Question
Varicella zoster infection
Answer
Varicella-Zoster Virus (VZV) is a member of the human herpesvirus family (HHV-3), a double-stranded DNA virus causing two distinct clinical diseases — a primary infection (varicella/chickenpox) and, following reactivation of established latent infection, herpes zoster (shingles).
Primary infection (Varicella/chickenpox): transmitted by respiratory droplets and direct contact with vesicle fluid, highly contagious; presents with fever and a characteristic generalized vesicular rash appearing in successive crops, so that lesions at different stages (macules, papules, vesicles, crusts) are present simultaneously (“dew drops on a rose petal” appearance, and a hallmark distinguishing feature from smallpox, in which lesions are typically synchronous/uniform in stage).
Latency and reactivation: after primary infection resolves, VZV establishes lifelong latency in dorsal root ganglia (sensory nerve ganglia); reactivation later in life (triggered by ageing, immunosuppression, stress) produces herpes zoster — a painful, vesicular rash confined to a single dermatome (unilateral, following the distribution of the affected sensory nerve), often preceded by localized pain/paraesthesia.
Complications: varicella — secondary bacterial skin infection, pneumonia (particularly in adults/immunocompromised), encephalitis/cerebellar ataxia, and, if acquired during pregnancy, congenital varicella syndrome or severe neonatal varicella if maternal infection occurs shortly before delivery; herpes zoster — post-herpetic neuralgia (persistent pain after rash resolution, particularly in the elderly), and, if involving the ophthalmic division of the trigeminal nerve, risk of ocular complications/vision loss.
Laboratory diagnosis: usually clinical; Tzanck smear of vesicle base scraping shows multinucleated giant cells (non-specific, cannot distinguish from HSV); PCR (the most sensitive/specific method) and direct fluorescent antibody testing on vesicle fluid; viral culture is slower and less sensitive.
Prevention and treatment: live attenuated varicella vaccine for primary prevention; a separate, more immunogenic recombinant zoster vaccine for preventing/reducing severity of shingles in older adults; acyclovir (or valacyclovir/famciclovir) for treatment of both varicella (in high-risk patients) and herpes zoster, most effective when started early in the course of illness.