INFLUENZA VIRUS INFECTIONS IN PREGNANT MICE

Abstract

The pregnancy rate of mice infected intranasally with PR8 influenza A virus (0.7 and 1.0 LD₅₀) was significantly reduced, but litter sizes were unaffected. Immune animals challenged with large doses were similar to controls in all respects. Intraperitoneal and intravenous routes of inoculation failed to reduce pregnancy rates or litter sizes. Influenza virus crossed the placenta late in the gestational period as evidenced by recovery of virus from fetuses. However, the possibility of virus recovery in newborn pups is unlikely, and maze studies tend to confirm the failure of the influenza virus to cross the placental barrier when pregnant mice are infected early in pregnancy.