Prevention of transplacental transmission of moderatevirulent classical swine fever virus after single or double vaccination with an e2subunit vaccine

Abstract

The use of a vaccine against classical swine fever virus (CSFV) during an outbreak of CSF should lead to a reduction in the horizontal or vertical transmission of CSFV. The reduction of vertical, i.e. transplacental, transmission of a moderate‐virulent strain of CSFV from the sow to its offspring was studied in sows vaccinated once or twice with a CSFV E₂ subunit vaccine. Two groups of nine sows were vaccinated with one PD₉₅ dose of the E₂ subunit vaccine, approximately four weeks before insemination. A third group of nine inseminated sows served as controls. One group of nine sows were vaccinated again at two weeks after insemination. At ten weeks after the primary vaccination, approximately six weeks after insemination, all 27 sows were challenged intranasally with 10⁵ TCID₅₀ of a moderate‐virulent strain of CSFV, the Van Zoelen strain. The sows were euthanized at five weeks after challenge, and samples from the sows and fetuses were collected for detection of CSFV. All 27 sows were in gestation at the time of slaughter, CSFV was detected in the fetuses of all unvaccinated sows but it was not detected in any of the samples collected from fetuses of the double‐vaccinated sows. Virus was however recovered from the fetuses of one out of nine sows vaccinated once. All the sows, except four double‐vaccinated sows, developed CSFV E^rns antibodies. Transplacental transmission of CSFV was reduced significantly (p 2 subunit vaccine can reduce the transmission of moderate‐virulent strain of CSFV from the sow to its offspring significantly.