A patient with Rocky Mountain spotted fever, courtesy CDC, via Wikipedia
Rocky Mountain spotted fever is a deadly, fairly common tick-borne infection that is endemic throughout the Western Hemisphere. It's classic symptoms are the sudden development of fever and muscle pain followed quickly by the development of a rash.
With these classic symptoms and any possibility of a tick bite, treatment with doxycycline or another appropriate antibiotic should be immediately started as the disease can be deadly within the period when the test to confirm it could be performed. Although modern medical treatment has reduced the mortality rate from 30%, it is still deadly and kills dozens of people a year. There are about 800 reported cases in the United States every year.
Rocky Mountain spotted fever at NIH