Oral vaccination against classical swine fever with a chimeric Pestivirus: comparative investigations of liquid and lyophilized virus

The goal of this study was to evaluate the efficacy of the chimeric marker vaccine candidate CP7_E2alf in different formulations for oral immunization against classical swine fever (CSF). In the first experiment, three wild boars were vaccinated orally with the liquid chimeric virus CP7_E2alf, whereas in the second experiment, four wild boars and four domestic pigs were immunized with the lyophilized chimera administered in gelatine capsules and new baits. The chimera was safe for wild boars and domestic pigs. All animals vaccinated orally with the liquid chimera were seropositive 21 days after vaccination, and neither viraemia nor virus shedding were observed after challenge with a highly virulent CSF virus. At necropsy, viral genome of the challenge virus was detected in some organs of all surviving wild boars. Lyophilized chimera administered orally did not protect the animals. The reasons for the inefficacy of the lyophilized vaccine virus are discussed. Irrespective of the negative result with lyophilized virus, the study and previous experiences (Reimann et al., Virology, 307:213-227, 2004) suggest that the chimera CP7_E2alf is a potential CSF marker vaccine candidate