Both diseases are caused by varicella‑zoster virus (VZV), a human alphaherpesvirus. They represent primary infection and reactivation, respectively.
Varicella (Chickenpox)
- Primary infection — usually childhood.
- Highly contagious (respiratory droplets, vesicle fluid).
- Prodrome: fever, malaise → pruritic vesicular rash (centripetal distribution).
- Self‑limited in immunocompetent; complications: bacterial superinfection, pneumonia, encephalitis, Reye's syndrome (with aspirin).
- Virus establishes latency in dorsal root/cranial nerve ganglia.
Herpes Zoster (Shingles)
- Reactivation of latent VZV — typically decades later.
- Triggered by waning cell‑mediated immunity (aging, immunosuppression, stress).
- Unilateral dermatomal rash (thoracic > lumbar > cervical), pain/paresthesia preceding rash.
- Complications: postherpetic neuralgia (PHN), ophthalmicus (vision threat), Ramsay Hunt (facial nerve), myelitis.
- Contagious: can cause varicella in susceptible contacts via vesicle fluid.
Prevention
- Varicella vaccine (live attenuated): 2‑dose childhood series; >90% effective.
- Zoster vaccine (RZV, recombinant): ≥50 years (or ≥19 if immunocompromised); >90% efficacy against shingles/PHN.
Treatment
- Antivirals (acyclovir, valacyclovir, famciclovir) within 72 hrs of rash onset ↓ severity/duration.
- Corticosteroids for severe inflammation (controversial).
- PHN: gabapentinoids, TCAs, topical lidocaine/capsaicin.
Understanding the shared etiology clarifies why vaccination against one protects against both.
