Failure to Induce Fetal Infection by Inoculation of Pregnant Immune Heifers with Bovine Parainfluenza 3 Virus

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Abstract
Ten pregnant heifers with serum neutralizing (SN) antibody to parainfluenza 3 virus were inoculated at midgestation with an isolate of bovine parainfluenza 3 (PI-3) virus recovered from an aborted bovine fetus. Eight of the heifers delivered healthy full-term calves with precolostral titers of SN antibody to PI-3 that were < 1:4 dilution. Two calves were dead at birth; virus was not isolated from the tissues, and they had no detectable precolostral antibody to PI-3 virus. All heifers responded immunologically, and the antibody formed apparently neutralized the inoculum of PI-3 virus, thereby avoiding transplacental infection. The fetuses of two heifers were inoculated in utero with the PI-3 fetal isolate as a positive control. The two calves were delivered alive within the normal duration of pregnancy, but were weak and unable to rise. One calf died 30 hr after birth, the second was killed 6 hr after birth. Both calves had elevated precolostral titers of SN antibody to PI-3 virus.

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