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Rocky Mountain Spotted Fever

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dorsal view of a male cayenne tick, Amblyomma cajennense
This photograph shows a dorsal view of a male cayenne tick, Amblyomma cajennense. This tick species is a known North, Central, and South American carrier of Rickettsia rickettsii bacteria, which causes Rocky Mountain spotted fever. Credit: CDC

Rocky Mountain spotted fever 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 Washington, Montana, California, Arizona, and New Mexico.

The following pages have more information about Rocky Mountain spotted fever.

Last Updated July 08, 2014

Last Reviewed July 08, 2014