An acute infectious, usually self-limited, disease believed to represent activation of latent varicella-zoster virus (herpesvirus 3, human) in those who have been rendered partially immune after a previous attack of chickenpox. It involves the SENSORY ganglia and their areas of innervation and is characterized by severe neuralgic pain along the distribution of the affected nerve and crops of clustered vesicles over the area. (From Dorland, 27th ed)