Chickenpox

Last Updated on by frcemuser

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. 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

  • Varicella is very infectious; up to 90% of susceptible contacts develop the disease.
  • Transmission is by personal contact or droplet spread, with an incubation period of 1–3 weeks.
  • Chickenpox is infectious from 1–2 days before the rash appears until the vesicles are dry or have crusted over, usually 5 days after the onset of the rash (this period may be longer in people who are immunocompromised).
  • Once the infection has subsided, the virus persists in sensory nerve root ganglia. Years or decades later, it can reactivate and cause herpes zoster (shingles)
  • It is possible to develop chickenpox after exposure to a person with shingles, but it is not possible to develop shingles from exposure to a person with 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.

Clinical features include:

  • A prodrome that includes nausea, myalgia, anorexia, and headache (particularly adolescents and adults)
  • General malaise, loss of appetite, and feeding problems
  • Fever
  • Characteristic rash
    • Small, erythematous macules appear on the scalp, face, trunk, and proximal limbs, which progress over 12–14 hours to papules, clear vesicles (which are intensely itchy), and pustules.
    • Vesicles can also occur on the palms and soles, and mucous membranes can also be affected, with painful and shallow oral or genital ulcers.
    • Vesicles appear in crops; stages of development of the rash can therefore differ on different areas of the body.
    • Crusting occurs usually within 5 days of the onset of the rash, and crusts fall off after 1–2 weeks.

Differential diagnosis

  • Other vesicular viral rashes, such as:
    • Herpes simplex (not usually disseminated)
    • Herpes zoster (usually unilateral and localised to dermatomes)
    • Hand, foot, and mouth disease (caused by Coxsackie virus)
  • Other infections, such as:
    • Impetigo
    • Scabies
    • Syphilis
    • Meningococcaemia (can be confused with haemorrhagic varicella)
    • Toxic shock syndrome
  • Skin disorders, such as:
    • Guttate psoriasis
    • Drug eruption
    • Insect bites
    • Papular urticaria
    • Erythema multiforme
    • Stevens–Johnson syndrome
    • Henoch–Schönlein purpura
    • Dermatitis herpetiformis

Management

  • If serious complications (such as pneumonia, encephalitis, or dehydration) are suspected, admit to hospital.
  • Antiviral treatment:
    • Consider prescribing oral aciclovir 800 mg 5 times a day for 7 days for an immunocompetent adult or adolescent (aged 14 years or older) with chickenpox who presents within 24 hours of rash onset, particularly for people with severe chickenpox or those at increased risk of complications, such as smokers.
    • Aciclovir is not recommended for otherwise healthy children with chickenpox.
  • Symptomatic treatment:
    • Paracetamol if pain or fever are causing distress (avoid nonsteroidal anti-inflammatory drugs)
    • Topical calamine lotion to alleviate itch
    • Chlorphenamine for treating itch associated with chickenpox for people 1 year of age or older
  • Patient advice:
    • Advise that the most infectious period is 1–2 days before the rash appears, but infectivity continues until all the lesions are dry and have crusted over (usually about 5 days after the onset of the rash).
    • During this time, advise a person with chickenpox to avoid contact with:
      • People who are immunocompromised
      • Pregnant women
      • Infants aged 4 weeks or less
    • Advise that children with chickenpox should be kept away from school or nursery until all the vesicles have crusted over.

Complications

  • Complications in children
    • Chickenpox is usually a self-limiting disease in healthy children, and complications are rare. However, complications may occur, including:
      • Skin bacterial superinfection (for example impetigo, furuncles, cellulitis, erysipelas, necrotising fasciitis) and scarring
      • Neurological complications (for example Reye’s syndrome, acute cerebellar ataxia, encephalitis, meningoencephalitis, polyradiculitis, myelitis)
      • In rare cases, myocarditis, glomerulonephritis, appendicitis, pancreatitis, Henoch–Schönlein purpura, orchitis, arthritis, optic neuritis, iritis, and keratitis
  • Complications in adults
    • Chickenpox can be more serious in adults than in children, and adults with varicella are more likely to be admitted to hospital. Complications include pneumonia, hepatitis, and encephalitis. Shingles can occur from reactivation of latent varicella-zoster infection.
  • Complications in pregnancy
    • Varicella in pregnancy can result in severe chickenpox. The mother is at increased risk of varicella pneumonia and other complications, compared with the general adult population.
    • Infection with varicella-zoster during the first 28 weeks of pregnancy can lead to intrauterine infection and fetal varicella syndrome, which is characterised by one or more of:
      • Skin scarring in a dermatomal distribution
      • Eye defects (for example microphthalmia, chorioretinitis, and cataracts)
      • Hypoplasia of the limbs
      • Neurological abnormalities (microcephaly, cortical atrophy, learning difficulties, dysfunction of bowel and bladder sphincters)
  • Complications in neonates
    • Neonates are at increased risk of disseminated or haemorrhagic varicella. If the mother becomes infected 1–4 weeks before delivery, up to half of babies will be infected; and around a quarter will develop clinical varicella of the newborn, even though they have passively acquired maternal antibody.

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