Most cases of ehrlichiosis have occurred in the south central and southeastern United States. Infection with E chaffeensis usually causes a nonspecific illness 7 days after exposure. The most common clinical features are high fever with headache, but the patient may complain of malaise, myalgia, nausea, vomiting, and anorexia. The risk of pneumonia in ehrlichiosis varies with the age of the patient. Dermacentor variabilis in the eastern United States and D andersoni in the western United States are responsible for the transmission of this infection to humans.
Most infections occur in the southeastern and coastal Atlantic states.
Rocky Mountain spotted fever is classically manifested by the triad of fever, rash, and history of tick exposure. The usual onset of illness is 5 to 7 days after inoculation. Fever, malaise, frontal headache, myalgia, and vomiting are common. This vasculitis also affects the pulmonary vasculature. Hemodynamic monitoring is essential in critically ill patients with Rocky Mountain spotted fever and pulmonary edema because the vasculitis associated with this illness can also affect the blood vessels of the myocardium, resulting in poor pump function.