Chickenpox Summary

Introduction

  • Acute disease caused by varicella-zoster virus
  • Vesicular rash with fever/malaise
  • Predominantly childhood illness
  • >90% of adults immune in England/Wales

Transmission

  • Highly infectious (90% susceptible contacts)
  • Personal contact/droplet spread
  • Incubation: 1-3 weeks
  • Infectious: 1-2 days before rash until crusting
  • Virus persists, can reactivate as shingles

Clinical Features

  • Prodrome: nausea, myalgia, anorexia, headache
  • Fever, malaise, feeding problems
  • Characteristic rash progression
  • Intensely itchy, appears in crops

Management

  • Admit if serious complications
  • Aciclovir for adults within 24h of rash
  • Symptomatic treatment
  • Avoid contact with high-risk groups

Complications

  • Children: usually self-limiting
  • Adults: more severe disease
  • Pregnancy: fetal varicella syndrome
  • Neonates: disseminated varicella

Post-Exposure

  • Assess exposure significance
  • Aciclovir first-line for at-risk
  • VZIG for contraindications
  • Specialist advice for high-risk

Chickenpox

Acute disease caused by varicella-zoster virus

Introduction

Chickenpox is an acute disease caused by varicella-zoster virus. It is characterised by a vesicular rash, often preceded by fever and malaise. Chickenpox is predominantly a childhood illness; its incidence is highest before 10 years of age.

Immunity Statistics

As chickenpox is a common childhood disease, more than 90% of people older than 15 years of age in England and Wales are immune (seropositive for varicella-zoster immunoglobulin G).

Transmission

Infectivity

  • Varicella is very infectious; up to 90% of susceptible contacts develop the disease
  • Transmission by personal contact or droplet spread
  • Incubation period of 1–3 weeks

Infectious Period

  • Infectious from 1–2 days before rash appears
  • Until vesicles are dry/crusted over (usually 5 days after rash onset)
  • Longer period in immunocompromised people

Virus Persistence

  • Virus persists in sensory nerve root ganglia after infection
  • Can reactivate years later as herpes zoster (shingles)
  • Can get chickenpox from exposure to shingles
  • Cannot get shingles from exposure to chickenpox

Clinical Features

In most cases, the diagnosis can be made clinically from the characteristic chickenpox rash. If there is doubt, a history of recent exposure to chickenpox (or shingles), or cases occurring in close contacts, may help confirm the diagnosis.

Systemic Symptoms

  • Prodrome: nausea, myalgia, anorexia, headache (adolescents/adults)
  • General malaise, loss of appetite, feeding problems
  • Fever

Characteristic Rash

  • Small, erythematous macules on scalp, face, trunk, proximal limbs
  • Progress to papules, clear vesicles (intensely itchy), pustules
  • Vesicles on palms, soles, mucous membranes
  • Painful oral or genital ulcers
  • Vesicles appear in crops with different stages
  • Crusting within 5 days, crusts fall off after 1–2 weeks

Differential Diagnosis

Vesicular Viral Rashes

  • Herpes simplex (not usually disseminated)
  • Herpes zoster (unilateral, dermatomal)
  • Hand, foot, and mouth disease (Coxsackie virus)

Other Infections

  • Impetigo
  • Scabies
  • Syphilis
  • Meningococcaemia (confused with haemorrhagic varicella)
  • Toxic shock syndrome

Skin Disorders

  • Guttate psoriasis
  • Drug eruption
  • Insect bites
  • Papular urticaria
  • Erythema multiforme
  • Stevens-Johnson syndrome
  • Henoch-Schönlein purpura
  • Dermatitis herpetiformis

Management

Hospital Admission

Admit to hospital if serious complications suspected: pneumonia, encephalitis, dehydration, or severe secondary bacterial skin infection.

