Analysis of numbers of repeated units in R2 region among varicella-zoster virus strains

Background: A variable region, R2, on the varicella–zoster virus (VZV) genome contains a repeated 42-bp unit. Objective: The purpose of this study is the derivation of significance from tandem reiteration structure in the R2 region. Methods: Fifty-two specimens were collected from 52 patients with herpes zoster in Osaka and Tokyo, Japan. After treatment of the specimens to release viral DNA, the samples were amplified directly by polymerase chain reaction. In addition, 14 samples were collected from 7 of these zoster patients after valaciclovir or aciclovir therapy. Results: Analyses of the 52 specimens revealed that the number of repeats ranged from 4 to 13. Interestingly, the numbers of repeats among various VZV strains showed a normal distribution pattern, so that 6–9 repeats were found to be predominant in both Osaka (85%) and Tokyo (72%). The pre- and post-treatment strains taken from the same individuals showed the same numbers of repeats (7–9 in 6 cases and 11 in one). Conclusion: Our results suggest that the 6–9 repetitions of the 42-bp unit, with presumed stability, may offer these virus strains an advantage in virulence to human skin.