Measles

Definition

Measles is an acute viral infection caused by the measles virus, characterized by fever, cough, coryza, conjunctivitis, and a characteristic maculopapular rash. It is highly contagious and can cause serious complications in children.

Epidemiology

• Peak incidence in children under 5 years in areas with low vaccination coverage
• Highly contagious with a basic reproduction number (R0) of 12–18
• Outbreaks more common in unvaccinated populations
• Globally, measles remains a leading cause of vaccine-preventable childhood morbidity and mortality
• Seasonal variation: often higher in late winter and spring

Etiology

• Measles virus, a single-stranded RNA virus of the Paramyxoviridae family
• Transmission via respiratory droplets, close contact, or airborne particles
• Secondary infection due to immunosuppression caused by the virus

Pathophysiology

• Virus infects respiratory epithelial cells, then spreads via lymphatics and bloodstream
• Replication in lymphoid tissues leads to viremia and systemic symptoms
• Immune response causes fever, rash, and lymphadenopathy
• Transient immunosuppression increases susceptibility to secondary bacterial infections
• Viral clearance typically occurs within 2–3 weeks in immunocompetent children