Lack of transplacental infection with scrub typhus organisms in laboratory mice

Female mice were inoculated with either a virulent or avirulent strain of Rickettsia tsutsugamushi before (1 month and 1 week) or after (approximately 10 days) impregnation. From each group, two pregnant mothers were killed on day 20 post-impregnation, and fetuses and placentas were examined for rickettsiae. Organisms were isolated from 80% of placentas but not from the fetuses. Immediately following parturition, litters from 50% of the infected mothers were exchanged with litters from uninfected mothers. In all cases, no scrub typhus rickettsiae were found in the litters examined on days 1, 7, and 30 postpartum, and no antibody was found in sera collected 1 and 2 months postpartum.