Pathology of Experimental Rocky Mountain Spotted Fever in Rhesus Monkeys

Abstract

Rhesus monkeys were inoculated intravenously or intraperitoneally with various numbers of Rickettsia rickettsii. Monkeys that were given more than 10⁴ organisms intravenously died on days 3–6 after inoculation, whereas those given less than 10³ intravenously or more than 10⁴ intraperitoneally died on day 7 or later. There was no significant difference in incidence of lesions between the early- and late-death groups. Vasculitis and thrombosis occurred most frequently in the nares, pinna of the ear, scrotal skin, and testicle. Adrenal cortical necrosis was caused by capillary thrombosis. Rickettsiae, estimated by plaque formation in culture, were most numerous in the lung and spleen.