Zoster

Zoster, or herpes zoster, is a viral disease caused by reactivation of varicella-zoster virus (VZV), the same virus that causes chickenpox. After a varicella infection resolves, VZV remains latent in sensory nerve ganglia and can reactivate months or years later. Risk increases with age and immune suppression (for example HIV infection, cancer, or immunosuppressive therapy).

Reactivation produces a painful, vesicular rash in a dermatomal distribution, usually on one side of the body. Prodromal pain, itching, or tingling may precede the rash by a few days. Involvement of the ophthalmic division of the trigeminal nerve can threaten vision; involvement of the facial nerve can cause Ramsay Hunt syndrome.

Diagnosis is mainly clinical; laboratory tests such as PCR on lesion samples may be used in atypical cases or in immunocompromised patients.

Treatment should be started promptly with antiviral therapy (acyclovir, valacyclovir, or famciclovir), ideally within 72 hours of rash onset. Pain control is important; some patients may benefit from corticosteroids, though evidence is mixed. Complications include postherpetic neuralgia, which may require long-term pain management.

Prevention relies on vaccination. The recombinant zoster vaccine (Shingrix) is recommended for adults 50 and older, with high efficacy against shingles and postherpetic neuralgia. The older live attenuated vaccine (Zostavax) is less commonly used in many regions. Most people recover within 2-4 weeks, but postherpetic neuralgia can persist for months or years, especially in older adults.