Varicella-Zoster Virus — UKMLA Guide 2026

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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.

Key points

Chickenpox (varicella): primary VZV infection — fever + generalised vesicular rash (lesions in different stages: macules, papules, vesicles, crusts). Usually benign in children, severe in adults/immunocompromised/pregnancy
Shingles (herpes zoster): reactivation of latent VZV in dorsal root ganglion — UNILATERAL dermatomal vesicular rash with preceding pain. Does NOT cross the midline
Chickenpox in adults/immunocompromised: oral aciclovir 800 mg 5 times daily for 7 days (if within 24h of rash). IV aciclovir if severe or immunocompromised
Shingles: oral aciclovir 800 mg 5 times daily for 7 days or valaciclovir 1g TDS for 7 days — most effective if started within 72 hours of rash onset
Post-herpetic neuralgia (PHN): pain persisting >90 days after shingles rash. Treat with amitriptyline, gabapentin, or pregabalin. Prevented by Shingrix vaccine (offered to adults aged 70-79 in UK)

Overview

Varicella-zoster virus (VZV) is a herpesvirus that causes two distinct clinical syndromes. Primary infection (chickenpox/varicella) is a highly contagious childhood illness characterised by a generalised vesicular rash. After primary infection, VZV establishes latency in dorsal root ganglia and can reactivate years later as herpes zoster (shingles) — a painful unilateral dermatomal vesicular eruption. Shingles is more common in the elderly and immunosuppressed due to waning T-cell immunity.

Epidemiology

Chickenpox is extremely common — >90% of UK adults are seropositive. It is usually mild in children but can be severe in neonates, adults, pregnant women, and immunocompromised individuals. Herpes zoster affects approximately 1 in 4 people over their lifetime, with incidence rising sharply after age 50. Post-herpetic neuralgia affects ~10-20% of shingles patients overall, but up to 50% of those >60 years.

Clinical Features

Symptoms

Chickenpox: fever, malaise, then generalised pruritic vesicular rash ("dewdrop on a rose petal" — vesicle on erythematous base). Lesions in DIFFERENT STAGES (crops)

Shingles: prodromal pain/burning/tingling in dermatomal distribution (1-5 days before rash)

Shingles rash: unilateral dermatomal grouped vesicles on erythematous base — does NOT cross the midline

Severe pain with the rash (can be debilitating in elderly)

Ophthalmic zoster (V1 — trigeminal): vesicles on forehead/nose tip (Hutchinson sign = nasociliary nerve involvement = high risk of ocular complications)

Signs

Chickenpox: generalised centripetal rash (trunk > limbs), lesions at different stages

Shingles: unilateral dermatomal vesicles — most commonly thoracic dermatomes (T3-L2)

Hutchinson sign: vesicles on tip of nose → nasociliary branch of V1 → risk of keratitis, uveitis

Ramsay Hunt syndrome: shingles of the geniculate ganglion → vesicles in ear canal + facial nerve palsy + hearing loss/vertigo

Investigations

First-line

Clinical diagnosisBoth chickenpox and shingles are usually diagnosed CLINICALLY — typical rash appearances are distinctive

VZV PCR (vesicle fluid swab)If diagnostic uncertainty — confirms VZV. Also useful in immunocompromised or atypical presentations

Second-line

VZV IgG serologyTo determine immunity status — important in pregnant contacts or healthcare workers with uncertain chickenpox history

Specialist

Ophthalmology reviewUrgent if ophthalmic zoster (V1) — slit-lamp examination for keratitis, anterior uveitis

Management

NICE CKS + PHE/UKHSA Green Book

Chickenpox

Children (immunocompetent): usually self-limiting. Calamine lotion, antihistamines for itch, paracetamol (AVOID ibuprofen — possible increased risk of necrotising fasciitis)
Adults, pregnant women, immunocompromised: oral aciclovir 800 mg 5 times daily for 7 days if within 24 hours of rash onset
Severe/disseminated (immunocompromised): IV aciclovir 10 mg/kg TDS
Infectious from 2 days before rash until all lesions have crusted (usually 5-7 days)

Shingles

Antiviral: aciclovir 800 mg 5 times daily for 7 days OR valaciclovir 1g TDS for 7 days — start within 72 hours of rash onset for best effect
Analgesia: paracetamol, NSAIDs, consider early neuropathic pain agents (amitriptyline, gabapentin) if pain is severe
Calamine lotion, non-adherent dressings for rash comfort
Ophthalmic zoster: same antiviral doses + URGENT ophthalmology referral
Ramsay Hunt: same antivirals + oral prednisolone (consider, though evidence is limited) + ENT/neurology referral

Post-herpetic neuralgia (PHN)

First-line: amitriptyline 10-25 mg ON (titrate up) or gabapentin/pregabalin
Second-line: topical capsaicin cream 0.075% or lidocaine 5% plasters
PHN can be extremely distressing — may last months to years in elderly

Chickenpox in pregnancy

Chickenpox in pregnancy is potentially DANGEROUS: risk of varicella pneumonia (10% mortality), foetal varicella syndrome (limb abnormalities, eye defects, skin scarring — first 20 weeks)
If non-immune pregnant woman exposed to chickenpox: VZIG (varicella-zoster immunoglobulin) within 10 days of exposure
If chickenpox develops: oral aciclovir (safe in pregnancy)

Shingles vaccination (Shingrix)

Shingrix (recombinant adjuvanted vaccine): offered to adults aged 70-79 in UK national programme
>90% efficacy against shingles and ~90% against PHN — far superior to previous live Zostavax vaccine
Two doses, 2-6 months apart. Can be given to immunocompromised (unlike live vaccine)

Complications

Post-herpetic neuralgia: The most common complication of shingles — risk increases with age
Ophthalmic zoster: Keratitis, anterior uveitis, secondary glaucoma — can cause visual loss
Ramsay Hunt syndrome: Facial nerve palsy + ear vesicles — poorer prognosis than Bell palsy
Varicella pneumonia: Serious complication in adults, smokers, and pregnancy — can cause ARDS
Secondary bacterial skin infection: Group A Strep or Staph aureus — cellulitis, necrotising fasciitis (rare)
Disseminated zoster: In immunocompromised — multi-dermatomal, visceral involvement, high mortality

UKMLA Exam Tips

1Shingles does NOT cross the midline — if bilateral, think disseminated VZV in immunocompromised
2Hutchinson sign (nose tip vesicles) = V1 (nasociliary nerve) = high risk of eye involvement → urgent ophthalmology
3Ramsay Hunt = facial nerve palsy + ear vesicles + deafness ± vertigo — VZV reactivation in geniculate ganglion
4Chickenpox: AVOID ibuprofen/NSAIDs in children (possible necrotising fasciitis risk). Use paracetamol only
5Non-immune pregnant woman exposed to chickenpox → VZIG within 10 days. Chickenpox in pregnancy = risk of varicella pneumonia
6Shingrix vaccine >90% effective — offered at age 70 in UK. Can be given to immunocompromised (recombinant, not live)

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