Prevention of transplacental transmission of moderate-virulent classical swine fever virus after single or double vaccination with an E-2 subunit vaccine

The use of a vaccine against classical swine fever virus (CSFV) during an o utbreak of CSF should lead to a reduction in the horizontal or vertical tra nsmission of CSFV, The reduction of vertical, i.e. transplacental, transmis sion of a moderate-virulent strain of CSFV from the sow to its offspring wa s 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 subuni t vaccine, approximately four weeks before insemination. A third group of n ine inseminated sows served as controls. One group of nine sows were vaccin ated again at two weeks after insemination, At ten weeks after the primary vaccination, approximately six weeks after insemination, all 27 sows were c hallenged intranasally with 10(5) TCID50 of a moderate-virulent strain of C SFV, the Van Zoelen strain. The sows were euthanized at five weeks after ch allenge, 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 i n the fetuses of all unvaccinated sows but it was not detected in any of th e samples collected from fetuses of the double-vaccinated sows. Virus was h owever recovered from the fetuses of one out of nine sows vaccinated once. All the sows, except four double-vaccinated sows, developed CSFV E-rns anti bodies. Transplacental transmission of CSFV was reduced significantly (p < 0.001) in all vaccinated sows. When the results from the experiment were ex trapolated to a herd level, it could be concluded that, with 95% certainty, approximately 11% (single vaccination) or 0% (double vaccination), confide nce intervals of 0.01-0.44 and 0.0-0.30 respectively, of the pregnant sows would still not be protected against vertical transmission of moderate-viru lent CSFV. We conclude that vaccination with the CSFV E-2 subunit vaccine can reduce t he transmission of moderate-virulent strain of CSFV from the sow to its off spring significantly.