DNA immunization of pigs using antigenic domains of the F2 glycoprotein of the classical swine fever virus

The classical swine fever virus (CSFV), etiologic agent of classical swine fever (hog cholera) infects pigs and wild boar of all ages. After an animal_s exposure to the virus, the incubation period spans about two to 14 days before disease becomes evident. The acute form of CSF, whose mortality rate approaches 100% in juvenile swine, is characterized by fever, anorexia, lethargy, multifocal hyperemia, hemorrhagic skin lesions, cyanosis of the skin and extremities, transient constipation followed by diarrhea, and occasional vomiting, dysporea, ataxia paresis, and convulsions. Government bureaus direct regular vaccination of swine with killed CSF viral particles, recombinant viruses or subunit vaccines. Unfortunately, these vaccines entail prohibitive production costs and risk reversion of attenuated strains to pathogenic forms. An alternative that addresses issues of vaccine cost, efficacy, and safety is DNA immunization. DNA vaccines are plasmids that contain only specific genes coding for immunogenic proteins. A DNA vaccine against classical swine fever was developed and tested for its immunogenicity and potency in pigs. A gene insert coding for the antigenic domains B/C and A of the glycoprotein E2 of the CSFV (Strain Brescia) was generated via overlap extension-PCR then cloned into a mammalian expression vector. Upon confirmation of successful DNA vaccine synthesis, endotoxin-free batches of the vaccine were prepared and administered to pigs. At set time points, sera were extracted from the test animals for analysis of the anti-CSFV antibody levels via competition ELISA. Upon completion of the immunization trial, representative pigs were challenged with a virulent strain of hog cholera virus. Although the DNA vaccine appeared less immunogenic than a modified live CSFV vaccine, pigs that received two doses of the DNA vaccine exhibited decreased susceptibility to infection than unvaccinated controls and animals previously treated with the modified live virus vaccine. The administration of a DNA vaccine coding for antigenic domains of the hog cholera E2 glycoprotein was able to elicit anti-E2 antibody production but appeared less immunogenic than a commercially available control vaccine. However, the DNA vaccine was also found to confer increased protection and was also able to increase the survival times of tests animals that have been challenged with a virulent strain of the hog cholera.