to a new genotype, mosaic-4 (M4). All isolates were wild type, with no Oka vaccine-associated markers. No isolates of the mosaic-3 (M3) or Japanese (J) genotype were observed. We also evaluated 13 selected isolates of E, J, M1, and M2 strains (9 of the 31 described above) using an alternative genotyping method based on the assessment of multiple SNP located in ORF 1, 9, 10, 21, 31, 50, 54, 62, and 68. This method assigns wild-type varicella-zoster virus (VZV) strains to seven genotypes: A1, A2, J1, B1, B2, C, and C1. VZV isolates identified as E (ORF22 method) had the genetic signature of genotype C VZV strains, M1 strains were A1, and M2 were A2. No J strains were detected, but parental Oka and vaccine Oka (genotype J) corresponded to genotype J1. M4 isolates (B) share the SNP array observed for M1 and E viruses, and probably represent recombinants between African-Asian (M1) and European (E) viruses. The two genotyping methods, using entirely different genomic targets, produced identical clusters for the strains examined, suggesting robust phylogenetic linkages among VZV strains circulating in Europe.

Review of varicella zoster seroepidemiology in India and Southeast Asia

Varicella zoster virus (VZV) predominantly affects children in temperate countries, with near-universal seroconversion occurring by late childhood. However, in tropical regions, VZV infection is common in adolescents and adults. This review identifies age-related VZV seroprevalence patterns in a number of Asian countries which indicate that seroconversion in tropical countries occurs at a later age than in temperate countries. Seasonal and regional variations in acute disease within some Asian countries suggest that temperate climates might favour transmission of the varicella virus, with incidence peaking during cooler months and in cooler, more temperate regions. VZV infection is often more severe in adults than in children, suggesting that tropical countries may be at risk of greater morbidity and mortality as a result of later-age seroconversion. Susceptibility of pregnant women and their infants, and of people infected with HIV/AIDS is also cause for concern. Vaccination may be beneficial in reducing the impact of VZV in Asian populations.