This document discusses measles, an acute viral infection characterized by a maculopapular rash. It covers the etiology (measles virus), epidemiology (endemic worldwide, high transmission rate), clinical features (incubation 10-12 days, prodrome of fever and cough, pathognomonic Koplik's spots, spreading rash), diagnosis (clinical features, IgM antibodies, virus isolation), and differentiation from other rash-causing illnesses. Measles is highly contagious and can cause severe illness or death, especially in malnourished or unvaccinated children.