Development of a classical swine fever subunit marker vaccine and companion diagnostic test

The development of a classical swine fever (CSF) subunit marker vaccine, ba sed on viral envelope glycoprotein E2, and a companion diagnostic test, bas ed on a second viral envelope glycoprotein E-RNS, Will be described. Import ant properties of the vaccine, such as onset and duration of immunity, and prevention of horizontal and vertical transmission of virus were evaluated. A single dose of the vaccine protected pigs against clinical signs of CSF, following intranasal challenge with 100LD(50) of virulent classical swine fever virus (CSFV) at 2 weeks after vaccination. However, challenge virus t ransmission to unvaccinated sentinels was not always completely inhibited a t this time point. From 3 weeks up to 6 months after vaccination, pigs were protected against clinical signs of CSF, and no longer transmitted challen ge virus to unvaccinated sentinels. In contrast, unvaccinated control pigs died within 2 weeks after challenge. We also evaluated transmission of chal lenge virus in a setup enabling determination of the reproduction ratio (R value) of the virus. In such an experiment, transmission of challenge virus is determined in a fully vaccinated population at different time points af ter vaccination. Pigs challenged at 1 week after immunization died of CSF, whereas the vaccinated sentinels became infected, seroconverted for E-RNS a ntibodies, but survived. At 2 weeks after vaccination, the challenged pigs seroconverted for E-RNS antibodies, but none of the vaccinated sentinels di d. Thus, at 1 week after vaccination, R>1, and at 2 weeks, R=0, implying no control or control of an outbreak, respectively. Vertical transmission of CSFV to the immune-incompetent fetus may lead to the birth of highly viraem ic, persistently infected piglets which are one of the major sources of vir us spread. Protection against transplacental transmission of CSFV in vaccin ated sows was, therefore, tested in once and twice vaccinated sows. Only on e out of nine once-vaccinated sows transmitted challenge virus to the fetus , whereas none of the nine twice-vaccinated sows did. Finally, our data sho w that the E-RNS test detects CSFV-specific antibodies in vaccinated or unv accinated pigs as early as 14 days after infection with a virulent CSF stra in. This indicates that the E2 vaccine and companion test fully comply with the marker vaccine concept. This concept implies the possibility of detect ing infected animals within a vaccinated population. (C) 2000 Elsevier Scie nce B.V. All rights reserved.