Rocky Mountain spotted fever (RMSF) is the most severe tick-borne illness in the United States. Most people who get RMSF will have a fever, headache, and rash. RMSF is treated with antibiotics; however, if treatment is delayed RMSF can be deadly. RMSF is transmitted through the bite of an American dog tick, Rocky Mountain wood tick, or brown dog tick. There is no vaccine to prevent RMSF. The best way to prevent infection is to prevent tick bites, prevent ticks on your pets, and prevent ticks in your yard.