Japanese encephalitis virus infection in fetal mice at different stages of pregnancy I. Stillbirth.

The relationship between the stage of pregnancy at the time of Japanese encephalitis (JE) virus inoculation and the frequency of stillbirth was investigated in mice. Pregnant mice inoculated at nine to sixteen days before parturition demonstrated a higher frequency of stillbirth (38%, 12/32) than mice similarly inoculated at one to eight (20%, 6/30) or at seventeen to twenty (14%, 2/14) days respectively before parturition. Stillbirth frequency in the control group was 1.4% (1/72). Five out of thirteen stillborn of mothers inoculated at nine to sixteen days before parturition were positive in virus isolation tests, and three others showed congenital malformations, anencephaly, encephalocele and underdevelopment below the waist.