A patient presents with Bell's palsy-like facial paralysis accompanied by an ipsilateral vesicular rash (Ramsay Hunt syndrome). Which virus is responsible?

Ramsay Hunt syndrome (herpes zoster oticus) results from reactivation of latent varicella-zoster virus within the geniculate ganglion of the facial nerve, producing facial paralysis resembling Bell's palsy together with an ipsilateral vesicular rash (often involving the ear canal, auricle, and sometimes the oropharynx/palate).