Define Chickenpox. Describe its clinical features, complications and management.

Definition

• Chickenpox is a highly contagious primary infection with the varicella-zoster virus (VZV), spread by respiratory droplets and direct contact.
• The virus becomes latent in dorsal-root ganglia and can later reactivate as herpes zoster (shingles).

Clinical Features

• Mild fever and malaise, followed by an intensely itchy vesicular rash.
• Rash is centripetal (trunk more than limbs), begins as macules → papules → vesicles ('dew drop on a rose petal') → crusts.
• Pleomorphism — lesions in different stages simultaneously (a key distinguishing feature).

Complications

• Secondary bacterial infection of skin lesions (commonest).
• Pneumonia (especially adolescents/adults), cerebellar ataxia and encephalitis.
• Congenital varicella syndrome (early-pregnancy maternal infection) and severe neonatal varicella.

Management & Prevention

• Supportive — antipyretics (not aspirin — Reye syndrome risk), antihistamines and skin care.
• Aciclovir for high-risk groups — immunocompromised, neonates, adolescents/adults, and severe disease.
• Post-exposure — VZIG for susceptible high-risk contacts; varicella vaccine for prevention.

Incubation & Infectivity

• Incubation ~14–16 days; infectious from ~1–2 days before the rash until all lesions crust.
• Susceptible contacts (household) are at high risk — hence isolation.

Herpes Zoster (reactivation)

After primary chickenpox, VZV stays latent in the dorsal-root ganglia and can reactivate years later as herpes zoster (shingles) — a painful dermatomal vesicular rash — particularly with waning immunity or immunosuppression.

A Note on WHY the Rash Is in 'crops'

• A useful and highly diagnostic observation is understanding why the rash of chickenpox shows lesions at different stages of evolution at the same time — and why this single feature distinguishes it from smallpox.
• In varicella, the virus is released into the blood in successive waves of viraemia over several days — so new crops of lesions keep appearing while the earlier ones are already maturing.
• The result is that at any moment one sees macules, papules, vesicles ('a dew-drop on a rose petal'), pustules and crusts all together in the same area of skin — the classic 'pleomorphism'.
• In smallpox, by contrast, the lesions all appeared simultaneously and evolved together, in lock-step — and they were centrifugal (dense on the face and limbs) rather than centripetal (dense on the trunk, as in chickenpox).
• Two further practical points.
• The child is infectious from 1–2 days before the rash until all the lesions have crusted.
• And aspirin must never be given — it precipitates REYE'S syndrome (acute encephalopathy with fatty liver).
• Chickenpox is far more severe in adolescents, adults, the immunosuppressed, and the newborn.