Recombinant classical swine fever (CSF) viruses derived from the Chinese vaccine strain (C-strain) of CSF virus retain their avirulent and immunogenic characteristics

Two recombinant classical swine fever (CSF) viruses (Flc2, Flc3) transcribe d from a DNA copy of the genome of the Chinese (C) strain, a CSF virus vacc ine strain, were characterized in vivo in rabbits and pigs. Rabbits were in oculated intravenously with Flc2 or Flc3, the parent C-strain virus, a biol ogically cloned C-strain or CSF virus strain Brescia (C.1.1.1). After 24-96 h fever was detected in the rabbits inoculated with the different C-strain viruses. Apart from those in the control group, all the C-strain inoculate d rabbits had developed CSF virus neutralizing antibodies 4 weeks later and were protected against a parent C-strain challenge. In the second experime nt, pigs were inoculated with the parent C-strain or recombinant C-strain v irus (Flc2 or Flc3) and then challenged after 4 weeks with the virulent CSF virus strain Brescia. None of the pigs showed clinical signs of classical swine fever after vaccination or challenge, whereas the control pigs develo ped clinical signs typical for acute CSF. Pigs inoculated with the differen t C-strain viruses were not viremic after inoculation or challenge, and CSF virus neutralizing antibodies were detected from day 14 onwards. The resul ts from both experiments demonstrated that the two recombinant viruses had retained the biological and immunogenic properties of the parent C-strain i n rabbits and pigs. We conclude that the full-length cDNA of the C-strain c an serve as a matrix for further development of a live recombinant CSF viru s marker vaccine. (C) 2000 Elsevier Science Ltd. All rights reserved.