Chicken Pox

Highly infectious acute disease caused by the varicella-zoster virus, characterised by an itchy rash and often accompanied by fever and malaise.


  • Varicella is highly infectious (up to 90% of susceptible contacts contract chicken pox)
    • Infectious from 1-2 days prior to rash until the lesions are dry/crusted over (usually around 5-6 days after symptom onset)
  • Mainly found in children under 10, and is very common (1 in 100)
  • The virus  has an incubation period of around 4-6 days (til viraemia- and 8-14 days til rash)


  • There is usually a prodromal viraemia that causes nausea, malaise, myalgia, anorexia, mild abdominal pain, headache and fever.
  • Rash
    • Appears in ‘crops’ and has a classical lifespan (i.e. different crops may appear at different stages)
    • Small, erythematous macules first appear, which develop through papule, vesicle, pustule and crust (when the crust falls off, there may also be a mark left for a week or so)
      • Usually found on the face, neck and trunk.  The limbs are less severely affected

Complications and Special Cases

  • Children
    • Usually self-limiting, but bacterial superinfection (e.g. impetigo, cellulitis) can occur.  Increased temperature, erythema and tenderness (often after initial improvement) are signs of infection.
  • Adults
    • Older children, adolescents and adults are more likely to have severe disease, with a longer course.  They are also more likely to develop complications e.g.
      • Varicella pneumonia- particularly if they smoke
      • Viral encephalitis, benign cerebellar ataxia and vasculitis may also be caused by varicella zoster
      • Reactivation of Varicella-zoster to cause Shingles may also occur
  • Pregnancy
    • Risk to mother
      • Pregnant women are at high risk of severe disease and varicella pneumonia (up to 1 in 10), as well as other complications.  It has a mortality of 1%.
    • Risk to the foetus
      • No apparent increased risk of miscarriage in the first trimester
      • Increased risk of foetal varicella syndrome if infected before 28 weeks
        • Skin scarring in the dermatomal distribution
        • Eye defects (microphthalmia, chorioretinitis, cataracts)
        • Hypoplasia of the limbs
        • Neurological abnormalities (microcephaly, cortical atrophy, learning difficulties, dysfunction of the bowel/bladder sphincters)
    • Risk to the neonate
      • If the mother is infected 1-4 weeks before birth, up to half of babies will be infected and up to a quarter will develop clinical symptoms
      • neonates are at higher risk of disseminated or haemorrhagic disease
  • Immunocompromised people
    • At risk of severe, disseminated disease with multi-organ involvement (pneumonia, encephalitis, hepatitis, haemorrhage etc).
    • Secondary superinfection is also more severe and dangerous


  • Usually not required, but investigations of complications (e.g. CXR, MRI) may be required


  • Again, most cases are self-limiting and won’t require any management other than anti-pyrexials and support, and can be managed at home.
  • Immunocompromised individuals, and anyone who develops a severe complication of chicken pox, should be admitted for treatment with IV aciclovir
  • Oral aciclovir may be given to patients with more severe disease requiring hospitalisation
    • Pregnant patients who have been in contact with someone with chicken pox should also be given oral treatment

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