Chicken Pox

Overview – Chicken Pox

Chicken pox, or varicella, is a highly contagious viral illness caused by the varicella-zoster virus (VZV), a member of the herpesvirus family. It typically affects children under 10 and presents with a distinctive vesicular rash and systemic symptoms like fever and malaise. Most individuals gain lifelong immunity following infection, although the virus may remain dormant and reactivate later in life as herpes zoster (shingles). Understanding the transmission, progression, and complications of chicken pox—particularly during pregnancy—is crucial for clinical practice.

Definition

Chicken pox is a primary infection caused by the varicella-zoster virus (VZV, also known as human herpesvirus 3). It is characterised by widespread vesicular eruptions on the skin and mucous membranes and is typically self-limiting in children.

Aetiology

• Caused by the varicella-zoster virus (VZV)
• Member of the Herpesviridae family (HHV-3)

Transmission

• Highly contagious
• Spread via:
  • Aerosolised respiratory droplets
  • Direct contact with fluid from vesicular lesions
• Peak transmission: 1–2 days before rash onset until all lesions are crusted over

Pathophysiology

• Incubation period: ~14 days
• Primary infection (chicken pox):
  • Initial mucosal infection (nasopharynx)
  • Viral replication → viremia → epidermal invasion
• Latency:
  • Virus lies dormant in dorsal root ganglia of sensory nerves
• Reactivation (shingles):
  • Can occur decades later as a painful, dermatomal rash

Clinical Features

• Rash:
  • Itchy, erythematous macules → papules → vesicles → pustules → crusts
  • Begins on trunk, spreads to face and limbs
  • Lesions at different stages simultaneously (“crops” of lesions)
• Systemic symptoms:
  • Fever
  • Headache
  • Malaise
  • Nausea/vomiting
  • Diarrhoea

Investigations

• Clinical diagnosis is usually sufficient
• Confirmatory tests (if required):
  • Direct immunofluorescence
  • VZV-specific serology:
    • IgM: recent/primary infection
    • IgG: past exposure or immunity

Management

• Supportive care:
  • Antipyretics (e.g. paracetamol)
  • Antihistamines for itch
  • Calamine lotion or oatmeal baths
• Antivirals (e.g. aciclovir) may be used in:
  • Immunocompromised patients
  • Severe disease
  • Pregnant women
  • Adults with primary infection

Complications

General:

• Secondary bacterial infection of lesions
• Pneumonia (especially in adults)
• Encephalitis
• Hepatitis

Pregnancy-Associated:

• Congenital Varicella Syndrome:
  • Occurs if maternal infection in first trimester (risk ~3-8%)
  • Associated complications:
    • Skin: cicatricial scarring, hypopigmentation
    • Neurological: intrauterine encephalitis, seizures, developmental delay
    • Ocular: cataracts, chorioretinitis, anisocoria
    • Musculoskeletal: limb hypoplasia
    • Systemic: cortical atrophy, renal anomalies (hydronephrosis, hydroureter), GORD, congenital heart defects
• Perinatal Varicella:
  • If maternal infection occurs 5 days before to 2 days after birth
  • Neonatal infection can be severe
  • Mortality rate up to 30%

Summary – Chicken Pox

Chicken pox (varicella) is a highly contagious viral illness caused by varicella-zoster virus, most commonly affecting children. It presents with a generalised vesicular rash, systemic symptoms, and confers lifelong immunity. However, the virus may remain dormant and reactivate as shingles. Complications are rare in children but significant in adults and pregnant women. For broader context, see our Skin & Dermatology Overview page.