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Shingles, or herpes zoster, is a painful skin rash with blisters that, characteristically, occurs in a stripe limited to just one side of the body. The rash usually heals within 2–5 weeks, but around one in five people experience residual nerve pain for months or years.

Shingles is caused by varicella zoster virus (VZV), an alpha-herpesvirus. Initial VZV infection usually occurs in childhood causing chickenpox. After this resolves, the virus is not eliminated from the body, but remains latent in the nerve cell bodies of the dorsal root or trigeminal ganglia, without causing symptoms. Years or decades later, shingles occurs when virions in a single ganglion reactivate, travel down nerve fibres and infect the skin around the nerve. The shingles rash is restricted to the area of skin supplied by a single spinal nerve, termed the dermatome. Exactly how VZV remains latent in the body, and subsequently reactivates, is unclear.

Around a third of the population will develop shingles. Repeated episodes are rare. In the United States, about half the cases occur in people aged 50 years or older. Vaccination at least halves the risk, and prompt treatment with aciclovir or related antiviral drugs can reduce the severity and duration of the rash.