Transmission of Aujeszky's disease (pseudorabies) virus is blocked by trypsin treatment of transferred embryos

Four seronegative sows from a farm free of Aujeszky's disease (AD) were artificially inseminated and concurrently infected intranasally and intrauterinally with 105 dose of a virulent strain of Aujeszky's disease virus (ADV). The embryos were recovered surgically 5 d later. The virus could be re-isolated from nasal and vaginal swabs and from different parts of the genital organs (ovary, oviduct, uterus and cervix) of all infected sows. In 2 of the infected sows ADV was also found in the flushing medium used for embryo recovery. The results of virus isolation were confirmed by dot-blot hybridization and histological findings. Embryos with an intact zona pellucida (ZP) collected from the 4 donors were treated twice with 0.25% trypsin solution for 1 min each time prior to transfer into a seronegative sow. The recipient sow and her offspring remained ADV-seronegative on Day 28 after farrowing, indicating that the transmission of ADV had been blocked during the embryo transfer. Untreated control embryos transferred into AD-free recipients caused seroconversion based on the serum neutralization test carried out 40 d later.