Antiviral Treatment

  • Oral aciclovir 800 mg 5 times daily for 7 days
  • For immunocompetent non-pregnant adults/adolescents (≥14 years)
  • Must present within 24 hours of rash onset
  • Particularly for severe chickenpox or high-risk individuals (smokers)
  • Not recommended for otherwise healthy children

Symptomatic Treatment

  • Paracetamol for pain/fever (avoid NSAIDs)
  • Topical calamine lotion for itch
  • Chlorphenamine for itch (≥1 year old)

Patient Advice

  • Most infectious: 1–2 days before rash appears
  • Infectivity continues until all lesions crusted over (~5 days)
  • Avoid contact with:
    • Immunocompromised people
    • Pregnant women
    • Infants ≤4 weeks
  • Children should stay away from school/nursery until all vesicles crusted

Complications

Children

  • Usually self-limiting, complications rare
  • Skin bacterial superinfection (impetigo, cellulitis, necrotising fasciitis)
  • Neurological complications (Reye's syndrome, cerebellar ataxia, encephalitis)
  • Rare: myocarditis, glomerulonephritis, pancreatitis, arthritis

Adults

  • More serious than in children
  • Higher hospitalization rates
  • Pneumonia, hepatitis, encephalitis
  • Shingles from reactivation of latent infection

Pregnancy

  • Severe chickenpox, increased risk of varicella pneumonia
  • First 28 weeks: risk of fetal varicella syndrome
    • Skin scarring in dermatomal distribution
    • Eye defects (microphthalmia, chorioretinitis, cataracts)
    • Limb hypoplasia
    • Neurological abnormalities

Neonates

  • Increased risk of disseminated/haemorrhagic varicella
  • Mother infected 1–4 weeks before delivery: up to 50% babies infected
  • ~25% develop clinical varicella of the newborn

Post-Exposure Prophylaxis

Initial Assessment

For all people with history of exposure to chickenpox, establish:

  • Certainty of chickenpox diagnosis in contact
  • Significance of exposure
  • History of previous chickenpox
  • Risk of complications (pregnant, immunocompromised, neonates)
  • Contact with high-risk others (healthcare workers)

Defining Significant Exposure

Type of Infection

  • Chickenpox
  • Disseminated shingles
  • Immunocompetent with exposed shingles lesions
  • Immunocompromised with localized shingles

Timing of Exposure

  • Chickenpox: 48h before rash to crusting
  • Disseminated shingles: 48h before rash to crusting
  • Localized shingles: day of rash onset to crusting

Closeness/Duration

  • Maternal/neonatal contact
  • Continuous home contact
  • Same room for ≥15 minutes
  • Face-to-face contact (conversation)

Assessing Susceptibility

Immunocompetent Individuals

  • History of chickenpox, shingles, or 2 vaccine doses = immunity
  • No history: urgent antibody testing
  • PEP if VZV IgG <100 mIU/ml

Immunosuppressed Patients

  • History not reliable indicator
  • Check VZV antibody levels urgently
  • PEP if VZV IgG <150 mIU/ml or negative/equivocal

Management Recommendations

Healthy Immunocompetent

  • Not significant exposure or immune: reassure
  • Not immune: advise may develop chickenpox

Healthcare Workers

  • Definite history: can continue working
  • If rash/fever/unwell: seek occupational health advice
  • No history/vaccination: avoid high-risk patients for 8-21 days

Pregnant Women

  • Definite history: reassure immune
  • No history + significant contact: urgent specialist advice
  • Test for VZV IgG antibodies
  • Negative antibodies: discuss prophylaxis with specialist

Neonates

  • Determine timing of maternal infection relative to delivery
  • Urgent specialist advice for testing/management
  • Discuss breastfeeding if mother has chickenpox

Immunocompromised

  • Same-day specialist advice

Post-Exposure Prophylaxis

Aciclovir [unlicensed use] recommended first-line for at-risk individuals, except for certain susceptible neonates and those with contraindications to antivirals, where varicella-zoster immunoglobulin (VZIG) is recommended instead.