Measles is an acute, highly contagious viral disease caused by the measles virus. It is characterized by fever, upper respiratory tract inflammation, Koplik's spots, and a maculopapular rash. The measles virus is spherical and contains RNA. It is transmitted via airborne droplets from the respiratory tract of infected patients. Complications can include respiratory infections, encephalitis, and gastrointestinal involvement. Diagnosis involves detecting measles virus or antibodies in samples from patients showing symptoms.