Rocky Mountain Spotted Fever (RMSF)

Rickettsial infections are caused by a variety of bacteria, and are most often transmitted to humans by infected fleas, lice, mites, and ticks. Rickettsial infections include Rocky Mountain spotted fever, typhus fever group, anaplasmosis, and ehrlichiosis.

Rocky Mountain spotted fever (RMSF)

Rocky Mountain spotted fever (RMSF) belongs to the spotted fever rickettsial group of tickborne infections. RMSF disease is caused by the bacterium Rickettsia rickettsii, transmitted to humans by the bite of an infected American dog tick (Dermacentor variabilis) and other tick species. Onset of illness begins about one week after an infected tick bite.

Symptoms of illness include acute onset of fever, headache, malaise, myalgia, nausea, vomiting, and rash. Severe illness may involve neurologic symptoms. Clinical laboratory findings may include thrombocytopenia, lymphopenia, leucopenia, and elevated liver enzymes. Between 2014 and 2018, only 87 cases were reported in the state. The majority of these reported cases were acquired outside of Wisconsin.

Close up image of dog tick

An American dog tick, which can transmit RMSF.

Graph of total Rocky Mountain Spotted Fever cases 2009-2018

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Last Revised: September 12, 2019