Varicella-zoster virus (human herpesvirus 3; VZV) is one of eight herpes viruses 
that routinely infect humans. It is classified as a member of the genus 
Varicellovirus, subfamily Alphaherpesvirinae, family Herpesviridae. Of the other 
human herpes viruses it is most closely related to the herpes simplex viruses 
(also members of the Alphalerpesvirinae). Like all herpes viruses, the virus has 
a large double-stranded DNA genome within an icosahedral nucleocapsid. This is 
surrounded by a proteinaceous tegument and a trilaminar membrane derived from 
host-cell membranes into which the viral glycoproteins are inserted. The 
structure of the virion is summarized in Fig. 1.