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Rocky Mountain Spotted Fever

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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 Washington, Montana, California, Arizona, and New Mexico.

In response to this health problem, the U.S. Public Health Service sent University of Chicago pathologist Dr. Howard T. Ricketts to the Bitterroot Valley of Montana, one of the disease hotspots. In 1906 Dr. Ricketts showed that the disease was transmitted by the bite of the Rocky Mountain wood tick. The work of Dr. Ricketts laid the foundation for what later became the Rocky Mountain Laboratories (RML) in Hamilton, Montana. Today, dozens of scientists continue to study tickborne and other diseases at RML, which is part of NIAID.

Though U.S. healthcare providers typically report about 250 to 1,200 cases of RMSF each year to the Centers for Disease Control and Prevention, a record 2,563 cases were reported in 2008.

RMSF is found throughout the United States from April through September. More than half of all cases occur in the mid-Atlantic to southern area of the United States (Delaware, Maryland, Washington, D.C., Virginia, West Virginia, North Carolina, South Carolina, Georgia, Oklahoma, and Florida). North Carolina, Missouri, and Oklahoma report the greatest number of people with RMSF. Although the disease was first discovered in the Rocky Mountains, the area has relatively few cases today.

The disease also has been found in Canada and in Central and South America.

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Last Updated January 28, 2011

Last Reviewed January 28, 2011