Smallpox and measles: historical aspects and clinical differentiation.

Smallpox and measles have ravaged native populations worldwide for centuries. Millions of people have succumbed to smallpox or measles or suffered from their effects. Clinicians wonder how their predecessors confused measles with smallpox. The difficulty was in differentiating smallpox and measles in their early phases, which had important public health implications. The prodromal rash of smallpox sometimes resembled measles. Clinicians through the ages learned to differentiate smallpox and measles in their early stages. Osler's careful clinical description of prodromal smallpox is a classic in infectious diseases. Koplik's appreciation of the diagnostic significance of the spots on the buccal mucosa was another advance in the early diagnosis of measles. The clinical features and effects of measles and smallpox on history are reviewed.