Influenza A virus and its influence on the outcome of pregnancy in the mouse.

The effect of sub-lethal doses of influenza A strains WSN (H0N1), MEL (H0N1) and MRC-7 (H3N2) administered intranasally during pregnancy was studied in C3H inbred and Prince Henry outbred mice. Maternal and neonatal mortality rates were significantly increased by infections in the last third of the gestational period. Infection with influenza strain WSN in the last part of the first third of the gestational period significantly depressed the growth rate of neonates. No evidence of viraemia, transplacental transmission or congenital malformations were observed. Invasion of alveolar spaces by mononuclear phagocytes and erythrocytes was more pronounced in pregnant mice infected in the last third of the gestational period than in non-pregnant mice, and paralleled an ablation of cell-mediated immune responsiveness.