Which herpesvirus is most commonly associated with reactivation in the form of dermatomal vesicular rash and is transmitted by respiratory droplets during primary infection?

Explanation

## Varicella-Zoster Virus: Primary Infection and Reactivation **Key Point:** VZV causes varicella (chickenpox) as primary infection and herpes zoster (shingles) as reactivation. The reactivation characteristically presents as a dermatomal vesicular rash following a dermatome distribution. ### VZV Epidemiology and Transmission **Primary Infection (Varicella):** - Transmitted via respiratory droplets or direct contact with vesicular fluid - Highly contagious (R₀ ~10–12 before vaccination) - Incubation period: 10–21 days - Presents with fever, malaise, followed by centripetal vesicular rash ("crops") **Reactivation (Herpes Zoster):** - Occurs when latent virus in dorsal root ganglia reactivates - Presents as painful vesicular rash in a single dermatome (dermatomal distribution) - Risk increases with age (>50 years), immunosuppression, malignancy - Preceded by prodromal pain, paresthesia, or hyperesthesia in the affected dermatome ### Comparison of Herpesvirus Reactivation Patterns | Virus | Primary Infection | Reactivation Pattern | Transmission Route (Primary) | |-------|-------------------|----------------------|------------------------------| | **VZV** | Varicella (disseminated rash) | Herpes zoster (dermatomal) | Respiratory droplets | | **HSV-1** | Gingivostomatitis, pharyngitis | Oral/labial herpes (localized) | Respiratory droplets, saliva | | **HSV-2** | Genital herpes | Genital herpes (localized) | Sexual contact | | **CMV** | Asymptomatic or mononucleosis-like | Viremia, visceral disease | Saliva, urine, sexual contact | | **EBV** | Infectious mononucleosis | Asymptomatic shedding (rare reactivation) | Respiratory droplets, saliva | **High-Yield:** VZV reactivation as herpes zoster is the ONLY herpesvirus that presents with a **dermatomal** (single dermatome) distribution. This is a pathognomonic feature and a frequent NEET PG question. **Clinical Pearl:** The dermatomal distribution of zoster follows the path of the affected sensory nerve and dorsal root ganglion. Thoracic dermatomes (T5–L2) account for ~50% of cases; ophthalmic division of trigeminal nerve (V1) accounts for ~10–15% (herpes zoster ophthalmicus). **Mnemonic:** **VZVD** — VZV = Varicella (primary) + Zoster (reactivation) + Dermatomal distribution. **Warning:** Do not confuse HSV reactivation (which is localized to the lips or genitals but NOT dermatomal) with VZV reactivation (which is strictly dermatomal). HSV recurs in the same anatomical site due to latency in sensory ganglia innervating that site, but the rash is not dermatomal.