Chickenpox in Adolescence

Chickenpox (varicella) is a primary infection caused by the varicella-zoster virus (VZV), a neurotropic alpha-herpesvirus. While classically considered a benign disease of childhood (ages 1–9 years), chickenpox presents unique challenges and significantly higher risks when it occurs in adolescents (defined roughly as ages 10–19). In this age group, the disease is typically more severe, with a higher burden of lesions, more prolonged systemic symptoms, and a markedly increased risk of serious complications such as pneumonia. Consequently, management strategies for adolescents differ from those for younger children, specifically regarding the routine use of antiviral therapy.

Epidemiology and Pathogenesis

• Causative Agent: Varicella-zoster virus (VZV) is a double-stranded DNA virus. Primary infection causes varicella (chickenpox), while reactivation of latent virus causes herpes zoster (shingles).
• Transmission: VZV is highly contagious, spreading via the respiratory route (aerosolized droplets from nasopharyngeal secretions) or direct contact with vesicular fluid from skin lesions. Patients are infectious from 24–48 hours before the rash appears until all lesions have crusted (usually 4–7 days after rash onset).
• Adolescent Susceptibility: In temperate climates, most individuals acquire immunity during childhood. However, in tropical and subtropical regions (including parts of India), the peak age of infection is often delayed, leading to a higher proportion of susceptible adolescents and adults. This epidemiological shift is significant because morbidity and mortality rates increase with age.
• Pathogenesis: Following inhalation, the virus replicates in the upper respiratory tract and regional lymph nodes (primary viremia). It then spreads to the reticuloendothelial system (liver/spleen), followed by a secondary viremia that disseminates the virus to the skin (causing the rash) and viscera. The incubation period is typically 10–21 days (average 14–16 days).

Clinical Manifestations

The clinical course in adolescents is generally more severe than in young children.

1. Prodrome

Unlike young children who often present with the rash, adolescents frequently experience a distinct prodromal phase lasting 24–48 hours before the exanthem appears.

• Symptoms: Fever (often 37.8°C–38.9°C, but can be up to 41°C), malaise, anorexia, headache, and occasionally mild abdominal pain.
• Duration: Systemic symptoms usually persist for 2–4 days after the onset of the rash.

2. Exanthem (Rash)

• Evolution: The rash begins as intensely pruritic erythematous macules that rapidly progress to papules and then to clear, fluid-filled vesicles ("dewdrop on a rose petal"). Within 24–48 hours, the vesicles become cloudy (pustular) and eventually umbilicate and crust over.
• Distribution: The rash is centripetal, appearing first on the scalp, face, or trunk, and then spreading to the extremities. Lesions may also involve mucous membranes (oropharynx, vagina, conjunctiva).
• "Cropping": A hallmark of varicella is the simultaneous presence of lesions in all stages of evolution (macules, papules, vesicles, and crusts) in the same anatomical area.
• Severity in Adolescents: Adolescents typically have a higher number of lesions (often >500) compared to younger children. New crops of lesions may continue to appear for more than 7 days, and the overall duration of the illness is prolonged.

Complications

The risk of complications and mortality is significantly higher in adolescents and adults compared to children aged 1–9 years.

1. Varicella Pneumonia

This is the most serious complication in otherwise healthy adolescents and adults.

• Incidence: It occurs more frequently in adults/adolescents than in young children. Smoking is a known risk factor.
• Clinical Features: Symptoms usually begin 1–6 days after the onset of the rash and include cough, dyspnea, tachypnea, fever, pleuritic chest pain, and occasionally hemoptysis.
• Pathology: It is a primary viral pneumonia. Chest radiography typically shows diffuse bilateral infiltrates or nodular densities.
• Prognosis: It can progress rapidly to respiratory failure and acute respiratory distress syndrome (ARDS). Hypoxia can be severe.

2. Secondary Bacterial Infections

Superinfection of skin lesions is the most common complication in all age groups.

• Pathogens: Staphylococcus aureus and Group A Streptococcus (GAS).
• Manifestations: Impetigo, cellulitis, subcutaneous abscesses, and lymphadenitis. Severe invasive infections like necrotizing fasciitis or "varicella gangrenosa" (often due to GAS) can occur. Bacterial sepsis is a potential consequence.

3. Neurological Complications

• Encephalitis: Occurs in approximately 1 per 50,000 cases. It manifests with altered sensorium, seizures, and nuchal rigidity. Morbidity is highest in patients older than 20 years and younger than 5 years.
• Cerebellar Ataxia: Characterized by gait disturbance, nystagmus, and slurred speech. It is generally self-limited with a good prognosis.
• Other: Transverse myelitis, Guillain-Barré syndrome, and aseptic meningitis.

