Embryonic death in pregnant rats owing to intercurrent infection with Sendai virus and Pasteurella pneumotropica

During an outbreak of Sendai virus infection in a colony of rats used for embryo production, severe lung lesions due to secondary colonization of the rat lungs with Pasteurella pneumotropica were noted. The effect on pregnancy was to cause embryonic death and resorption, leaving a deciduoma with trophoblastic giant cells as the only embryonic remnants. Up to 30% of fetuses in each pregnant animal were affected at the time of severe maternal lung lesions. Heavy growths of Pasteurella pneumotropica were obtained from the lungs of all affected dams. The formation of deciduomas as a result of embryonic death was due to the indirect effect of damage to the lungs during pregnancy rather than the direct pathogenic effect on the developing embryo of the microbial organisms isolated.