The Persian physician Muhammad ibn Zakariya al-Rhazes (865 - 925 AD) was the first to describe measles as different than smallpox. His work was translated many times and was still being used 800 years later. His observations and treatments for measles were included in this 1748 book by Richard Mead. Dr. Richard Mead (1673 - 1754 ) was a fellow of the Royal Colleges of Physicians in London and Edinburgh. The British government asked him to write about smallpox and measles because the idea of disease spreading through the air from one infected person to another was new and not well understood. 

The symptoms of measles are very similar to those of smallpox and for centuries the diseases were synonymns in Western medicine. Thomas Sydenham (1624 -1689) was an English physician who made detailed examinations about his patients and based his treatments on what he learned from his observations. He published a general medical book in 1666 and the fourth section addressed smallpox. He urged physicians not to hasten or slow down the course of the disease by administering hot cordial drinks, vomits or other purges, or bloodletting. Over the next 10 years he continued to make detailed observations about patients and published a second edition of his book in 1676. In this edition, Sydenham differentiates smallpox from measles although the treatments are very similar. His second book became a standard medical textbook for the next 200 years.