This disease is caused by Rickettsia rickettsii and is transmitted by a number of different ticks. Despite its geographical title, Rocky Mountain spotted fever is present in many locations throughout the United States and the entire Western Hemisphere. After infection by tick bite, there is an incubation period of 2–14 days. The abrupt onset of the disease includes severe headache, fever, chills, arthralgia, and myalgia. After 2–3 days of these constitutional symptoms, erythematous macules erupt on the wrists, hands, forearms, legs, and ankles, as seen in these figures. Lesions then spread to the palms and soles and the trunk. The macules originally blanch with pressure but soon become purpuric and even necrotic. The disease causes a severe vasculitis and complications include disseminated intravascular coagulation, hemorrhage into the gastrointestinal and urinary tracts, and cardiovascular collapse. The Weil-Felix test is positive, but the disease must be treated immediately upon clinical suspicion. The high fatality rate is markedly reduced by prompt antibiotic therapy.