Innocuousness and safety of classical swine fever marker vaccine candidate CP7_E2alf in non-target and target species

Abstract

Chimeric pestivirus CP7_E2alf is a promising live marker vaccine candidate against classical swine fever. Prior to a possible application in the field, several safety aspects have to be addressed. Due to the fact that CP7_E2alf is based on a bovine viral diarrhea virus backbone, its behavior in ruminants is of particular interest. In the framework of this study, its innocuousness in non-target species was addressed by inoculation of calves, young goats, lambs, and rabbits. To this means, high titres of CP7_E2alf were applied orally to three animals of each species. Additional animals were left as unvaccinated contact controls. During the study, all animals remained clinically healthy, and neither fever nor leukopenia were observed. Virus could not be isolated from purified white blood cells or from nasal or faecal excretions. Moreover, none of the animals (inoculated or contact control) seroconverted. In the target species, innocuousness, shedding and transmission of vaccine virus was addressed in different animal trials that were carried out primarily for the purpose of efficacy, potency or duration of immunity studies. In all experiments, CP7_E2alf proved to be completely safe for the vaccinees and unvaccinated contact controls. Furthermore, no shedding or transmission was detected in any of the experiments. Even after parental vaccination, vaccine virus genome was barely detectable in blood or organ samples of vaccinated animals. Thus, CP7_E2alf can be regarded as completely safe for both target and non-target species.