Survival and immunization of raccoons after exposure to pseudorabies (Aujeszky's disease) virus gene-deleted vaccines

In a controlled experiment, 16 wild-trapped raccoons were exposed to 1 of 2 genetically modified live pseudorabies virus (PRV) vaccines used in swine. One vaccine had genes deleted for thymidine kinase (TK^-) and glycoprotein G (gG^-); the other had an additional deletion for glycoprotein E (gE^-). These vaccines were administered orally and intranasally at four dose levels: 10³, 10⁴, 10⁵, and 10⁶ TCID₅₀. The 21 days survival rate was 37.5% for the gG^-TK^- vaccine; all of the survivors developed antibodies to PRV. All animals receiving the gG^-gE^-TK^- vaccine survived; 75% (all except the lowest dose) developed anti-PRV antibodies. Survivors were challenged intranasally with a 3.2×10³ TCID₅₀ dose of the virulent wildtype PRV Shope strain. Two of the remaining three gG^-TK^- vaccinated raccoons survived the challenge; for the gG^-gE^-TK^- vaccine, the survival rate was 50% (4/8). The raccoons with higher vaccine-induced antibody titers were more likely to survive the challenge with the virulent PRV; there was a 100% mortality rate for raccoons lacking detectable anti-PRV antibodies. This experiment indicates that exposure of raccoons to modified live gene-deleted PRV vaccines may result in an immune response, and that this immunity provides some protection against exposure to virulent virus.