Varicella – zoster virus remains dormant in the:

Correct Answer: A. Dorsal root ganglion

Varicella-zoster virus (VZV) is a neurotropic herpesvirus that establishes latency in sensory ganglia, specifically the dorsal root ganglia (DRG) and cranial nerve ganglia. After primary infection (chickenpox), the virus travels retrogradely along sensory nerve axons to reach the DRG, where it remains dormant in the nuclei of sensory neurons. This latent infection can persist for decades without causing symptoms. Reactivation occurs when cell-mediated immunity wanes—typically in elderly patients, immunocompromised individuals, or those with malignancy—leading to herpes zoster (shingles). The dermatomal distribution of zoster lesions directly corresponds to the sensory innervation territory of the affected DRG, which is the anatomical basis for the characteristic unilateral, band-like rash. In Indian clinical practice, zoster is common in elderly patients and those with tuberculosis or HIV; the DRG latency explains why antiviral prophylaxis (acyclovir) is recommended for immunocompromised patients to prevent reactivation. Understanding DRG latency is critical for explaining post-herpetic neuralgia (PHN), a major complication in Indian populations, where viral reactivation causes inflammation and nerve damage.

Why the other options are wrong

B. Medulla oblongata — This is wrong because the medulla oblongata is part of the brainstem and is not a site of VZV latency. While VZV can cause CNS complications (encephalitis, meningitis), the virus does not establish persistent latency in the medulla. This option confuses CNS involvement with the primary latency site. VZV latency is specifically in peripheral sensory ganglia, not central nervous system structures. C. Ventral root — This is wrong because ventral roots contain motor nerve fibers, and VZV establishes latency in sensory neurons, not motor neurons. The virus travels retrogradely along sensory (dorsal) axons to reach the DRG. Ventral roots do not contain the sensory neuron cell bodies where latency occurs. This option exploits confusion between dorsal (sensory) and ventral (motor) spinal roots. D. Skin — This is wrong because while VZV replicates in skin during acute infection (chickenpox) and reactivation (zoster), the virus does not remain dormant in skin. After primary infection, infectious virus is cleared from skin, and latency is established only in neural tissue. Skin is the site of clinical manifestation, not viral latency. This option confuses the site of disease expression with the site of dormancy.

High-Yield Facts

Mnemonics

DRG = Dormancy Reservoir for Ganglia Dorsal Root Ganglion is where VZV sleeps. Remember: Dorsal = Dormancy. Sensory neurons in DRG → latency site. Ventral roots are motor—VZV ignores them. ZOSTER = Zonal Eruption from Reactivated Sensory Ganglia Zoster always follows a dermatomal (single nerve root) distribution because the virus reactivates from one DRG at a time. This anatomical link is the key to understanding why zoster is unilateral and band-like.

NBE Trap

NBE pairs "skin" as a distractor because students confuse the site of viral replication (skin during acute infection) with the site of viral latency (DRG). The question tests whether students understand the pathophysiology of herpesvirus latency, not just clinical presentation.

Clinical Pearl

In Indian clinical practice, an elderly patient with unilateral dermatomal pain followed by vesicular rash is classic zoster. The pain often precedes the rash by 2–3 days (prodrome), reflecting viral reactivation in the DRG before reaching skin. This is why early antiviral therapy (within 72 hours) and pain management are critical to reduce PHN risk in our aging population.

_Reference: Robbins Ch. 8 (Infectious Diseases); Harrison Ch. 187 (Herpes Simplex and Varicella-Zoster Infections)_