Summary

Chickenpox (varicella) is a highly contagious primary infection caused by varicella-zoster virus (VZV), a herpesvirus. It is characterised by a generalised vesicular rash (crops of vesicles in different stages) and is typically a mild, self-limiting illness in immunocompetent children. Complications include secondary bacterial skin infection (Group A Streptococcus, Staphylococcus aureus), pneumonitis, encephalitis, and cerebellar ataxia. Chickenpox is more severe in adults, pregnant women, neonates, and immunocompromised individuals. After primary infection, VZV remains latent in dorsal root ganglia and can reactivate later in life as herpes zoster (shingles). Prevention is through vaccination (live attenuated vaccine) and post-exposure prophylaxis with varicella-zoster immunoglobulin (VZIG) in high-risk contacts.

Key Facts

• Causative agent: Varicella-zoster virus (VZV) — Herpesviridae family
• Transmission: Respiratory droplets and direct contact with vesicle fluid; highly contagious
• Incubation period: 10-21 days (typically 14-16 days)
• Infectious period: 2 days before rash until all lesions crusted over (usually 5-7 days)
• Attack rate: >90% in susceptible household contacts
• Classic rash: "Dew drops on a rose petal" — vesicles on erythematous base
• Rash distribution: Centripetal (trunk → spreads to face, limbs); crops at different stages
• Complication rate: 2-5% in children; higher in adults and immunocompromised
• Latency: VZV dormant in dorsal root ganglia; reactivates as shingles
• Vaccine: Live attenuated; part of routine childhood immunisation in many countries

Clinical Pearls

"Starry Sky Rash": The hallmark of chickenpox is crops of vesicles at different stages of development (macules, papules, vesicles, crusts) — the "starry sky" appearance. This distinguishes it from monomorphic rashes.

"No NSAIDs": Avoid NSAIDs (ibuprofen) in chickenpox — associated with increased risk of secondary necrotising fasciitis. Use paracetamol only for fever.

"Adults Get Sicker": Chickenpox is generally mild in children but can be severe in adults, with higher rates of pneumonitis and hospitalisation. Adults should receive aciclovir if presenting within 24 hours.

"Pregnancy Alert": Chickenpox in pregnancy carries risks for mother (varicella pneumonitis) and fetus (congenital varicella syndrome in early pregnancy; severe neonatal varicella if infected around delivery).

"The Prodrome Is Non-Specific": Fever and malaise for 1-2 days before the rash is common. Don't dismiss non-specific symptoms in contacts of known cases.

Why This Matters Clinically

While chickenpox is usually benign in healthy children, it can be life-threatening in high-risk groups (immunocompromised, neonates, pregnant women). Recognising complications early (bacterial superinfection, pneumonitis, encephalitis) and knowing when to use antivirals is essential. Post-exposure prophylaxis with VZIG can prevent or modify disease in high-risk contacts.[1,2]

Skin Examination

Key Findings:

• Vesicles on erythematous base ("dew drop on rose petal")
• Lesions at different stages (macules, vesicles, crusts)
• Centripetal distribution (trunk > extremities)
• Mucosal ulcers (oral, conjunctival)
• Check for secondary infection (honey crusting, surrounding erythema)

Documentation:

• Approximate lesion count (mild <50, moderate 50-250, severe >250)
• Signs of bacterial superinfection
• Stage of lesions (all crusted = no longer infectious)

Systemic Examination (If Complications Suspected)

Outcomes in Healthy Children

Outcomes in High-Risk Groups

Key Guidelines

Landmark Studies

Varicella Vaccine Efficacy (Kuter et al. 1991)

• Demonstrated 95% efficacy in preventing varicella
• Foundation for routine childhood vaccination
• PMID: 1651974

NSAIDs and Necrotising Fasciitis (Lesko et al. 2001)

• Case-control study showing association between NSAIDs and NF in chickenpox
• Basis for avoiding ibuprofen
• PMID: 11178117

Evidence Strength

What is Chickenpox?

Chickenpox is a common and very contagious infection caused by the varicella-zoster virus. It causes an itchy rash of blisters that appear all over the body. Most children get it before age 10.

What are the symptoms?

• Fever and feeling unwell for 1-2 days
• Rash that starts as small red spots, then becomes blisters filled with fluid
• Blisters appear in waves — you'll see spots at different stages at the same time
• Very itchy
• Blisters eventually dry up and form scabs

How is it spread?

Chickenpox is very contagious. It spreads through:

• Coughs and sneezes (airborne droplets)
• Direct contact with blister fluid

A child is infectious from 2 days before the rash appears until all blisters have crusted over (usually 5-7 days).

How to treat it at home

• Give paracetamol (NOT ibuprofen) for fever and discomfort
• Use calamine lotion or cooling gels to soothe itching
• Give antihistamines (like Piriton) to help with itching
• Keep fingernails short and consider mittens at night
• Dress in loose, cool clothing
• Oatmeal baths can be soothing
• Keep your child hydrated

When to call a doctor

Seek medical advice if:

• High fever lasting more than 4 days
• Rash becomes very red, warm, or painful (infection)
• Difficulty breathing or persistent cough
• Unusual drowsiness, confusion, or headache
• Your child won't drink or is dehydrated
• Your child is very young (<1 year), immunocompromised, or unwell

High-Yield Exam Topics

Sample Viva Questions

Q1: A 5-year-old presents with an itchy vesicular rash. How do you manage this?

Model Answer: This is likely chickenpox in a healthy child. Diagnosis is clinical based on the typical rash (crops of vesicles at different stages, centripetal distribution). Management is supportive: paracetamol for fever (NOT NSAIDs due to necrotising fasciitis risk), antihistamines and calamine for itch, keep nails short. Advise parents the child is infectious until all lesions are crusted over (~5-7 days). No antivirals needed for a healthy child. I would ask about contacts who might be high-risk (pregnant women, immunocompromised, neonates) and advise accordingly.

Q2: Why should NSAIDs be avoided in chickenpox?

Model Answer: NSAIDs (particularly ibuprofen) have been associated with an increased risk of invasive Group A Streptococcal infection and necrotising fasciitis in children with chickenpox. Observational studies, including Lesko et al., demonstrated this association. The mechanism may involve masking early signs of infection, impairing neutrophil function, or direct effects on bacterial virulence. NICE and PHE guidelines recommend paracetamol only for symptomatic relief in chickenpox.

Q3: A pregnant woman at 10 weeks gestation is exposed to chickenpox. What is your management?

Model Answer: First, I would check her immunity status. If she has a history of chickenpox or is IgG positive, she is immune and no action is needed. If she is non-immune (IgG negative) and has been significantly exposed (same room for >15 minutes, face-to-face contact, same household), she is at risk of varicella and its complications (pneumonitis, and congenital varicella syndrome). I would administer VZIG as soon as possible (ideally within 10 days of exposure) to prevent or attenuate infection. If she develops varicella, treatment is with aciclovir (especially if ≥20 weeks), and she should be monitored closely for pneumonitis. Detailed fetal medicine follow-up is required for risk of congenital varicella syndrome, which is ~2% when infection occurs between weeks 13-20.

Common Exam Errors

Last Reviewed: 2025-12-24 | MedVellum Editorial Team

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.