Chickenpox
A highly contagious viral infection causing an itchy, blister-like rash that appears in waves, typically affecting children.
Emergency Management: Varicella pneumonia or encephalitis requires immediate hospital admission for IV acyclovir and supportive care.
Chickenpox, or varicella, is a highly contagious systemic viral infection caused by the primary infection with the varicella-zoster virus (VZV). It is characterized by a generalized, pruritic, vesicular rash appearing in successive crops, accompanied by fever and systemic symptoms.
Detailed Overview
VZV is a human alphaherpesvirus. Infection occurs via respiratory droplets or direct contact with vesicular fluid. Following initial replication in the respiratory tract and regional lymph nodes, primary and secondary viremia lead to widespread cutaneous dissemination. Following primary infection, VZV establishes lifelong latency in the sensory dorsal root and cranial nerve ganglia, with potential to reactivate later as Herpes Zoster (shingles).
Epidemiology & Demographics
Before the introduction of the routine varicella vaccine in 1995, over 4 million cases occurred annually in the US. Since vaccination, incidence has declined by over 90%. It primarily affected children under 10 years old; however, unvaccinated adults are susceptible and prone to more severe disease. Peak incidence is in late winter and spring.
Etiological Mechanism
Varicella-Zoster Virus (VZV), a double-stranded DNA virus belonging to the Herpesviridae family (Human Herpesvirus 3).
Primary Causes
Transmission of VZV via inhalation of aerosolized respiratory droplets or direct contact with vesicular fluid from an infected individual.
VZV enters through the respiratory mucosa. It replicates in regional lymph nodes (days 2-4), causing a primary viremia (days 4-6). The virus then replicates in the reticuloendothelial system (liver, spleen), followed by a massive secondary viremia (days 10-14), disseminating to the skin and mucous membranes. In the epidermis, VZV infects keratinocytes, causing ballooning degeneration, intracellular edema, and formation of vesicles containing clear fluid filled with infectious virions. The immune response eventually clears the viremia, but the virus travels retrograde via sensory axons to establish latency in sensory ganglia.
Diagnostic Criteria & Guidelines
Diagnosis is primarily clinical, based on the characteristic history of exposure and the appearance of a generalized, pruritic, polymorphic vesicular rash. Laboratory confirmation is rarely necessary but can be done via PCR of vesicular fluid in atypical or severe cases.
For healthy children < 12 years: Supportive care only (Calamine lotion, oral antihistamines like Diphenhydramine 1.25 mg/kg Q6H PRN, and Acetaminophen for fever). AVOID aspirin due to Reye syndrome risk. For high-risk groups (>12 years, adults, immunocompromised, chronic cutaneous/pulmonary disorders): Oral Acyclovir (800 mg 5 times daily for 5-7 days in adults; 20 mg/kg QID for 5 days in children, max 800mg/dose) ideally initiated within 24 hours of rash onset.
Second-Line & Adjunctive Therapy
For severe or complicated varicella (e.g., pneumonia, encephalitis), or in immunocompromised patients: Intravenous Acyclovir (10 mg/kg IV every 8 hours for 7-10 days). Valacyclovir (1g PO TID for 5-7 days) is an alternative to oral acyclovir in immunocompetent adults.
Surgical & Procedural Management
Surgical debridement may be required for severe secondary bacterial infections like necrotizing fasciitis.
Patient Counseling & Advice
Advise parents to avoid administering aspirin or NSAIDs (ibuprofen may increase risk of severe skin infections, though data is mixed). Warn about signs of complications such as high prolonged fever, redness/swelling around spots, or difficulty breathing.
Follow-Up & Monitoring Schedule
Routine follow-up is not usually required for uncomplicated cases. Follow-up immediately if red flags appear.
Preventive Strategies
Routine childhood vaccination: Live attenuated varicella vaccine administered at 12-15 months and a second dose at 4-6 years. Post-exposure prophylaxis for susceptible high-risk individuals (e.g., immunocompromised, pregnant): Varicella-Zoster Immune Globulin (VariZIG) within 10 days (ideally 96 hours) of exposure.
Excellent in healthy children. Immunity is generally lifelong. Mortality is higher in normal adults (15x higher than children) and significantly higher in immunocompromised individuals.