Herpes zoster is a clinical manifestation of the reactivation of latent varicella zoster virus infection. It is a cause of considerable morbidity, especially in elderly patients, and can be fatal in immunosuppressed or critically ill patients.erpes zoster is a clinical manifestation of the reactivation of latent varicella zoster virus infection. It is a cause of considerable morbidity, especially in elderly patients, and can be fatal in immunosuppressed or critically ill patients.