Early diagnosis of Rocky Mountain spotted fever. Use of primary monocyte culture technique.

Diagnosis of Rocky Mountain spotted fever was made as early as the fourth day of febrile illness in rhesus monkeys (Macaca mulatta), with a monocyte culture technique that is easily amenable to use in humans. Rickettsia rickettsii were identified by direct immunofluorescent and Gimenez staining of cultures of circulating monocytes from four experimentally infected monkeys, even in the presence of a mild or inapparent disease in three. Levels of rickettsemia were estimated by the plaque-assay technique, and specific antibody titers were determined by complement fixation.