Zoster

Herpes zoster is caused by reactivation of latent varicella-zoster virus (VZV), a neurotropic human alphaherpesvirus, following primary varicella infection and lifelong latency in sensory and autonomic ganglia ^[1][4][2][5]. The condition presents as localized painful skin blistering rash containing infectious virus upon reactivation ^[4][2].

The disease classically shows a painful unilateral vesicular eruption usually confined to a single dermatome, often preceded by malaise, headache, low-grade fever, and abnormal skin sensations for two to three days ^[2][3]. The rash progresses from maculopapular lesions to clear vesicles that cloud and crust over within seven to ten days ^[3]. Documented complications include postherpetic neuralgia, herpes zoster ophthalmicus, Ramsay Hunt syndrome, acute retinal necrosis, vasculitis, and renal or gastrointestinal involvement ^[1][2][5].

Herpes zoster occurs secondary to varicella and its incidence increases with age, being rare in children and young people except when linked to metabolic or neoplastic disorders ^[1]. In the United States an estimated 1 million cases occur each year with a 30% individual lifetime risk, and persons with reduced cell-mediated immunity are 20 to 100 times more likely to develop the condition ^[3]. In Singapore most adults remain at risk because varicella immunization was only introduced in 2020 ^[2].

Reactivation of VZV causes herpes zoster characterized by a localized painful blistering rash containing infectious virus, though the provided evidence describes cutaneous viral shedding rather than quantified person-to-person spread ^[4]. Primary varicella lesions spread cell-free virus to cause further cases and infect sensory nerve endings, establishing latency that later may reactivate as zoster ^[4].

Two vaccines against herpes zoster are available for healthy older adults: a live attenuated VZV vaccine and a recombinant adjuvanted glycoprotein E subunit vaccine, the latter also permissible in severely immunosuppressed patients ^[1]. The recombinant zoster vaccine has shown high efficacy, and advisory bodies recommend vaccination for adults from age 50 or 60 years depending on jurisdiction ^[2][3]. In Singapore, given recent introduction of varicella immunization, clinician awareness and vaccine use are emphasized for at-risk adults ^[2].

1. 1 Patil A et al. Herpes zoster: A Review of Clinical Manifestations and Management. Viruses. 2022 Jan 19. PMID: 35215786. doi: 10.3390/v14020192. PubMed: https://pubmed.ncbi.nlm.nih.gov/35215786/
2. 2 Lim DZJ et al. Herpes Zoster and Post-Herpetic Neuralgia-Diagnosis, Treatment, and Vaccination Strategies. Pathogens. 2024 Jul 17. PMID: 39057822. doi: 10.3390/pathogens13070596. PubMed: https://pubmed.ncbi.nlm.nih.gov/39057822/
3. 3 Saguil A et al. Herpes Zoster and Postherpetic Neuralgia: Prevention and Management. Am Fam Physician. 2017 Nov 15. PMID: 29431387. PubMed: https://pubmed.ncbi.nlm.nih.gov/29431387/
4. 4 Tommasi C et al. The Biology of Varicella-Zoster Virus Replication in the Skin. Viruses. 2022 May 6. PMID: 35632723. doi: 10.3390/v14050982. PubMed: https://pubmed.ncbi.nlm.nih.gov/35632723/
5. 5 Gershon AA et al. Varicella zoster virus infection. Nat Rev Dis Primers. 2015 Jul 2. PMID: 27188665. doi: 10.1038/nrdp.2015.16. PubMed: https://pubmed.ncbi.nlm.nih.gov/27188665/