Vaccination of pigs against pseudorabies with highly attenuated vaccinia (NYVAC) recombinant viruses

Poxvirus recombinants, based on the highly attenuated NYVAC strain of vaccinia virus (Tartaglia et al., 1992), containing single gene inserts encoding the pseudorabies virus (PRV) gII, gIII, or gp50 glycoproteins were tested for their immunogenicity in pigs. Twenty-four pigs were randomly divided into six groups of four. Groups 1–3 were inoculated with 10 7 CCID 50 of NYVAC/PRV gII, NYVAC/PRV gIII, or NYVAC/PRV gp50, respectively, while groups 4 and 4 received the NYVAC parent virus or an inactivated PRV vaccine control, respectively. Group 6 represented the sham vaccinated control group. All inoculations were given by the intramuscular route on weeks 0 and 4. The candidate vaccines were shown to be safe with no local or systemic reactions. At 4 weeks following the second inoculation, all pigs were challenged by an oronasal administration of a virulent PRV strain. Pigs were monitored before and after challenge for clinical manifestations resulting from vaccination and challenge exposure, respectively. Sera were analyzed for PRV neutralizing activity. Virological analyses after challenge included assessment of virus shedding and the development of latent PRV infections. All but one animal developed latent PRV infection following challenge exposure; however, significant protection against PRV-induced signs was afforded by vaccination with either the NYVAC/PRV gp50 or NYVAC/PRV gII recombinant viruses, as well as with the inactivated PRV vaccine. The NYVAC/PRV gp50 also reduced overall virus shedding after challenge. The extent of protection against PRV-induced clinical signs, in general, was associated with the level of pre-challenge virus neutralizing activity.