Chickenpox

Chickenpox, medically known as varicella, is a highly contagious viral infection caused by the varicella-zoster virus (VZV), a member of the herpesvirus family. Although commonly considered a childhood illness, it can affect individuals of all ages. In most children, the disease is mild and self-limiting, but in adults, immunocompromised individuals, and pregnant women, chickenpox can lead to severe complications such as pneumonia, encephalitis, and congenital varicella syndrome.

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Etiology and Pathophysiology

• Causative agent: Varicella-zoster virus (VZV), a double-stranded DNA virus.

• Transmission: Primarily through respiratory droplets and direct contact with vesicular fluid. The virus can also spread via airborne transmission.

• Incubation period: 10–21 days (average 14 days).

• Infectious period: From 1–2 days before rash onset until all lesions have crusted (usually about 5–7 days after rash begins).

• Pathogenesis:

  • Initial replication occurs in the nasopharynx and regional lymph nodes.

  • Viremia follows, spreading the virus to the skin and mucous membranes, resulting in the characteristic vesicular rash.

  • Following primary infection, the virus becomes latent in cranial nerve and dorsal root ganglia. Reactivation later in life leads to herpes zoster (shingles).

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Clinical Presentation

General Symptoms

• Prodromal phase (1–2 days before rash):

  • Fever, malaise, anorexia, headache, and irritability (more common in adults).

• Rash:

  • Progresses in stages: macules → papules → vesicles (“dew drop on a rose petal”) → pustules → crusting.

  • Lesions appear in crops over 2–4 days, leading to the presence of lesions in various stages simultaneously.

  • Distribution is centripetal (starts on trunk and face, spreads to extremities).

• Pruritus: Intense itching is a hallmark feature.

Complications

• Children: Secondary bacterial infections (e.g., impetigo due to Staphylococcus aureus or Streptococcus pyogenes).

• Adults: Severe disease with risk of pneumonia, hepatitis, or encephalitis.

• Pregnancy: Risk of congenital varicella syndrome, neonatal varicella, and severe maternal disease.

• Immunocompromised patients: Disseminated infection, prolonged viral shedding, and increased morbidity.

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Diagnosis

• Clinical diagnosis: Based on typical rash morphology and distribution.

• Laboratory confirmation (rarely needed):

  • Polymerase chain reaction (PCR) for VZV DNA (most sensitive).

  • Direct fluorescent antibody (DFA) testing.

  • Serology: IgM (acute infection) and IgG (immunity).

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Management

Most cases are mild and require symptomatic treatment, but antiviral therapy is indicated in specific populations.

1. Symptomatic Treatment

• Antipyretics:

  • Paracetamol (acetaminophen) 500 mg–1 g orally every 4–6 hours as needed (maximum 4 g/day in adults).

  • Aspirin should be avoided in children due to the risk of Reye’s syndrome.

• Antihistamines (for itching):

  • Chlorphenamine 4 mg orally every 4–6 hours (maximum 24 mg/day in adults).

  • Diphenhydramine 25–50 mg orally every 6 hours (in adults).

• Topical agents:

  • Calamine lotion or colloidal oatmeal baths to relieve itching.

  • Avoid scratching to reduce risk of scarring and secondary bacterial infection.

2. Antiviral Therapy

Antivirals reduce symptom duration and complication risk when started within 24 hours of rash onset.

• Acyclovir (generic):

  • Adults: 800 mg orally 5 times daily for 5 days.

  • Children (>12 years): 20 mg/kg orally 4 times daily (maximum 800 mg per dose) for 5 days.

• Valacyclovir (generic):

  • Adults: 1 g orally every 8 hours for 5–7 days.

• Famciclovir (generic):

  • Adults: 250 mg orally every 8 hours for 5–7 days.

• Intravenous Acyclovir (for severe disease or immunocompromised):

  • 10 mg/kg IV every 8 hours for 7–10 days.

3. Management in Special Populations

• Pregnancy:

  • Oral acyclovir may be considered if infection is severe and within 24 hours of rash onset.

  • Varicella-zoster immune globulin (VZIG) indicated after exposure in non-immune pregnant women.

• Immunocompromised individuals:

  • Intravenous acyclovir is first-line therapy.

  • Hospitalization and supportive care often required.

• Neonates (perinatal infection):

  • IV acyclovir 10 mg/kg every 8 hours for 10 days.

  • VZIG may be administered if exposed.

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Prevention

1. Vaccination

• Varicella vaccine (live attenuated):

  • Administered subcutaneously.

  • Children: 2 doses (first at 12–15 months, second at 4–6 years).

  • Adults (without prior infection or immunity): 2 doses, 0.5 mL each, 4–8 weeks apart.

  • Highly effective in preventing chickenpox and reducing severity.

2. Post-Exposure Prophylaxis

• Varicella-zoster immune globulin (VZIG):

  • Given within 10 days of exposure for high-risk individuals (immunocompromised, pregnant women, neonates).

• Antiviral prophylaxis:

  • Acyclovir or valacyclovir may be considered in exposed, high-risk individuals.

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Prognosis

• In healthy children, chickenpox is usually mild and self-limiting, with full recovery within 1–2 weeks.

• In adults, the risk of severe complications such as varicella pneumonia and encephalitis is significantly higher.

• Following infection, lifelong immunity is typically acquired, though the virus remains dormant and may reactivate as shingles later in life.

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Key Points for Clinical Practice

• Chickenpox is highly contagious; isolation is necessary until lesions crust over.

• Antivirals are reserved for adults, immunocompromised patients, pregnant women, and severe cases.

• Vaccination remains the most effective preventive measure.

• Avoid aspirin in children due to Reye’s syndrome risk.

• Special care is needed for neonates and pregnant women due to increased risk of complications.