Varicella (chicken pox)

B01

DESCRIPTION

An acute, highly contagious, viral disease caused by herpes varicella-zoster. It spreads by infective droplets or fluid from vesicles. One attack confers permanent immunity. Varicella is contagious from about 2 days before the onset of the rash until all lesions crusted.

Re-activation of the virus may appear later as herpes zoster or shingles (in children, consider immunosuppression if this occurs).
Incubation period is 2–3 weeks.

Complications are more common in immunocompromised patients and include:

  • secondary skin infection,
  • pneumonia,
  • necrotising fasciitis,
  • encephalitis,
  • haemorrhagic varicella lesions with evidence of disseminated, intravascular coagulation.
  • Two important bacteria causing complications are Staphylococcus aureus and Streptococcus pyogenes .

DIAGNOSTIC CRITERIA

Clinical

  • Mild headache, fever and malaise.
  • Characteristic rash.
  • The lesions progress from macules to vesicles in 24–48 hours.
  • Successive crops appear every few days.
  • The vesicles, each on an erythematous base, are superficial, tense ‘teardrops’ filled with clear fluid that dries to form fine crusts.
  • The rash is more profuse on the trunk and sparse at the periphery of extremities.
  • At the height of eruption, all stages (macules, papules, vesicles and crusts) are present at the same time.
  • The rash lasts 8–10 days and heals without scarring, unless secondarily infected.
  • Mucous membranes may be involved.
  • Pruritus may be severe.
  • Patients are contagious from 1–2 days before onset of the rash until crusting of lesions.

GENERAL AND SUPPORTIVE MEASURES

  • Isolate the patient.
  • Maintain adequate hydration.

MEDICINE TREATMENT

Antiviral therapy

Indicated for immunocompetent patients with complicated varicella and for all immunocompromised patients.
Initiate as early as possible, preferably within 24 hours of the appearance of the rash.

Neonates, immunocompromised patients and all cases with severe chickenpox (not encephalitis)

  • Aciclovir, oral, 20 mg/kg/dose 6 hourly for 7 days.
    • Maximum dose: 800 mg/dose.

In severe cases or in cases where oral medicine cannot be given:

  • Aciclovir, IV, 8 hourly administered over 1 hour for 7 days
    • If 0 – 12 years: 20 mg/kg/dose 8 hourly.
    • If > 12 years: 10 mg/kg/dose 8 hourly.

For encephalitis:
See Meningo-encephalitis/encephalitis, acute viral .

For mild pruritus:

  • Calamine lotion, topical, applied 8 hourly.

For severe pruritus:

  • Less than 2 years: Chlorphenamine, oral, 0.1 mg/kg 6–8 hourly for 24–48 hours.
  • Over 2 years: Cetirizine, oral, 2.5-5 mg 12-24 hourly.

Secondary skin infection

  • Cephalexin, oral, 12.5 mg/kg/dose, 6 hourly for 5 days.

Prophylaxis

Post exposure prophylaxis must be given to:
Neonates whose mothers develop varicella from 5 days before delivery to 2 days after delivery:

  • Varicella-zoster immunoglobulin, IM, 1 mL (100 units) given within 96 hours of exposure.

If varicella-zoster immunoglobulin is not available:

  • Aciclovir, oral, 20 mg/kg/dose 6 hourly for 10 days.

Note:
In neonates, prophylaxis may not prevent disease.

Infants and children > 28 days

Immunocompromised children exposed to varicella:

  • Aciclovir, oral, 20 mg/kg/dose 8 hourly for 10 days given in the second week after exposure.

Hospitalised immunocompetent children exposed to varicella (to limit spread).

  • Varicella-zoster vaccine, IM, 0.5 mL given within 72 hours of exposure.
    OR
  • Aciclovir, oral, 20 mg/kg/dose 8 hourly for 10 days given in the second week after exposure.

REFERRAL

  • Patients with complications.