Definition of Fever, Rocky Mountain spotted (RMSF)

Fever, Rocky Mountain spotted (RMSF): An acute febrile (feverish) disease initially recognized in the Rocky Mountain states, caused by Rickettsia rickettsii transmitted by hard-shelled (ixodid) ticks. Occurs only in the Western Hemisphere. Anyone frequenting tick-infested areas is at risk for RMSF.

The onset of symptoms is abrupt with headache, high fever, chills, muscle pain. and then a rash. The rickettsiae grow within damaged cells lining blood vessels which may become blocked by clots. Blood vessel inflammation (vasculitis) is widespread.

Early recognition of RMSF and prompt antibiotic treatment is important in reducing mortality.

The first person to describe the disease was an ear, nose and throat specialist, Edward Ernest Maxey. Maxey reported the disease in 1899. Seven years later, a pathologist named Howard Taylor Ricketts showed that it was transmitted by a tick bite. The agent that causes the disease was named for him -- Rickettsia rickettsii.

Rocky Mountain spotted fever is also called spotted fever, tick fever, and tick typhus.