Coxsackievirus B infection in pregnant mice and transplacental infection of the fetus.

Direct instillation of coxsackievirus B1 into the gastrointestinal tracts of albino mice caused viremia in more than 85% of the animals within 1 day. In pregnant mice infected early in gestation (7 days), the geometric mean titer of virus in the blood was lower (P = 0.02) and the duration of viremia was shorter (P = 0.07) than in nonpregnant female mice, but infection of the heart, liver, and uterus did not differ on each of 5 days after infection. Although transplacental infection of the placenta or fetus or both occurred, the high spontaneous abortion rate (48%) obviated comparison of transplacental infection in these mice with mice infected later in gestation. Pregnant mice infected in the third trimester had significantly greater geometric mean titers of virus in the blood, heart, liver, and uterus, and infection persisted longer than in nonpregnant mice (P = 0.04). A very high geometric mean titer of virus was recovered from the uteri of these mice for 3 days after infection, whereas simultaneous geometric mean titers of virus in the placentas and fetuses were lower. In the majority of third trimester pregnant mice, virus was found in low titers in the fetuses at 2 and 3 days after maternal infection, and virus was not detected after day 3. We conclude that coxsackievirus B1 infection in late gestational pregnant mice is more severe than in mice at earlier gestational stages and in nonpregnant mice and that transplacental infection of the fetus occurs transiently during maternal infection. This model will prove useful in the study of perinatal enterovirus infection and in examination of the numerous factors that may influence outcome of infection of perinatally infected newborn infants.