Cytological investigation of Rickettsia tsutsugamushi infection of mice with different allotypic susceptibility to the agent.

Cytological and cytochemical studies on Swiss and random-bred white mice susceptible to Rickettsia tsutsugamushi infection as well as resistant C57 Black 6 and CBA mice revealed a clear-cut relationship between the severity of infection and the pattern of macrophage reaction. In highly susceptible mice the fatal infection was accompanied by death of macrophages and necrotisation of the peritoneal exudate cells. The resistant mice showed no clinical signs but developed an intensive macrophage reaction, and the main mass of the inoculated rickettsiae died at the inoculation site, the macrophages remaining viable. Phagocytosis and digestion of rickettsiae were accompanied by markedly increased activities of hydrolytic and oxidizing-reducing enzymes.