Rickettsial organisms infect humans worldwide, although geographic locations may be limited for some species and possibly produce some challenges in medical diagnosis. All are obligate intracellular parasites, except C. burnetii, and transmitted by an insect vector. Typhus, spotted fever, and scrub typhus share which of the following manifestations of disease?

Typhus, spotted fever, and scrub typhus are all caused by rickettsiae (R. prowazekii, R. rickettsii, and R. tsutsugamushi, respectively). Clinically, the diseases have several similarities. Each has an incubation period of 1 to 2 weeks, followed by a febrile period, which usually includes a rash. During the febrile period, rickettsiae can be found in the patient's blood, and there is disseminated focal vasculitis of small blood vessels. The geographic area associated with these diseases is usually different. Scrub typhus is usually found in Japan, Southeast Asia, and the Pacific, while spotted fever is usually found in the western hemisphere. Typhus has a worldwide incidence. (Typhus is caused by lice and fleas, spotted fever is caused by ticks and mites, and scrubs are caused by mites.)