A rickettsial disease often characterized by a primary “punched out” skin ulcer (eschar) corresponding to the site of attachment of an infected mite. An acute febrile onset follows within several days, along with headache, profuse sweating, conjunctival injection and lymphadenopathy. Late in the first week of fever, a dull red maculopapular eruption appears on the trunk, extends to the extremities, and disappears in a few days. Cough and X-ray evidence of pneumonitis are common. Without antibiotherapy, fever lasts for about 14 days. The case-fatality rate in untreated cases varies from 1% to 60%, according to area, strain of infectious agent, and previous exposure to disease; it is consistently higher among older people.

Definitive diagnosis is made by isolation of the infectious agent by inoculating the patient's blood into mice. Serological diagnosis is complicated by antigenic differences of various strains of the causal rickettsia; the IF test is the preferred technique, but EIAs are also available. Many cases develop a positive Weil-Felix reaction with the Proteus OXK strain.