4. Other Complications

• Hematologic: Mild thrombocytopenia with petechiae is relatively common. Rare complications include purpura fulminans (associated with protein C/S deficiency) and disseminated intravascular coagulation (DIC).
• Organ Involvement: Hepatitis (usually asymptomatic enzyme elevation), myocarditis, nephritis, arthritis, and orchitis.

Diagnosis

Diagnosis is primarily clinical, based on the characteristic rash (cropping, pleomorphism) and history of exposure. Laboratory confirmation may be required in atypical or severe cases.

• Polymerase Chain Reaction (PCR): The most sensitive method. Can detect VZV DNA in vesicular fluid, crusts, or scrapings from maculopapular lesions.
• Direct Fluorescence Assay (DFA): Specific and rapid but less sensitive than PCR. Uses cellular material from the base of a vesicle.
• Tzanck Smear: Shows multinucleated giant cells but does not distinguish between VZV and HSV. Low sensitivity; generally not recommended if specific tests are available.
• Serology: IgM is unreliable. A fourfold rise in IgG antibodies in paired sera can confirm diagnosis retrospectively.

Management

The management of chickenpox in adolescents differs from that in young children because the risk of moderate-to-severe disease warrants the routine use of antiviral therapy.

1. Antiviral Therapy

• Indication: Treatment is recommended for all unvaccinated adolescents (typically defined as >12 or >13 years of age) because they are at increased risk for severe disease.
• Timing: To be effective, therapy must be initiated as early as possible, ideally within 24 hours of exanthem onset. Treatment started after 72 hours typically offers little clinical benefit unless new lesions are still appearing or complications are present.
• Drug of Choice: Acyclovir or Valacyclovir.
  • Oral Acyclovir: The standard dose is 800 mg orally, 5 times per day for 5–7 days. Alternatively, 20 mg/kg/dose (max 800 mg) 4 times daily.
  • Oral Valacyclovir: Valacyclovir has better oral bioavailability and a more convenient dosing schedule. The dose is 1,000 mg orally, 3 times daily for 5 days.
• Intravenous Acyclovir: Indicated for severe complications (e.g., pneumonia, encephalitis) or extensive disseminated disease in immunocompromised adolescents. The dose is 10 mg/kg (or 500 mg/m²) IV every 8 hours for 7–10 days.

2. Symptomatic and Supportive Care

• Antipyretics: Paracetamol (acetaminophen) is used for fever control. Aspirin (salicylates) must be strictly avoided due to the association with Reye syndrome. Ibuprofen is generally avoided due to a theoretical risk of increasing susceptibility to severe streptococcal skin infections (necrotizing fasciitis).
• Hygiene: Daily bathing and keeping fingernails short to prevent secondary bacterial infection from scratching.
• Antipruritics: Oral antihistamines (e.g., diphenhydramine, chlorpheniramine, cetirizine) and soothing lotions (e.g., calamine) to manage pruritus.
• Hydration: Essential, especially if there are oral lesions causing dysphagia.

3. Isolation

Adolescents with chickenpox should be excluded from school and public places until all lesions have crusted (usually 5–7 days) or, if no vesicles formed, until no new lesions have appeared for 24 hours.

Prevention

1. Vaccination

Varicella is a vaccine-preventable disease.

• Routine: Two doses of live-attenuated varicella vaccine are recommended.
• Catch-up: Adolescents with no history of varicella disease or vaccination should receive two doses of the vaccine. For persons aged ≥13 years, the two doses should be separated by 4–8 weeks.

2. Post-Exposure Prophylaxis (PEP)

If a susceptible adolescent is exposed to chickenpox:

• Vaccine: Administration of the varicella vaccine within 3 to 5 days of exposure is effective in preventing or modifying the severity of the disease (70–90% effective). This is the preferred method for immunocompetent adolescents.
• Varicella-Zoster Immune Globulin (VariZIG): Generally reserved for high-risk individuals (immunocompromised, pregnant women, newborns) who cannot receive the live vaccine. It should be given as soon as possible, ideally within 96 hours (up to 10 days) of exposure.
• Oral Acyclovir/Valacyclovir: Prophylaxis with antivirals starting late in the incubation period (e.g., day 7 after exposure) may modify disease but is not universally recommended as a standard public health measure compared to vaccination.

Prognosis

With timely diagnosis and appropriate antiviral therapy, the prognosis for adolescents with uncomplicated chickenpox is good. However, the mortality rate in unvaccinated adults and adolescents remains approximately 25 times higher than in children aged 1–4 years, primarily due to respiratory and CNS complications. Therefore, a high index of suspicion for complications and prompt initiation of acyclovir/valacyclovir are standard of care for this age group.