Question
Describe the pathogenesis and prophylaxis of Varicella Zoster virus infection
Answer
Pathogenesis of Varicella-Zoster Virus (VZV) infection
Primary infection (Varicella/chickenpox): transmitted via inhalation of infected respiratory droplets/aerosols or direct contact with vesicle fluid. The virus initially replicates in the nasopharyngeal mucosa and regional lymph nodes, followed by a primary viraemia seeding the reticuloendothelial system, and a secondary viraemia disseminating the virus to the skin, producing the characteristic generalized vesicular rash appearing in successive crops (giving the classical polymorphic pattern — lesions at different stages simultaneously — described as a “dew drop on a rose petal”). Following resolution of the primary infection, the virus establishes lifelong latency in the dorsal root ganglia (and cranial nerve ganglia).
Reactivation (Herpes zoster/shingles): with waning cell-mediated immunity (particularly in elderly or immunocompromised individuals), latent virus reactivates within a single sensory ganglion and travels along the corresponding sensory nerve to the skin, producing a localized, unilateral, dermatomal vesicular eruption, often accompanied by significant neuropathic pain, and can be complicated by post-herpetic neuralgia (persistent pain beyond lesion resolution).
Prophylaxis:
- Varicella vaccine — a live attenuated vaccine (Oka strain), given as a two-dose schedule (typically 12–15 months, with a second dose at 4–6 years), preventing primary varicella; reduces the future risk of herpes zoster by reducing wild-type virus exposure/reactivation burden.
- Herpes zoster (recombinant subunit) vaccine — a separate vaccine specifically for prevention of shingles/reactivation in older adults (typically ≥50 years), distinct from the primary childhood varicella vaccine, and does not carry the live-virus risks associated with the varicella vaccine.
- Varicella-Zoster Immunoglobulin (VZIG) — passive immunoprophylaxis for high-risk, non-immune individuals following significant exposure (e.g., immunocompromised patients, susceptible pregnant women, neonates of mothers with peripartum varicella).
- Antiviral prophylaxis/treatment — Acyclovir/Valacyclovir, used for treatment of active disease and, in specific high-risk exposure scenarios, as post-exposure prophylaxis.
- General infection control — isolation of infected/susceptible-exposed individuals (airborne and contact precautions), given the highly contagious nature of varicella.