rocky Mountain spotted fever (rMSF), an acute febrile (feverish) disease initially recognised 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. 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. Also called spotted fever and tick fever.