A deletion at the UL/IR junction reduces pseudorabies virus neurovirulence.

A recombinant pseudorabies virus (PRV), designated LLT beta delta 2, which contains a 3-kbp deletion spanning the junction of the unique long and internal repeat sequences was constructed. Compared with the parental strain and a virus rescued for the deleted sequences, LLT beta delta 2 exhibited similar replication characteristics in tissue culture. When inoculated intranasally in swine, LLT beta delta 2 was significantly reduced in virulence and did not produce neurological signs characteristic of PRV infection. LLT beta delta 2 replicated efficiently at the site of inoculation and in peripheral nervous tissues, but replication was restricted in the central nervous system. These results indicate the presence of a PRV neurovirulence determinant in the vicinity of the junction.