Dose‐Dependent Transplacental Infection of Murine Encephalomyelitis Virus GDVII in Gravid Uterus

Intrauterine infection of murine encephalomyelitis virus GDVII was investigated by the indirect immunofluorescence method. Sixty-day-old pregnant mice were inoculated with 5 gradated doses of the virus ranging from 0.001 to 1.5 MLD50 via i.v. route on the 10th day of gestation. The mice exsanguinated on postinfection day 8 showed high incidences of viral antigen in the uterine walls, placentas, and fetal subcutaneous tissues with doses of 0.1-1.5 MLD50, regardless of the presence of maternal symptoms. Incidence of viral antigen-positive cells in fetal brains was high with a dose of 0.1 MLD50, but not by the other doses. However, the brains of the stillborn and newly-born mice derived from females infected by a dose of 0.5 MLD50 brought about still higher detection rates of viral antigen, as well as in the postpartum uteri. In effect, transplacental transmission of the virus was clearly demonstrated, and appeared to be dose-dependent.