The present invention relates to chimeric pestiviruses having utility as immunogenic compositions and vaccines. Also described herein are methods and kits for treating or preventing the spread of bovine viral diarrhea virus infection, as well as methods and kits for differentiating between vaccinated and wild-type infected animals.

The role of a specific E2 region, .sup.869CKWGGNWTCV.sup.878, containing a putative fusion peptide (FP) sequence was evaluated. FPs critically contribute to the interaction between proteins and the membrane system of the host cell. Reverse genetics utilizing a full-length infectious clone of the highly virulent CSFV strain Brescia (BICv) was used to evaluate how amino acid substitutions within this region of E2 may affect replication of BICv in cell cultures and affect virus virulence in swine. A recombinant CSFV (FPi.c) containing mutations in three amino acid residues within the E2 protein area comprised CSFV amino acid residues 869-878 was constructed: W871T, W875D, and V878T. Interestingly, mutated virus FPi.c was completely attenuated when inoculated intranasally at a dose of 10.sup.5 TCID50 in swine. Importantly, animals infected with FPi.c virus were protected against the virulent challenge with Brescia virus at 3 and 28 days after vaccination. Protection was evidenced by absence of clinical signs related with CSF as well as the absence of viremia produced by the challenge virulent virus.

The present invention relates i.a. to a CSFV (classical swine fever virus) comprising a substitution of proline to lysine at amino acid position 44 of the E2 protein and a substitution of threonine to aspartic acid at amino acid position 45 of the E2 protein. Further, the present invention provides an immunogenic composition comprising the CSFV of the present invention and the use of the immunogenic composition for reducing the incidence of or severity in an animal of one or more clinical signs associated with CSF. Moreover, the present invention provides a method of differentiating animals infected with CSFV from animals vaccinated with the immunogenic composition of the present invention.

The present invention relates to chimeric pestiviruses having utility as immunogenic compositions and vaccines. Also described herein are methods and kits for treating or preventing the spread of bovine viral diarrhea virus infection, as well as methods and kits for differentiating between vaccinated and wild-type infected animals.