New method of differentiating wild-type varicella-zoster virus (VZV) strains from Oka varicella vaccine strain by VZV ORF 6-based PCR and restriction fragment length polymorphism analysis.

A new method was developed to distinguish accurately wild-type varicella-zoster virus (VZV) strains from the Oka vaccine strain. Several DNA fragments covering open reading frame (ORF) 1-37 were amplified from wild-type VZV strains including the Oka parent strain and from the Oka vaccine strain. Restriction fragment length polymorphisms of these regions were compared, and nucleotide differences between the vaccine virus and other wild-type VZV strains were noted in ORFs 6, 10, and 35. In addition, variations of the R2 and R4 reiterated structures of the vaccine and its parent strains were examined. The Oka vaccine strain used in Japan was shown to be a mixture of viruses with different nucleotide sequences that had variations in at least three nucleotide positions in ORF 1-37 and had variable polymorphisms at R2 and R4 repeat regions (two and three patterns, respectively). The Oka parent strain on the other hand showed a single sequence and had only one reiterated structure at these regions. When VZV ORF 6 was amplified and its product was digested with AluI, the Oka vaccine strain could be precisely differentiated from its parent and from 56 other Japanese clinical isolates.