Evaluation of the vaccinations with three strains of gene-deleted mutants from pseudorabies virus, PRV TK-, PRV gE-/gI and PRV TK-/gE-/gI- after exposure to the wild Fa strain / 中国人兽共患病学报

ABSTRACT

To evaluate the value of the vaccinations with 3 strains of gene-deleted mutants from pseudorabies virus(PRV), PRV TK-, PRV gE-/gI- and PRV TK-/gE-/gI- after to exposure to the wild Fa strain, these mutant strains from the PVR reference isolate Fa were used to vaccinate 4 weeks old PRV-free pigs with a dosage of 105 PFU each ,and followed by nasally challenged by the parental Fa strain with a dosage of 107 PFU at 14 days post vaccination. The pathological changes, virus discharge and distribution were evaluated after vaccination and challenge. It was found that the histopathological observations in the 10 collected samples including cerebrum, cerebellum, heart, liver, lungs, spleen, kidneys, tonsils, lymph nodes and trigeminal ganglion from these 3 mutant strains showed that the rates of occurrence of pathological changes in various organs were 4/10, 3/10 and 4/10 respectively, whereas that of the positive controls were 9/10. The damage in lungs was more serious in pigs vaccinated with PRV TK-mutant and positive control in comparison with other groups of pigs inoculated, and the damages in cerebrum, cerebellum and trigeminal ganglion in positive controls were more serious than those of pigs vaccinated with the 3 gene-deleted mutants. However, the tonsils, the main organ for latent infection were damaged mildly in the pigs inoculated with these 3 gene-deleted mutants in comparison with that of the positive controls. As demonstrated by Southern blot analysis, all the vaccinated pigs could discharge viruses by secretion through nasal cavity, but the soldier pigs were not infected successively by the gene-deleted mutants and the gene-deleted mutants were also unable to establish infection in cerebrum and cerebellum. Nevertheless, they could not effectively block discharge of PRV Fa after exposure to Fa virus, but could block effectively the virulent Fa virus invading into cerebrum and cerebellum. From these observation, it is evident that the deleted mutants of the TK, gE/gI , TK/gE/gI genes can block the invasion of virulent Fa virus into cerebrum and cerebellum and lessen the damages on multiple organs or tissues ,indicating that the deleted mutant of TK/gE/gI gene may be the most promising candidate of vaccine strain for development of the commercial vaccine.