Varicella

Definition

Varicella, or chickenpox, is a highly contagious viral infection caused by the varicella-zoster virus (VZV), characterized by a vesicular rash, fever, and malaise. It primarily affects children but can occur in adults, where it tends to be more severe.

Epidemiology

• Worldwide distribution, most common in children under 10 years.
• Incidence has decreased in countries with routine varicella vaccination.
• Adults are at higher risk for severe disease and complications.
• Transmission occurs via respiratory droplets and direct contact with vesicular fluid.
• High attack rate among susceptible individuals (up to 90% in unvaccinated populations).

Etiology

• Varicella-zoster virus (VZV), a DNA herpesvirus.
• Primary infection causes varicella; reactivation later in life causes herpes zoster (shingles).
• Risk factors: unvaccinated status, immunocompromised individuals, pregnant women.

Pathophysiology

• Virus enters via respiratory tract and replicates in regional lymph nodes.
• Viremia leads to dissemination to skin and mucous membranes.
• Formation of characteristic vesicular lesions due to viral cytopathic effect and immune response.
• Cell-mediated immunity is crucial for viral clearance and lifelong immunity.
• Immunocompromised individuals have impaired viral clearance and higher risk of complications.