Better immune efficacy triggered by the inactivated gI/gE-deleted pseudorabies virus with the additional insertion of gC gene in mice and weaned pigs

A new variant of pseudorabies virus (PRV) with high pathogenicity has been prevalent in many swineherds vaccinated with Bartha-K61 in China since 2011. Several gene-deleted vaccine candidates have been developed based on new emerging PRV variants. PRV-AH, a new emerging PRV strain from Anhui Province, was isolated in our laboratory in 2013. In the present study, rPRV-AH-gI⁻/gE⁻ and rPRV-AH-gI⁻/gE⁻/gC⁺ were generated based on PRV-AH by homologous recombination. The growth kinetics of rPRV-AH-gI⁻/gE⁻ and rPRV-AH-gI⁻/gE⁻/gC⁺ were similar to their parental strains. Compared with the commercial inactivated vaccine of Ea strain, the immune efficacy of the inactivated vaccine based on recombinant viruses was evaluated in mice and weaned pigs. The result showed that the level of neutralizing antibody in mice immunized with rPRV-AH-gI⁻/gE⁻/gC⁺ was higher compared with those immunized with rPRV-AH-gI⁻/gE- at a dose of 10⁶ TCID₅₀ at 8 weeks post initial immunization (p < 0.0001). Among the groups immunized at a dose of 10⁵ TCID₅₀, the rPRV-AH-gI⁻/gE⁻ group showed a survival rate of 37.5 %, while the rPRV-AH-gI⁻/gE⁻/gC⁺ group showed a protection rate of 87.5 % against the PRV-AH challenge. Besides, the rPRV-AH-gI⁻/gE⁻ and rPRV-AH-gI⁻/gE⁻/gC⁺ group immunized at a dose of 10⁶ TCID₅₀ showed a survival rate of 100 %. Interestingly, compared with the commercial vaccine group, the group of 10⁵ TCID₅₀ rPRV-AH-gI⁻/gE⁻/gC⁺ showed a lower level of neutralizing antibodies (p < 0.0001) but the same protection rate in mice. Moreover, in the pig experiment, the level of neutralizing antibodies in the group vaccinated with inactivated rPRV-AH-gI⁻/gE⁻/gC⁺ was higher than any other groups at 8 weeks post initial immunization (p < 0.05). More importantly, the milder symptoms and pathological lesions occurred in pigs vaccinated with rPRV-AH-gI⁻/gE⁻/gC⁺ after challenge with 10⁶ TCID₅₀ PRV-AH, revealing that additional insertion of gC gene could enhance the protective efficacy in PRV gI/gE-deleted vaccine in pigs. Collectively, these above-mentioned findings suggested that the inactivated vaccine of rPRV-AH-gI⁻/gE⁻/gC⁺ had a better immune efficacy, which could be regarded as a promising inactivated vaccine candidate for PRV control.