Microbiology

Rickettsiae are obligate intracellular gram-negative coccobacilli and short bacilli usually transmitted by tick, mite, flea, or louse vectors. Except in the case of louse-borne typhus, humans are incidental hosts.

Clinical Manifestations

The clinical manifestations of all the acute rickettsial presentations are similar during the first 5 days and consist of nonspecific signs and symptoms: fever, headache, and myalgias with or without nausea, vomiting, and cough. As the course progresses, clinical manifestations-including occurrence of a macular, maculopapular, or vesicular rash; eschar; pneumonitis; and meningoencephalitis-vary from one disease to another. (See Table 99-1 Features of Selected Rickettsial Infections and details below.)