Different allotypic susceptibility of mice to Rickett-sia tsutsugamushi.

Some lines of mice and random-bred mice show different susceptibility to infection with Rickettsia tsutsugamushi, displayed mainly in the development of overt infection. The latter is most markedly manifested in random-bred and Swiss mice, causing high death rates and massive accumulation of rickettsiae in the peritoneum. Black mice respond to inoculation with asymptomatic infection with no microscopically detectable rickettsiae. The infection is accompanied in either case by immunological response and persistence of the agent in mice. One of the mechanisms of resistance to R. tsutsugamushi in some mouse lines is due to phagocytosis at the inoculation site of the main mass of rickettsiae by macrophages which digest the agent and retain their viability.