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

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Abstract
The incidence of varicella in Singapore has been increasing since 1984. In 1991,17,930 cases were reported in a population of about 3 million. A serological survey completed in 1990 demonstrated that only 43% of the cohort had antibodies to varicella‐zoster virus (VZV), indicating inadequate herd immunity. To exclude novel VZV strains, representative VZV isolates from 9 chicken pox and 4 zoster patients were characterised by restriction endonuclease analysis. DNAs were extracted from viral isolates propagated in MRC5 human embryo lung cells and were digested separately with Bg/ll, EcoRI, Pstl, Sall, and Xbal enzymes. The cleavage profiles of these VZV strains derived from both chicken pox and zoster lesions revealed no distinct differences. This observation implies that the current upsurge of chicken pox most likely stems from closely related VZV genotypes infecting a susceptible population with insufficient herd immunity. Comparison of the restriction fragments of the Singapore and the Dumas strains revealed polymorphisms of the Sal/I‐D, SaI/l‐E, and Xbal‐l fragment lengths, which correlated with variable regions I, II, and Ill of the VZV genome, thereby representing geographically distinct genotypic variants of VZV.