An experimental infection with classical swine fever in E2 subunit marker-vaccine vaccinated and in non-vaccinated pigs

The clinical and virological protection induced by an E2 sub-unit marker-vaccine against Classical Swine Fever (CSF) was examined during an experimental infection in vaccinated and non-vaccinated pigs. Forty-five pigs were equally distributed over three adjacent pens of an isolation unit, there was only indirect (airborne) contact between pigs in the different pens. In pen 3 all pigs were vaccinated twice with 4 weeks interval. Pigs in pens 1 and 2 were not vaccinated. Two weeks after booster vaccination, one randomly selected pig in the middle pen was experimentally inoculated with CSF virus. After the initial virus spread in the infected pen, all pigs in the non-vaccinated adjacent pen were infected. In the vaccinated pen, seven out of 14 pigs became infected during the experiment. Survival analysis showed that virus transmission by direct and indirect contact was significantly (p < 0.001) delayed in vaccinated pigs as compared to non-vaccinated pigs. In the non-vaccinated pens over 40% of the pigs died and typical clinical signs were noticed. In the vaccinated pen no mortality and no clinical symptoms were observed. Although double vaccination with an E2 sub-unit marker-vaccine was able to prevent the clinical course of the disease it was unable to prevent infection through indirect contact. This finding combined with the slow serological response after vaccination will complicate the possible use of the vaccine in emergency vaccination programmes. (C) 2000 Elsevier Science Ltd. All rights reserved.