Rocky Mountain spotted fever (RMSF) is a tickborne disease first recognized in 1896 in the Snake River Valley of Idaho. It was originally called “black measles” because of the look of its rash in the late stages of the illness, when the skin turns black. It was a dreaded, often fatal disease, affecting hundreds of people in Idaho. By the early 1900s, the disease could be found in western states as far north as Washington and Montana and as far south as California, Arizona, and New Mexico.
Understanding Rocky Mountain Spotted Fever